Heater plate assembly in humidifier systems for medical use

Abstract

To provide an improved system and method for determining a low water and / or water depleted condition of a humidifier chamber of a respiratory or surgical humidifier system.SOLUTION: An improved system uses a specific frequency band to detect changes in a temperature of a heater plate 212. The temperature changes may correlate to a specific heat capacity value of the humidifier chamber 205. The low water and / or water depletion detection process can be performed without need to determine the gas flow rate and / or may be run continuously. A heater plate assembly of the system may include a compliant insulation sheet to improve thermal coupling between the heating element and the top heating plate of the heater plate assembly, thereby improving the low water and / or water depletion detection process.SELECTED DRAWING: Figure 2A

Description

[Technical Field]

[0001] Field of the Disclosure The present disclosure relates to respiratory and / or surgical humidifier systems, and respiratory or breathing assistance systems for gas delivery to a patient or user. [Background technology]

[0002] Respiratory devices are used in a variety of settings, such as hospitals, medical facilities, home care, palliative care, or home environments. In a variety of respiratory applications, it is beneficial to humidify the gas delivered to a patient or user. These applications include when the gas is intended for breathing by the patient or user and / or when the gas is delivered to the patient or user during surgery.

[0003] When breathing gas in a noninvasive mode, humidity increases patient or user comfort and improves the patient's or user's tolerance to noninvasive ventilation (NIV), as the inhaled gas passes through the upper airway, for example, when the gas is delivered to the patient or user via a face mask or nasal mask. The humidified gas reduces drying of the patient's or user's airway tissues (e.g., the nasal mucosa). For surgical gases or invasive modes when the gas delivered to the patient bypasses the upper airway, humidification of the gas has been shown to improve patient comfort and provide physiological benefits, such as improved mucus transport, and may be necessary for patient or user safety, for example, to prevent airway obstruction due to thickened respiratory secretions, disruption of the airway epithelium, and / or improve postoperative outcomes. For high-flow therapy, humidified gas is delivered to the patient or user at a high flow rate through a non-sealing interface. The patient or user may be spontaneously breathing or apneic, such as under anesthesia. A flow therapy device with a humidifier can be used to deliver high flow gases, and the therapy device may control characteristics of the gas flow, including, for example, flow rate, temperature, pressure, humidity, supplemental gas concentration, etc. In the case of positive airway pressure (PAP) therapy, a PAP therapy device including a blower and a humidifier can be used to provide pressure therapy to a user, for example, continuous positive airway pressure therapy (CPAP). Summary of the Invention [Problem to be solved by the invention]

[0004] In respiratory or surgical humidifier systems incorporating a humidifier chamber for humidifying gas for delivery to a patient or user, it is important to maintain a certain minimum water level so that the humidifier system can provide water vapor to the gas stream to humidify the gas. Therefore, it is important for the medical personnel administering the humidified gas to the patient or user, or the patient or user themselves in the case of home administration, to check the water level and, if necessary, add more water to the humidifier chamber. This step is sometimes overlooked, which can pose a risk to the patient or user due to prolonged exposure of the airway to dry gas, cause discomfort to the patient or user, and / or cause interruptions to the gas humidification operation, or in some cases, damage to the respiratory humidifier system. A lack of water and a dry chamber, such as one that runs out of water, can also reduce the amount of humidification delivered, thereby compromising therapy.

[0005] Some respiratory humidifier systems are capable of detecting a water-out condition and / or outputting a water-out alarm based on a determination of the thermal conductivity of the humidifier chamber. These systems may require input from flow and / or temperature sensors at various locations on the device, such as the heater plate of the humidifier chamber, the humidifier chamber outlet, and / or the patient or user end of the breathing circuit. As a result, respiratory humidifier systems that do not incorporate all of these flow and / or temperature sensors cannot implement such water-out detection and / or alarm functionality. [Means for solving the problem]

[0006] This disclosure provides examples of respiratory or surgical humidifier systems that can detect a water-out condition and / or output a humidifier chamber water-out alarm with input from a minimal number of sensors, e.g., as little as one temperature sensor at or near the heater plate. Accordingly, these water-out detection and / or alarm methods can be implemented in many types of humidification systems or other respiratory assistance devices that may include humidifiers, e.g., high-flow systems and / or CPAP systems. The water-out detection and / or alarm methods disclosed herein may be based on determining the specific heat capacity of the humidifier chamber (including its contents, such as water) by applying a supplementary power input waveform (also referred to herein as a supplementary signal or characteristic energization signal) and determining the magnitude and / or phase of a heater plate temperature signal and / or temperature reading from a temperature signal at or near the heater plate that has been filtered at a predetermined frequency. The application of the complementary signal may be performed by applying the complementary signal as the heater plate's signal (e.g., during standby mode) or by injecting the complementary signal into the heater plate control signal (e.g., by summing, modulating, interleaving, cycling the heater plate control signal and the complementary signal, or using any other scheme for transmitting two signals on the same transmission line). This complementary waveform may be superimposed on a normal heater plate control signal, such as a normally operating heater plate power signal, without biasing the normal control. The complementary waveform may be periodic or cyclic and / or have zero mean. The waveform may ensure that the normal control is not biased. The frequency of the complementary signal may be a predetermined frequency. The frequency may be selected to be isolated in the frequency domain from the normal control response. The selected frequency may help avoid interference with the normal control of the heater plate.In one example, the frequency of the complementary signal can be higher than (e.g., at least 1.5 times higher than or other value disclosed herein) a conventional heater plate control signal (such as in normal operation for heating a humidification chamber disposed on the heater plate) and can output a duty cycle, etc., for heating the heater plate.

[0007] Throughout this disclosure, the specific heat capacity of a humidifier chamber refers to the specific heat capacity of the humidifier chamber including its contents, such as water, unless expressly stated otherwise.

[0008] In addition to requiring fewer sensors, the water out detection and / or alarm methods disclosed herein may also have any of the following and / or other advantages. For example, the water out detection and / or alarm systems disclosed herein are based on the principle of specific heat capacity, which is inherently related to water volume. This allows the system to be independent of gas flow rate. Flow rate independence can allow the water out detection and / or alarm method to be more suitable for low-flow noninvasive therapies (e.g., pediatric noninvasive therapy flow rates of less than about 10 L / min) or very low-flow invasive therapies (e.g., neonatal invasive therapy flow rates of less than about 5 L / min) compared to flow rate-dependent detection methods. Flow rate independence can also allow the water out detection and / or alarm method to be insensitive to flow sensor errors or avoid the need to make assumptions about the flow state of the system. Because the water out / alarm methods described herein can function on a variety of different platforms and / or types of chambers, using specific heat capacity as a parameter to determine water out is also advantageous. The described water out approach is more flexible and versatile. Furthermore, the disclosed method of detecting water shortage can determine a water shortage condition (water-free or substantially water-free) when there is no gas flow through the humidifier, such as when it is on standby.

[0009] The water outage detection and / or alarm methods disclosed herein can also be independent of or invariant to humidity delivery. As a result, the methods disclosed herein may be more suitable for gas delivery situations that result in lower humidity, such as non-invasive therapies using room air entrainment and / or turbine-driven flow sources. In these cases, the inlet humidity may be high (e.g., greater than about 10 mg / L), the inlet gas temperature may be high (e.g., greater than about 30 degrees Celsius), and / or ambient temperature conditions may be high (e.g., greater than about 25 degrees Celsius). This may lead to reduced humidity addition requirements, which may adversely affect conventional water outage detection methods. Similar water outage methods disclosed herein may also be used in high flow modes or any other operating modes.

[0010] The present disclosure also provides an improved heater plate structure that can improve the heater plate's thermal coupling and reduce heat transfer inefficiencies through modeled heater plate R and C components. In particular, an improved heater plate assembly including a resilient electrical insulator can reduce the complementary signal for water outage detection and return a feedback signal with increased amplitude. The feedback signal has an improved signal-to-noise ratio. The resilient electrical insulator can be flexible and / or compliant, as described below. A compliant material can refer to the ability of a material to soften, be compressible, and / or conform to the shape of a surface. For example, a compliant material may be able to displace an air gap between the surfaces of other materials that can sandwich the compliant material. Throughout this disclosure, an insulating material can refer to an electrically insulating material that can also be thermally conductive.

[0011] The controller of the respiratory humidifier system disclosed herein can apply a complementary signal to the heater plate control signal rather than simply varying the heater plate's power input and waiting for a specific response from the heater plate and / or humidifier chamber during a water-out event. In some exemplary configurations, the controller may apply the complementary signal continuously. The controller may apply the complementary signal to the heater plate continuously and / or intermittently. The controller may measure the response to the complementary signal. The controller may continuously and / or intermittently sample the response to the complementary signal. Thus, the detection and / or alarm process need not rely on complex state transitions (such as transitions between low-flow and high-flow states) and / or trigger conditions. The processes described herein can be performed continuously without affecting normal operation of energizing the heater plate, and thus can provide adjustable detection times and thresholds so that a warning can be given before the humidifier chamber actually runs out of water. The water-out detection method described herein is also advantageous because the method does not require an interruption of therapy, including an interruption of control of the heater plate to heat or cool the heater. The complementary signal can be at a frequency substantially different from the normal operating frequency (i.e., the heater plate control operating frequency) and is of zero mean so that no net energy is introduced into the system. The water out detection methods described herein can have minimal negative impact on humidity generation or delivery of humidified gas to the patient or user.

[0012] As described in more detail below, the detection and / or alarm method may also be highly noise tolerant because the signal of interest is naturally filtered to the frequency of the complementary signal, also referred to herein as the applied frequency.

[0013] The detection and / or alarm methods described herein can be incorporated into a variety of respiratory and / or surgical humidifier systems, such as CPAP devices, high flow therapy devices, surgical humidifiers, respiratory humidifiers, infant CPAP, infant high flow, NIV therapy, etc.

[0014] In some configurations, a multi-layer heater plate assembly for a respiratory humidifier can include an upper heating plate, a heating element configured to generate heat, and a double insulating mechanism configured to provide electrical insulation between the heating plate and the heating element, the double insulating mechanism including two insulating elements, a first insulating element of the two insulating elements having a first flexibility and a second insulating element of the two insulating elements having a second flexibility different from the first flexibility.

[0015] In some configurations, the multi-layer heater plate assemblies may be removably coupled to one another by one or more fasteners.

[0016] In some configurations, a multi-layer heater plate assembly can be formed by bolting a lower plate to an upper heating plate, with a heating element and double insulation mechanism between the lower plate and the upper heating plate.

[0017] In some configurations, the upper heating plate may include a sensor mounting block configured to receive at least one temperature sensor.

[0018] In some configurations, the sensor mounting block may be configured to receive two temperature sensors.

[0019] In some configurations, the at least one temperature sensor may include a thermistor.

[0020] In some configurations, the safety feature may include a thermal cutoff unit.

[0021] In some configurations, the lower plate may include a platform for supporting the safety feature.

[0022] In some configurations, the safety feature may be secured to the platform by a screw.

[0023] In some configurations, the platform may protrude from the remainder of the lower plate.

[0024] In some configurations, the bottom plate may include slots where the safety features are bonded to the bottom plate to improve isolation of the safety features from the heating element.

[0025] In some configurations, the bottom plate may further include a cut-out step along the length of the slot.

[0026] In some configurations, the slot may be L-shaped.

[0027] In some configurations, the slots may terminate at or near the periphery of the heating element.

[0028] In some configurations, the slots may extend radially outward beyond the periphery of the double insulation feature.

[0029] In some configurations, the bottom plate may include a cutout step near the sensor mounting block when the heater plate assembly is assembled.

[0030] In some configurations, one insulating element of the double insulating mechanism may be more flexible or compliant than the other insulating element, and in some configurations, the first insulating element may be more flexible than the second insulating element.

[0031] In some configurations, one insulating element of the dual electrical isolation mechanism may include a compliant insulating material configured to displace an air gap between the upper heating plate and the heating element.

[0032] In some configurations, one insulating element of the double electrical insulation mechanism may include a flexible insulating material.

[0033] In some configurations, a first insulating element can have a first flexibility and a second insulating element can have a second flexibility, such that one of the insulating elements is softer than the other.

[0034] In some configurations, the first insulating element may include a resilient material.

[0035] In some configurations, one of the insulating elements may have a Shore 00 hardness scale of 50-100.

[0036] In some configurations, one of the insulating elements may have a Shore 00 hardness scale of 80.

[0037] In some configurations, the two insulating elements may include at least one non-flexible insulating layer.

[0038] In some configurations, the at least one non-flexible insulating layer may include mica.

[0039] In some configurations, the assembly may include a layer of compliant insulating material.

[0040] In some configurations, the multi-layer heater plate assembly may further include an additional layer of compliant insulating material configured to displace air gaps between components of the heater plate assembly.

[0041] In some configurations, the two insulating elements may include two non-flexible insulating layers.

[0042] In some configurations, the assembly may include two layers of compliant insulating material.

[0043] In some configurations, the two insulating elements may include two layers of compliant insulating material configured to displace an air gap between components of the heater plate assembly.

[0044] In some configurations, the compliant insulating material may include a thermally conductive but electrically insulating elastomer.

[0045] In some configurations, the compliant insulating material may include silicone or a silicone compound.

[0046] In some configurations, the compliant insulating material may include a fiberglass substrate and a thermally conductive material embedded in or disposed on the substrate.

[0047] In some configurations, the compliant insulating material may have a breakdown voltage of at least 4000V AC.

[0048] In some configurations, the compliant insulating material may have a breakdown voltage of at least 6000V AC.

[0049] In some configurations, the compliant insulating material may have a thermal conductivity of at least 1.8 W / (mK).

[0050] In some configurations, a multi-layer heater plate assembly for a respiratory humidifier can include an upper heating plate, a lower plate, a heating element configured to generate heat, the heating element being defined by the upper and lower plates, a first resilient insulating material between the upper heating plate and the heating element, and a second resilient insulating material between the lower plate and the heating element, wherein the first resilient insulating material and the second resilient insulating material can occupy an air gap between the upper heating plate and the heating element and an air gap between the lower plate and the heating element, respectively. The first insulating material or the second insulating material is an electrically insulating material. In some configurations, the first resilient electrically insulating material and the second resilient electrically insulating material can displace the air gap between the upper heating plate and the heating element and the air gap between the lower plate and the heating element, respectively.

[0051] In some configurations, the multi-layer heater plate assemblies may be removably coupled to one another by one or more fasteners.

[0052] In some configurations, a multi-layer heater plate assembly can be formed by bolting a lower plate to an upper heating plate, with the heating element and first and second resilient insulating materials between the lower plate and the upper heating plate.

[0053] In some configurations, the first resilient insulating material and / or the second resilient insulating material may have a hardness of 50-100 on the Shore 00 hardness scale.

[0054] In some configurations, the first resilient insulating material and / or the second resilient insulating material may have a hardness of 80 on the Shore 00 scale.

[0055] In some configurations, the assembly may include a double electrical insulation mechanism that includes two insulating elements.

[0056] In some configurations, the two insulating elements may include two non-flexible electrically insulating layers.

[0057] In some configurations, the multi-layer heater plate assembly may further include a non-flexible electrically insulating layer.

[0058] In some configurations, the non-flexible electrically insulating layer may include mica.

[0059] In some configurations, the two insulating elements may include two layers separate from each other.

[0060] In some configurations, the first resilient electrically insulating material and the second resilient electrically insulating material may comprise two separate layers.

[0061] In some configurations, the first resilient, electrically insulating material and / or the second resilient, electrically insulating material may comprise a thermally conductive, yet electrically insulating, elastomer.

[0062] In some configurations, the first resilient electrically insulating material and / or the second resilient electrically insulating material may include silicone or a silicone compound.

[0063] In some configurations, the first resilient electrically insulating material and / or the second resilient electrically insulating material may include a fiberglass substrate and a thermally conductive material embedded in or disposed on the substrate.

[0064] In some configurations, the first resilient, electrically insulating material and / or the second resilient, electrically insulating material may have a breakdown voltage of at least 4000V AC.

[0065] In some configurations, the first resilient, electrically insulating material and / or the second resilient, electrically insulating material may have a breakdown voltage of at least 6000V AC.

[0066] In some configurations, the first resilient, electrically insulating material and / or the second resilient, electrically insulating material may have a thermal conductivity of at least 1.8 W / (mK).

[0067] In some configurations, the first resilient electrically insulating material and / or the second resilient electrically insulating material may comprise a compliant material configured to displace air gaps between components of the multi-layer heater plate assembly.

[0068] In some configurations, the upper heating plate may comprise a metal.

[0069] In some configurations, the upper heating plate may include a cavity on the lower surface and an exposed upper surface for contacting the base of the humidifier chamber of the respiratory humidifier.

[0070] In some configurations, the upper heating plate may include a sensor mounting block configured to receive at least one temperature sensor.

[0071] In some configurations, the sensor mounting block may be configured to receive two temperature sensors.

[0072] In some configurations, the at least one temperature sensor may include a thermistor.

[0073] In some configurations, the safety feature may include a thermal cutoff unit.

[0074] In some configurations, the lower plate may include a platform for supporting the safety feature.

[0075] In some configurations, the safety feature may be secured to the platform by a screw.

[0076] In some configurations, the platform may protrude from the remainder of the lower plate.

[0077] In some configurations, the bottom plate may include slots where the safety features are bonded to the bottom plate to improve isolation of the safety features from the heating element.

[0078] In some configurations, the bottom plate may further include a cutout step along the length of the slot.

[0079] In some configurations, the slot may be L-shaped.

[0080] In some configurations, the slots may terminate at or near the periphery of the heating element.

[0081] In some configurations, the slots may extend radially outward beyond the periphery of the double insulation feature.

[0082] In some configurations, the bottom plate may include a cutout step near the sensor mounting block when the heater plate assembly is assembled.

[0083] In some configurations, a multi-layer heater plate assembly for a respiratory humidifier may include an upper heating plate, a heating element configured to generate heat, the heating element located below the upper heating plate, and a thermal interface layer between the upper heating plate and the heating element, the thermal interface layer including a compliant thermal interface material configured to displace an air gap between the upper heating plate and the heating element.

[0084] In some configurations, the thermal interface layer may be configured to displace an air gap between the upper heating plate and the heating element to improve thermal conductivity between the upper heating plate and the heating element.

[0085] In some configurations, the multi-layer heater plate assemblies may be removably coupled to one another by one or more fasteners.

[0086] In some configurations, the multi-layer heater plate assembly can include a lower plate, with the heating element being defined by the upper heating plate and the lower plate.

[0087] In some configurations, the thermal interface layer may include a thickness sufficient to provide electrical insulation.

[0088] In some configurations, a multi-layer heater plate assembly can be formed by bolting a lower plate to an upper heating plate, with the heating element and thermal interface layer between the lower plate and the upper heating plate.

[0089] In some configurations, the upper heating plate may include a sensor mounting block configured to receive at least one temperature sensor.

[0090] In some configurations, the sensor mounting block may be configured to receive two temperature sensors.

[0091] In some configurations, the at least one temperature sensor may include a thermistor.

[0092] In some configurations, the multi-layer heater plate assembly may further include a safety feature coupled to the bottom plate.

[0093] In some configurations, the safety feature may include a thermal cutoff unit.

[0094] In some configurations, the lower plate may include a platform for supporting the safety feature.

[0095] In some configurations, the safety feature may be secured to the platform by a screw.

[0096] In some configurations, the platform may protrude from the remainder of the lower plate.

[0097] In some configurations, the bottom plate may include slots where the safety features are bonded to the bottom plate to improve isolation of the safety features from the heating element.

[0098] In some configurations, the bottom plate may further include a cutout step along the length of the slot.

[0099] In some configurations, the slot may be L-shaped.

[0100] In some configurations, the slots may terminate at or near the periphery of the heating element.

[0101] In some configurations, the slots may extend radially outward beyond the periphery of the thermal interface layer.

[0102] In some configurations, the bottom plate may include a cutout step near the sensor mounting block when the heater plate assembly is assembled.

[0103] In some configurations, the thermal interface layer may have a hardness scale of 50-100 Shore 00.

[0104] In some configurations, the thermal interface layer may have a hardness of 70-90 on the Shore 00 scale.

[0105] In some configurations, the thermal interface layer may have a hardness of 80 on the Shore 00 scale.

[0106] In some configurations, the thermal interface material may be electrically insulating.

[0107] In some configurations, the multi-layer heater plate assembly may further include a second layer of compliant insulating material configured to displace air gaps between components of the multi-layer heater plate assembly.

[0108] In some configurations, a second thermal interface layer may be located between the heating element and the bottom plate.

[0109] In some configurations, the second thermal interface layer may be located between the upper heating plate and the lower plate.

[0110] In some configurations, the multi-layer heater plate assembly may include at least one non-flexible, electrically insulating layer.

[0111] In some configurations, at least one non-flexible, electrically insulating layer may be located between the compliant thermal interface layer and the heating element.

[0112] In some configurations, the multi-layer heater plate assembly may include at least one non-flexible, electrically insulating layer between the heating element and the bottom plate.

[0113] In some configurations, the multi-layer heater plate assembly may include two non-flexible, electrically insulating layers between the heating element and the bottom plate.

[0114] In some configurations, the at least one non-flexible electrically insulating layer may include mica.

[0115] In some configurations, the second thermal interface layer may be electrically conductive.

[0116] In some configurations, the compliant thermal interface material may include a thermally conductive but electrically insulating elastomer.

[0117] In some configurations, the compliant thermal interface material may include silicone or a silicone compound.

[0118] In some configurations, the compliant thermal interface material may include a fiberglass substrate and a thermally conductive material embedded in or disposed on the substrate.

[0119] In some configurations, the compliant thermal interface material may have a breakdown voltage of at least 4000V AC.

[0120] In some configurations, the compliant thermal interface material may have a breakdown voltage of at least 6000V AC.

[0121] In some configurations, the compliant thermal interface material may have a thermal conductivity of at least 1.8 W / (mK).

[0122] In some configurations, the compliant thermal interface material may be elastic.

[0123] In some configurations, a multi-layer heater plate assembly for a respiratory humidifier may include an upper heating plate, a lower plate, a heating element configured to generate heat, the heating element defined by the upper and lower plates, and a compliant thermal interface layer between the lower and upper heating plates and configured to displace an air gap between the lower and upper heating plates.

[0124] In some configurations, the multi-layer heater plate assemblies may be removably coupled to one another by one or more fasteners.

[0125] In some configurations, a multi-layer heater plate assembly can be formed by bolting a lower plate to an upper heating plate, with a heating element and double electrical insulation between the lower plate and the upper heating plate.

[0126] In some configurations, the upper heating plate may include a sensor mounting block configured to receive at least one temperature sensor.

[0127] In some configurations, the sensor mounting block may be configured to receive two temperature sensors.

[0128] In some configurations, the at least one temperature sensor may include a thermistor.

[0129] In some configurations, the multi-layer heater plate assembly may further include a safety feature coupled to the bottom plate.

[0130] In some configurations, the safety feature may include a thermal cutoff unit.

[0131] In some configurations, the lower plate may include a platform for supporting the safety feature.

[0132] In some configurations, the safety feature may be secured to the platform by a screw.

[0133] In some configurations, the platform may protrude from the remainder of the lower plate.

[0134] In some configurations, the bottom plate may include slots where the safety features are bonded to the bottom plate to improve isolation of the safety features from the heating element.

[0135] In some configurations, the bottom plate may further include a cutout step along the length of the slot.

[0136] In some configurations, the slot may be L-shaped.

[0137] In some configurations, the slots may terminate at or near the periphery of the heating element.

[0138] In some configurations, the slots may extend radially outward beyond the periphery of the compliant thermal interface layer.

[0139] In some configurations, the bottom plate may include a cutout step near the sensor mounting block when the heater plate assembly is assembled.

[0140] In some configurations, the compliant thermal interface layer may be configured to displace the air gap between the edge of the lower plate and the upper heating plate.

[0141] In some configurations, the compliant thermal interface layer may have a hardness of 50-100 on the Shore 00 hardness scale.

[0142] In some configurations, the compliant thermal interface layer may have a hardness of 70-90 on the Shore 00 hardness scale.

[0143] In some configurations, the compliant thermal interface layer may have a hardness of 80 on the Shore 00 scale.

[0144] In some configurations, the compliant thermal interface layer may be electrically insulating.

[0145] In some configurations, the multi-layer heater plate assembly may include a second thermal interface layer configured to displace an air gap between the upper heating plate and the heating element.

[0146] In some configurations, the second thermal interface layer may be electrically conductive.

[0147] In some configurations, the multi-layer heater plate assembly may include at least one non-flexible, electrically insulating layer.

[0148] In some configurations, the at least one non-flexible electrically insulating layer may include mica.

[0149] In some configurations, at least one non-flexible, electrically insulating layer may be located between the compliant thermal interface layer and the heating element.

[0150] In some configurations, at least one non-flexible, electrically insulating layer may be located between the heating element and the lower plate.

[0151] In some configurations, the compliant thermal interface layer may include a thermally conductive but electrically insulating elastomer.

[0152] In some configurations, the compliant thermal interface layer may include a silicone or silicone compound.

[0153] In some configurations, the compliant thermal interface layer may include a fiberglass substrate and a thermally conductive material embedded in or disposed on the substrate.

[0154] In some configurations, the compliant thermal interface layer may have a breakdown voltage of at least 4000V AC.

[0155] In some configurations, the compliant thermal interface layer may have a breakdown voltage of at least 6000V AC.

[0156] In some configurations, the compliant thermal interface layer may have a thermal conductivity of at least 1.8 W / (mK).

[0157] In some configurations, the compliant thermal interface layer may be elastic.

[0158] In some configurations, a multi-layer heater plate assembly for a respiratory humidifier may include an upper heating plate, a heating element configured to generate heat, the heating element located below the upper heating plate, and a thermal interface layer between the upper heating plate and the heating element, the thermal interface layer comprising a resilient thermal interface material.

[0159] In some configurations, the multi-layer heater plate assemblies may be removably coupled to one another by one or more fasteners.

[0160] In some configurations, a multi-layer heater plate assembly can be formed by bolting a lower plate to an upper heating plate, with a heating element and first and second resilient, electrically insulating materials between the lower and upper heating plates.

[0161] In some configurations, the resilient, electrically insulating material may have a hardness scale of 50-100 Shore 00.

[0162] In some configurations, the resilient, electrically insulating material may have a hardness scale of 70-90 Shore 00.

[0163] In some configurations, the resilient, electrically insulating material may have a hardness of 80 on the Shore 00 scale.

[0164] In some configurations, the multi-layer heater plate assembly may include a non-flexible, electrically insulating layer.

[0165] In some configurations, the non-flexible electrically insulating layer may include mica.

[0166] In some configurations, the resilient, electrically insulating material may include a thermally conductive, yet electrically insulating, elastomer.

[0167] In some configurations, the resilient, electrically insulating material may include silicone or a silicone compound.

[0168] In some configurations, the resilient, electrically insulating material may include a fiberglass substrate and a thermally conductive material embedded in or disposed on the substrate.

[0169] In some configurations, the resilient, electrically insulating material may have a breakdown voltage of at least 4000V AC.

[0170] In some configurations, the resilient, electrically insulating material may have a breakdown voltage of at least 6000V AC.

[0171] In some configurations, the resilient, electrically insulating material may have a thermal conductivity of at least 1.8 W / (mK).

[0172] In some configurations, the upper heating plate may comprise a metal.

[0173] In some configurations, the upper heating plate may include a cavity on the lower surface and an exposed upper surface for contacting the base of the humidifier chamber of the respiratory humidifier.

[0174] In some configurations, the upper heating plate may include a sensor mounting block configured to receive at least one temperature sensor.

[0175] In some configurations, the sensor mounting block may be configured to receive two temperature sensors.

[0176] In some configurations, the at least one temperature sensor may include a thermistor.

[0177] In some configurations, the multi-layer heater plate assembly may further include a safety feature coupled to the bottom plate.

[0178] In some configurations, the safety feature may include a thermal cutoff unit.

[0179] In some configurations, the lower plate may include a platform for supporting the safety feature.

[0180] In some configurations, the safety feature may be secured to the platform by a screw.

[0181] In some configurations, the platform may protrude from the remainder of the lower plate.

[0182] In some configurations, the bottom plate may include slots where the safety features are bonded to the bottom plate to improve isolation of the safety features from the heating element.

[0183] In some configurations, the bottom plate may further include a cutout step along the length of the slot.

[0184] In some configurations, the slot may be L-shaped.

[0185] In some configurations, the slots may terminate at or near the periphery of the heating element.

[0186] In some configurations, the slots may extend radially outward beyond the periphery of the first resilient insulating material and / or the second resilient insulating material.

[0187] In some configurations, the bottom plate may include a cutout step near the sensor mounting block when the heater plate assembly is assembled.

[0188] In some configurations, a humidifier system for use in a medical procedure can include a base unit and a humidifier chamber receivable on the base unit, which can include any of the multi-layer heater plate assembly examples described above.

[0189] In some configurations, the humidifier chamber can include a conductive base that is forced into contact with the heater plate assembly when the humidifier chamber is placed on the base unit.

[0190] In some configurations, the heater plate assembly can heat the humidifier chamber to heat the contents of the chamber in order to humidify the gases passing through the chamber.

[0191] In some configurations, the system may include a tube configured to carry gas from the humidifier chamber to the patient interface.

[0192] In some configurations, a humidifier system for use in a medical procedure can include a housing configured to receive a humidifier chamber; a heater plate assembly located at least partially within the housing, the heater plate assembly including an upper heating plate configured to contact a base of the humidifier chamber when the humidifier chamber is received by the housing; a thermistor located on or near the upper heating plate; a heating element configured to generate heat; and an electrical isolation mechanism between the upper heating plate and the heating element, wherein the electrical isolation mechanism can thermally couple the heating element and the upper heating plate such that heat generated by a power signal to the heating element is transferred to the upper heating plate.

[0193] In some configurations, the electrical isolation feature can improve thermal coupling between the heating element and the upper heating plate.

[0194] In some configurations, a humidifier system for use in a medical procedure can include a housing configured to receive a humidifier chamber, a heater plate assembly located at least partially within the housing, the heater plate assembly including an upper heating plate configured to contact a base of the humidifier chamber when the humidifier chamber is received by the housing, a thermistor located on or near the upper heating plate, a heating element configured to generate heat, and an electrical isolation mechanism between the upper heating plate and the heating element, the electrical isolation mechanism can thermally couple the heating element and the upper heating plate such that heat generated by a power signal to the heating element is transferred to the upper heating plate. In some configurations, the electrical isolation mechanism can improve thermal coupling between the heating element and the upper heating plate.

[0195] In some configurations, the electrical isolation mechanism may include a flexible or compliant insulating sheet.

[0196] In some configurations, the electrical isolation mechanism may include a resilient insulating sheet.

[0197] In some configurations, the electrical isolation mechanism may include a compliant insulating sheet configured to displace an air gap between the upper heating plate and the heating element.

[0198] In some configurations, a flexible or compliant insulating sheet can improve heat conduction from the heating element to the upper heating plate.

[0199] In some configurations, the electrically insulating sheet can improve heat conduction from the heating element to the upper heating plate.

[0200] In some configurations, the flexible or compliant insulating sheet can reduce the capacitance of the heater plate assembly so as to improve thermal conductivity between components of the heater plate assembly.

[0201] In some configurations, the electrically insulating sheet can reduce the capacitance of the heater plate assembly so as to improve thermal conductivity between components of the heater plate assembly.

[0202] In some configurations, the system may include a double electrical isolation mechanism that includes two isolation elements.

[0203] In some configurations, the two insulating elements may include two non-flexible insulating layers.

[0204] In some configurations, the two non-flexible insulating layers may include mica.

[0205] In some configurations, the two insulating elements may include two layers separate from each other.

[0206] In some configurations, a double electrical isolation mechanism may be located between the electrical isolation mechanism and the heating element.

[0207] In some configurations, the electrical isolation mechanism may include a thermally conductive but electrically insulating elastomer.

[0208] In some configurations, the electrical isolation mechanism may include silicone or a silicone compound.

[0209] In some configurations, the electrical isolation feature may include a fiberglass substrate and a thermally conductive material embedded in or disposed on the substrate.

[0210] In some configurations, the electrical isolation feature includes a material having a breakdown voltage of at least 4000V AC.

[0211] In some configurations, the electrical isolation feature may include a material having a breakdown voltage of at least 6000V AC.

[0212] In some configurations, the electrical isolation feature may include a material having a thermal conductivity of at least 1.8 W / (mK).

[0213] In some configurations, the isolation feature can improve thermal coupling between the heating element and the upper heating plate such that the waveform applied to the power signal to detect a low or out of water condition in the humidifier chamber can be a reduced power waveform. In some configurations, the isolation feature can improve thermal coupling between the heating element and the upper heating plate such that the waveform injected into the power signal to detect a low or out of water condition in the humidifier chamber can be a reduced power waveform.

[0214] In some configurations, the electrical isolation feature can improve thermal coupling between the heating element and the upper heating plate so that the temperature reading of the thermistor better corresponds to the temperature of the water in the humidifier chamber.

[0215] In some configurations, the heater plate assembly can include a lower plate, and the heating element and electrical isolation mechanism can be defined between the lower plate and the upper heating plate.

[0216] In some configurations, the bottom plate may contact an electrical isolation mechanism.

[0217] In some configurations, the heater plate assembly may include a flexible or compliant insulating sheet between the upper heating plate and the lower plate.

[0218] In some configurations, the heater plate assembly may include a flexible, electrically insulating sheet between the upper heating plate and the lower plate.

[0219] In some configurations, the heater plate assembly may include a compliant electrically insulating sheet between the upper heating plate and the lower plate configured to displace an air gap between the upper heating plate and the lower plate.

[0220] In some configurations, the upper heating plate may include a sensor mounting block configured to receive at least one temperature sensor.

[0221] In some configurations, the sensor mounting block may be configured to receive two temperature sensors.

[0222] In some configurations, the temperature sensor may include a thermistor.

[0223] In some configurations, the safety feature may include a thermal cutoff unit.

[0224] In some configurations, the lower plate may include a platform for supporting the safety feature.

[0225] In some configurations, the safety feature may be secured to the platform by a screw.

[0226] In some configurations, the platform may protrude from the remainder of the lower plate.

[0227] In some configurations, the bottom plate may include slots where the safety features are bonded to the bottom plate to improve isolation of the safety features from the heating element.

[0228] In some configurations, the bottom plate may further include a cutout step along the length of the slot.

[0229] In some configurations, the slot may be L-shaped.

[0230] In some configurations, the slots may terminate at or near the periphery of the heating element.

[0231] In some configurations, the slots may extend radially outward beyond the periphery of the double insulation feature.

[0232] In some configurations, the bottom plate may include a cutout step near the sensor mounting block when the heater plate assembly is assembled.

[0233] In some configurations, a respiratory or surgical humidifier system with low water and / or out-of-water detection may include a base unit including a heater plate including one or more heating elements and a hardware controller in electronic communication with and configured to energize the one or more heating elements of the heater plate. In some configurations, the system may further include a humidifier chamber defining a volume and including a conductive base, the conductive base being receivable on the base unit such that the conductive base contacts the heater plate, the humidifier chamber being configured to maintain a water level. In some configurations, the hardware controller may be configured to determine a value from which a specific heat capacity of the humidifier chamber can be inferred and to determine a low water or out-of-water condition based at least in part on the determined value from which the specific heat capacity can be inferred.

[0234] In some configurations, the hardware controller may be configured to determine a specific heat capacity value of the humidifier chamber and determine a low or out of water condition based at least in part on the determined specific heat capacity value.

[0235] In some configurations, the hardware controller can determine that a low water or out-of-water condition exists in response to the determined specific heat capacity value being less than a threshold. In some configurations, the hardware controller can determine that a low water or out-of-water condition exists in response to the determined value from which the specific heat capacity can be inferred being less than a threshold.

[0236] In some configurations, the hardware controller can continuously determine the specific heat capacity value. In some configurations, the hardware controller can continuously determine a value from which the specific heat capacity can be inferred.

[0237] In some configurations, the hardware controller can continuously determine the specific heat capacity value. In some configurations, the hardware controller can continuously determine a value from which the specific heat capacity can be inferred.

[0238] In some configurations, the specific heat capacity value may be determined as a numerical score. In some configurations, the value from which the specific heat capacity can be inferred may be a numerical score.

[0239] In some configurations, the system may include a temperature sensor coupled to or adjacent to the heater plate, the temperature sensor determining the temperature of the heater plate.

[0240] In some configurations, the temperature sensor may include a thermistor.

[0241] In some configurations, the temperature sensor may include two thermistors, each acting as a voltage divider.

[0242] In some configurations, the hardware controller can determine the temperature value from the voltage readings of the two thermistors.

[0243] In some configurations, the hardware controller can determine a specific heat capacity value based on a temperature reading of the temperature sensor. In some configurations, the hardware controller can determine a value from which the specific heat capacity can be inferred based on a temperature reading of the temperature sensor.

[0244] In some configurations, the hardware controller is configured to apply a characteristic energization signal to one or more heating elements of the heater plate, process a temperature signal from a temperature sensor corresponding to the characteristic energization signal, determine a specific heat capacity value based on the temperature signal, and output a low water or low water warning in response to the determined specific heat capacity value being less than a threshold. In some configurations, the hardware controller is configured to determine a value from which the specific heat capacity can be inferred based on the temperature signal, and output a low water or low water warning in response to the determined value from which the specific heat capacity can be inferred being less than a threshold.

[0245] In some configurations, the hardware controller may be configured to apply the characteristic energization signal continuously. In some configurations, the hardware controller may be configured to apply the characteristic energization signal intermittently.

[0246] In some configurations, the hardware controller may be configured to apply the characteristic energization signal to the heater plate control signal. In some configurations, the characteristic energization signal may be applied by injection into the heater plate control signal. In some configurations, the hardware controller may be configured to apply the characteristic energization signal to a power control line that provides the heater plate control signal.

[0247] In some configurations, the characteristic energization signal may be higher in frequency than the heater plate control signal.

[0248] In some configurations, the hardware controller may pass the temperature measurement of the temperature sensor through a filter, such as a bandpass filter or a highpass filter, having a filter frequency corresponding to the frequency of the characteristic energization signal, so as to pass the temperature measurement corresponding to the frequency of the characteristic energization signal. In some configurations, the filter may be a direct conversion receiver, such as a homodyne, or an infinite impulse response filter.

[0249] In some configurations, temperature measurements corresponding to the frequency of the characteristic energization signal can be used to determine a specific heat capacity value. In some configurations, temperature measurements corresponding to the frequency of the characteristic energization signal can be used to determine a value from which the specific heat capacity can be inferred.

[0250] In some configurations, the heater plate may include any of the heater plate assembly examples described above.

[0251] In some configurations, the system may include one or more features of the humidifier systems described above for use in medical procedures.

[0252] In some configurations, a respiratory or surgical humidifier system with low water and / or out-of-water detection may include a base unit including a heater plate including one or more heating elements, a hardware controller in electronic communication with the one or more heating elements of the heater plate and configured to energize the one or more heating elements of the heater plate, and a temperature sensor coupled to or adjacent to the heater plate, the temperature sensor configured to generate a signal indicative of the temperature of the heater plate. In some configurations, the system may include a humidifier chamber defining a volume and including a conductive base, the conductive base receivable on the base unit such that the conductive base contacts the heater plate, the humidifier chamber configured to maintain a water level. In some configurations, the hardware controller may be configured to apply a characteristic energization signal to one or more heating elements of the heater plate, receive a signal indicative of a response to the characteristic energization signal, and determine a low water or out-of-water condition based on the magnitude and / or phase of the received signal indicative of the response to the energization signal.

[0253] In some configurations, the hardware controller may be configured to apply a characteristic energization signal to one or more heating elements of the heater plate, receive a signal indicative of a response to the characteristic energization signal, and determine a low water or out of water condition based on the magnitude and / or phase of the received signal indicative of the response to the energization signal.

[0254] In some configurations, a determined magnitude above a threshold may indicate a low water or out of water condition.

[0255] In some configurations, a determined magnitude and / or phase that meets a threshold may indicate a low water or out of water condition.

[0256] In some configurations, a determined magnitude and / or phase that is outside or within a predetermined region of the two-dimensional representation of the magnitude and / or phase can indicate a low water or out of water condition.

[0257] In some configurations, the size may be inversely proportional to the specific heat capacity of the humidifier chamber.

[0258] In some configurations, the hardware controller may be configured to apply a characteristic energization signal at a characteristic frequency.

[0259] In some configurations, the characteristic frequency can be higher than a normal operating frequency at which the hardware controller energizes one or more heating elements of the heater plate. In some configurations, the characteristic frequency can be higher than a heater plate control operating frequency at which the hardware controller energizes one or more heating elements of the heater plate.

[0260] In some configurations, the characteristic energization signal may be at least 1.5 times the normal operating frequency. In some configurations, the characteristic energization signal may be at least 1.5 times the heater plate control operating frequency.

[0261] In some configurations, the hardware controller may include a signal generator configured to generate and apply the characteristic energizing signal.

[0262] In some configurations, the hardware controller may be configured to apply the characteristic energization signal to the heater plate control signal. In some configurations, the characteristic energization signal may be applied by injection into the heater plate control signal. In some configurations, the hardware controller may be configured to apply the characteristic energization signal to a power control line that provides the heater plate control signal.

[0263] In some configurations, the hardware controller may include a filter that filters the signal indicative of the temperature of the heater plate to obtain a signal indicative of the response to the energization signal.

[0264] In some configurations, the filter may be a bandpass or highpass filter, hi some configurations, the filter may be a direct conversion receiver such as a homodyne, or an infinite impulse response filter.

[0265] In some configurations, the bandpass filter can filter the signal indicative of the temperature of the heater plate within a band corresponding to the frequency of the characteristic energization signal.

[0266] In some configurations, a signal magnitude indicating a heater plate temperature exceeding a threshold value at the frequency of the characteristic energization signal can indicate a low or out of water condition.

[0267] In some configurations, the received signal indicative of the temperature of the heater plate may include a frequency response of the signal indicative of the temperature of the heater plate, and the hardware controller is configured to determine a low water or out of water condition based on the frequency response.

[0268] In some configurations, the magnitude of the received signal indicative of the response to the characteristic energization signal may be processed to determine a score, and if the score is above a threshold, the score may indicate a low water or out of water condition.

[0269] In some configurations, the score may be determined by taking the squared or root-mean squared (RMS) temperature value of the received signal indicative of the response to the characteristic energization signal, smoothing the received signal indicative of the response to the characteristic energization signal by passing the received signal through a low-pass filter, and calculating the score.

[0270] In some configurations, the characteristic energization signal may include a cubed triangle wave, which may be applied by a pulse-width modulation (PWM) module of the hardware controller.

[0271] In some configurations, the characteristic energization signal may be a zero-mean signal.

[0272] In some configurations, the heater plate may include any of the example heater plate assemblies and multi-layer heater plate assemblies described above.

[0273] In some configurations, the system may include one or more features of the humidifier systems described above for use in medical procedures.

[0274] In some configurations, a method of detecting a low or depleted condition in a humidifier chamber of a respiratory or surgical humidifier system may include: determining a specific heat capacity value of the humidifier chamber using a hardware controller in a base unit of the respiratory or surgical humidifier system, the humidifier chamber defining a volume and capable of maintaining a water level, the humidifier chamber comprising a conductive base, the conductive base receivable on the base unit such that the conductive base contacts a heater plate of the base unit, the heater plate comprising one or more heating elements in electronic communication with the hardware controller and configured to be energized by the hardware controller; and determining the low or depleted condition based at least in part on the determined specific heat capacity value.

[0275] In some configurations, a method of detecting a low or depleted condition in a humidifier chamber of a respiratory or surgical humidifier system may include: using a hardware controller in a base unit of the respiratory or surgical humidifier system to determine a value from which a specific heat capacity of the humidifier chamber can be inferred, the humidifier chamber defining a volume and capable of maintaining a water level, the humidifier chamber including a conductive base, the conductive base being receivable on the base unit such that the conductive base contacts a heater plate of the base unit, the heater plate including one or more heating elements, the one or more heating elements being in electronic communication with the hardware controller and configured to be energized by the hardware controller; and determining the low or depleted condition based at least in part on the determined value from which the specific heat capacity can be inferred.

[0276] In some configurations, a determined specific heat capacity value below a threshold can indicate a low water or out of water condition. In some configurations, a determined value from which the specific heat capacity can be inferred below a threshold can indicate a low water or out of water condition.

[0277] In some configurations, the method may include continuously determining a specific heat capacity value. In some configurations, the method may include continuously determining a value from which the specific heat capacity can be inferred.

[0278] In some configurations, the method may include intermittently determining a specific heat capacity value. In some configurations, the method may include intermittently determining a value from which the specific heat capacity can be inferred.

[0279] In some configurations, the method may include determining the specific heat capacity value as a numerical score. In some configurations, the method may include determining a value from which the specific heat capacity can be inferred as a numerical score.

[0280] In some configurations, the respiratory or surgical humidifier system can include a temperature sensor coupled to or adjacent to the heater plate, the temperature sensor configured to determine the temperature of the heater plate.

[0281] In some configurations, the temperature sensor may include a thermistor.

[0282] In some configurations, the temperature sensor may include two thermistors, each acting as a voltage divider.

[0283] In some configurations, the method may include converting the temperature values ​​from the voltage readings of the two thermistors using a formula.

[0284] In some configurations, the method may include determining a specific heat capacity value based on a temperature reading of the temperature sensor. In some configurations, the method may include determining a value from which the specific heat capacity can be inferred based on a temperature reading of the temperature sensor.

[0285] In some configurations, the method may further include applying a characteristic energization signal to one or more heating elements of the heater plate, processing a filtered temperature signal from a temperature sensor corresponding to the characteristic energization signal, determining a specific heat capacity value based on the temperature signal, and outputting a low water or out of water warning in response to the determined specific heat capacity value being less than a threshold.In some configurations, the method may further include applying a characteristic energization signal to one or more heating elements of the heater plate, processing a filtered temperature signal from a temperature sensor corresponding to the characteristic energization signal, determining a value from which the specific heat capacity can be inferred based on the temperature signal, and outputting a low water or out of water warning in response to the determined value from which the specific heat capacity can be inferred being less than a threshold.

[0286] In some configurations, the method may include applying the characteristic energization signal continuously. In some configurations, the method may include applying the characteristic energization signal intermittently.

[0287] In some configurations, the method may include applying a characteristic energizing signal to a power control line that provides a heater plate control signal.

[0288] In some configurations, the characteristic energization signal may be applied to the heater plate control signal. In some configurations, the characteristic energization signal may be applied by being injected into the heater plate control signal.

[0289] In some configurations, the characteristic energization signal may be higher in frequency than the heater plate control signal.

[0290] In some configurations, the method may include passing the temperature measurement of the temperature sensor through a filter to pass the temperature measurement corresponding to the frequency of the characteristic energization signal. In some configurations, the method may include passing the temperature measurement of the temperature sensor through a bandpass filter having a filter frequency corresponding to the frequency of the characteristic energization signal to pass the temperature measurement corresponding to the frequency of the characteristic energization signal. In some configurations, the filter may be a highpass filter. In some configurations, the filter may be a direct conversion receiver such as a homodyne, or an infinite impulse response filter.

[0291] In some configurations, the method may include determining a specific heat capacity value using temperature measurements corresponding to the frequency of the characteristic energization signal. In some configurations, the method may include determining a value from which the specific heat capacity can be inferred using temperature measurements corresponding to the frequency of the characteristic energization signal.

[0292] In some configurations, the heater plate may include any of the example heater plate assemblies and multi-layer heater plate assemblies described above.

[0293] In some configurations, the system may include one or more features of the humidifier systems described above for use in medical procedures.

[0294] In some configurations, a non-transitory computer-readable medium stores computer-executable instructions that, when executed on a processing device, cause the processing device to perform a method.

[0295] In some configurations, a method of detecting a low or out-of-water condition in a humidifier chamber of a respiratory or surgical humidifier system may include applying a characteristic energization signal using a hardware controller in a base unit of the respiratory or surgical humidifier system to one or more heating elements of a heater plate in the base unit, the one or more heating elements of the heater plate being in electronic communication with the hardware controller and configured to be energized by the hardware controller, the respiratory or surgical humidifier system may further include a humidifier chamber, the humidifier chamber defining a volume and including a conductive base, the conductive base being receivable on the base unit such that the conductive base contacts the heater plate, the humidifier chamber being capable of holding a water level; receiving a signal indicative of a response to the characteristic energization signal from a temperature sensor coupled to or adjacent to the heater plate; and determining a low or out-of-water condition based on a magnitude of the received signal indicative of the response to the characteristic energization signal. In some configurations, the method may include determining a low water or out of water condition based on the magnitude and / or phase of a received signal indicative of a response to the characteristic energization signal.

[0296] In some configurations, a magnitude above a threshold can indicate a low or out of water condition. The magnitude can be inversely proportional to the specific heat capacity of the humidifier chamber.

[0297] In some configurations, a determined magnitude and / or phase that meets a threshold may indicate a low water or out of water condition.

[0298] In some configurations, a determined magnitude and / or phase that is outside or within a predetermined region of the two-dimensional representation of the magnitude and / or phase can indicate a low water or out of water condition.

[0299] In some configurations, the method may include applying a characteristic energizing signal to a power control line that provides a heater plate control signal.

[0300] In some configurations, the characteristic energization signal may be applied to the heater plate control signal. In some configurations, the characteristic energization signal may be applied by being injected into the heater plate control signal.

[0301] In some configurations, the method may include applying the characteristic energization signal continuously. In some configurations, the method may include applying the characteristic energization signal intermittently.

[0302] In some configurations, the method may include applying a characteristic energizing signal at a characteristic frequency.

[0303] In some configurations, the characteristic frequency can be higher than a normal operating frequency at which the hardware controller energizes one or more heating elements of the heater plate. In some configurations, the characteristic frequency can be higher than a heater plate control operating frequency at which the hardware controller energizes one or more heating elements of the heater plate.

[0304] In some configurations, the characteristic energization signal may be at least 1.5 times the normal operating frequency. In some configurations, the characteristic energization signal may be at least 1.5 times the heater plate control operating frequency.

[0305] In some configurations, the hardware controller may include a signal generator configured to generate and apply the characteristic energizing signal.

[0306] In some configurations, the hardware controller may include a filter that filters the signal indicative of the temperature of the heater plate to obtain a signal indicative of the response to the characteristic energization signal.

[0307] In some configurations, the filter may be a bandpass filter, in some configurations, the filter may be a highpass filter, in some configurations, the filter may be a direct conversion receiver such as a homodyne, or an infinite impulse response filter.

[0308] In some configurations, the bandpass filter can filter the signal indicative of the temperature of the heater plate within a band corresponding to the frequency of the characteristic energization signal.

[0309] In some configurations, a signal magnitude indicating a heater plate temperature exceeding a threshold value at the frequency of the characteristic energization signal can indicate a low or out of water condition.

[0310] In some configurations, the received signal may include a frequency response of the signal indicative of the temperature of the heater plate, and the hardware controller is configured to determine a low water or out of water condition based on the frequency response.

[0311] In some configurations, the method may include processing a magnitude of the received signal indicative of a response to the characteristic energization signal to determine a score, and if the score is above a threshold, the score may indicate a low water or out of water condition.

[0312] In some configurations, the method may include determining the score by obtaining a squared or root mean square (RMS) temperature value of the received signal indicative of the response to the characteristic energization, smoothing the received signal indicative of the response to the characteristic energization by passing the received signal through a low-pass filter, and calculating the score.

[0313] In some configurations, the characteristic energization signal may include a cubed triangle wave, which may be applied by a pulse width modulation (PWM) module of the hardware controller.

[0314] In some configurations, the characteristic energization signal may be a zero-mean signal.

[0315] In some configurations, the heater plate may include any of the example heater plate assemblies and multi-layer heater plate assemblies described above.

[0316] In some configurations, the system may include one or more features of the humidifier systems described above for use in medical procedures.

[0317] In some configurations, a non-transitory computer-readable medium stores computer-executable instructions that, when executed on a processing device, cause the processing device to perform a method.

[0318] These and other features, aspects, and advantages of the present disclosure will be described with reference to the drawings of certain embodiments which are intended to illustrate, in simplified form, particular embodiments and not to limit the disclosure. [Brief explanation of the drawings]

[0319] [Figure 1A] 1 illustrates a schematic diagram of an exemplary respiratory humidifier system. [Figure 1B] 1B illustrates a schematic diagram of an exemplary heater-based unit of the respiratory humidifier system of FIG. 1A. [Figure 1C] 1 illustrates a schematic diagram of an exemplary respiratory humidifier system. [Figure 1D] 1D illustrates a schematic diagram of an exemplary heater-based unit of the respiratory humidifier system of FIG. 1C. [Figure 1E] 1D schematically illustrates a partial view of the heater base unit of FIG. 1C and an exemplary breathing circuit heating element adapter. [Figure 2A] 1 illustrates a schematic diagram of an exemplary respiratory humidifier system having separate blower and heater-based units and connected to a nasal mask. [Figure 2B] 2B shows a schematic diagram of the respiratory humidifier system of FIG. 2A connected to a nasal cannula. [Figure 2C] 1 illustrates a schematic diagram of an exemplary respiratory humidifier system having an integrated blower unit and heater-based unit. [Figure 2D] 1 illustrates an exemplary surgical air delivery system. [Figure 2E] 1 illustrates an exemplary high flow therapy system. [Figure 3A] 1 shows a flowchart of an exemplary process for detecting a low and / or out-of-water condition in a humidifier chamber of a respiratory humidifier system. [Figure 3B] 1 shows a flowchart of an exemplary process for detecting a low and / or out-of-water condition in a humidifier chamber of a respiratory humidifier system. [Figure 3C] 10 shows a graph illustrating an exemplary feedback signal before and during a water out condition. [Figure 3D] 10 illustrates an exemplary feedback signal with and without a water out condition in the time domain. [Figure 3E] 10 illustrates an exemplary feedback signal with and without a water out condition in the frequency domain. [Figure 3F] 10 shows exemplary data points illustrating the magnitude and phase of the return signal, as well as exemplary water shortage classification boundaries based on the magnitude of the return signal. [Figure 3G] 10 shows exemplary data points illustrating the magnitude and phase of the feedback signal, as well as an exemplary water out classification boundary based on the phase of the feedback signal. [Figure 3H] 1 shows exemplary data points illustrating the magnitude and phase of the feedback signal, as well as two exemplary drainage classification boundaries based on the magnitude and phase of the feedback signal. [Figure 4A] 1 illustrates a flow diagram of an exemplary humidifier system for detecting low water and / or out of water conditions. [Figure 4B] 10 shows exemplary heater plate temperatures and output dew points before and during a water out condition in the time and frequency domains. [Figure 4C] 10 shows a graph illustrating an example waveform of a complementary signal for applying (e.g., injecting) to a heater plate power signal of a humidifier system. [Figure 4D] 4C shows a graph illustrating the harmonic content of the waveform of FIG. 4B. [Figure 4E] 1 illustrates an exemplary heater plate temperature transfer function for a humidifier system. [Figure 4F] 1 shows an exemplary waveform of the combined heater plate temperature and power signals, THP' and PHP'. [Figure 4G] 3B illustrates an exemplary band filter of the system diagram of FIG. 3A. [Figure 5A] 10 illustrates an exemplary algorithm for determining low and / or out of water conditions based on feedback signals. [Figure 5B] 1 shows exemplary drainage scores and dew points before and during a drainage condition. [Figure 6] 1 illustrates an exemplary leaky detector for determining the magnitude of a feedback signal. [Figure 7] 10 illustrates exemplary heater plate temperature signal gain and phase for different chambers and / or different flow rates. [Figure 8A] 1 illustrates an exemplary circuit model or system for detecting a low and / or empty water condition in a humidifier chamber. [Figure 8B] 1 illustrates an exemplary circuit model or system for detecting a low and / or empty water condition in a humidifier chamber. [Figure 8C] 8C illustrates an exemplary resistor-capacitor (RC) filter formed by the interaction between resistive and capacitive terms in the system of FIG. 8A or FIG. 8B. [Figure 8D] 10 illustrates clipping of an exemplary applied (eg, injection) waveform to detect low water and / or out-of-water conditions. [Figure 9] 1 illustrates an exploded view of an exemplary heater plate assembly. [Figure 9A] 1 illustrates an exploded view of another exemplary heater plate assembly. [Figure 9B] Various perspective views of the exemplary heater plate assembly of FIG. 9A are shown without the wires for connecting to a power source. [Figure 9C] Various perspective views of the exemplary heater plate assembly of FIG. 9A are shown without the wires for connecting to a power source. [Figure 9D]9B and 9C show cross-sectional views of the exemplary heater plate assembly of FIG. 9B. [Figure 9E] 1 illustrates a perspective view of a portion of an exemplary heater plate assembly. [Figure 10] 1A and 1B illustrate schematic diagrams of exemplary heater plate stacking configurations. [Figure 11] 10A and 10B illustrate schematic diagrams of another exemplary heater plate stacking configuration; [Figure 12A] 12 illustrates an exemplary three-dimensional representation of an upper heater plate in the heater plate stack configuration of FIG. 11. [Figure 12B] 12A-12C show various views of an exemplary three-dimensional representation of an upper heater plate in the heater plate stack configuration of FIG. 11; [Figure 12C] 12A-12C illustrate various views of an exemplary three-dimensional representation of an upper heater plate in the heater plate stack configuration of FIG. [Figure 12D] 12A-12C show various views of an exemplary three-dimensional representation of a bottom plate in the heater plate stack configuration of FIG. 11; [Figure 12E] 12A-12C show various views of an exemplary three-dimensional representation of a bottom plate in the heater plate stack configuration of FIG. 11; [Figure 12F] 12B-12C show bottom views of the upper heating plate. [Figure 12G] 12F shows a cross-sectional view of the upper heating plate of FIG. 12F along axis FF. [Figure 12H] 12F shows a side view, a top view, a bottom perspective view, a top perspective view, and a bottom view of the upper heating plate of FIG. 12F. [Figure 12I] 12F shows a side view, a top view, a bottom perspective view, a top perspective view, and a bottom view of the upper heating plate of FIG. 12F. [Figure 12J] 12F shows a side view, a top view, a bottom perspective view, a top perspective view, and a bottom view of the upper heating plate of FIG. 12F. [Figure 12K] 12F shows a side view, a top view, a bottom perspective view, a top perspective view, and a bottom view of the upper heating plate of FIG. 12F. [Figure 12L] 12F shows a side view, a top view, a bottom perspective view, a top perspective view, and a bottom view of the upper heating plate of FIG. 12F. [Figure 12M] 12F shows a side view, a top view, a bottom perspective view, a top perspective view, and a bottom view of the upper heating plate of FIG. 12F. [Figure 12N] 12K shows a top view, a top perspective view, a bottom view, and a side view of a lower plate configured for use with the upper heating plate of FIG. 12L. [Figure 12O] 12K shows a top view, a top perspective view, a bottom view, and a side view of a lower plate configured for use with the upper heating plate of FIG. 12L. [Figure 12P] 12K shows a top view, a top perspective view, a bottom view, and a side view of a lower plate configured for use with the upper heating plate of FIG. 12L. [Figure 12Q] 12K shows a top view, a top perspective view, a bottom view, and a side view of a lower plate configured for use with the upper heating plate of FIG. 12L. [Figure 12R] 12K shows a top view, a top perspective view, a bottom view, and a side view of a lower plate configured for use with the upper heating plate of FIG. 12L. [Figure 13A] 1 illustrates a schematic of the operation of a thermal interface material. [Figure 13B] 1 illustrates a schematic of the operation of a thermal interface material. [Figure 13C] 1 illustrates a schematic of the operation of a thermal interface material. [Figure 13D] 1 illustrates a schematic of the operation of a thermal interface material. [Figure 14] 1A and 1B illustrate schematic diagrams of exemplary heater plate stacking configurations. [Figure 15] 1A and 1B illustrate schematic diagrams of exemplary heater plate stacking configurations. [Figure 16A] 1A and 1B schematically illustrate first and second side views of an exemplary heating element. [Figure 16B] 1A and 1B schematically illustrate first and second side views of an exemplary heating element. [Figure 17A] 16A-16C show various views of an exemplary three-dimensional representation of an upper heater plate in the heater plate stack configuration of FIG. 15. [Figure 17B]16A-16C show various views of an exemplary three-dimensional representation of an upper heater plate in the heater plate stack configuration of FIG. 15. [Figure 17C] 16A-16C show various views of an exemplary three-dimensional representation of an upper heater plate in the heater plate stack configuration of FIG. 15. [Figure 17D] 16A-16C show various views of an exemplary three-dimensional representation of an upper heater plate in the heater plate stack configuration of FIG. 15. [Figure 17E] 16A-16C show various views of an exemplary three-dimensional representation of an upper heater plate in the heater plate stack configuration of FIG. 15. [Figure 18A] 16A-16C show various views of an exemplary three-dimensional representation of a bottom plate in the heater plate stack configuration of FIG. 15. [Figure 18B] 16A-16C show various views of an exemplary three-dimensional representation of a bottom plate in the heater plate stack configuration of FIG. 15. [Figure 18C] 16A-16C show various views of an exemplary three-dimensional representation of a bottom plate in the heater plate stack configuration of FIG. 15. [Figure 18D] 16A-16C show various views of an exemplary three-dimensional representation of a bottom plate in the heater plate stack configuration of FIG. 15. [Figure 18E] 16A-16C show various views of an exemplary three-dimensional representation of a bottom plate in the heater plate stack configuration of FIG. 15. [Figure 18F] 16A-16C show various views of an exemplary three-dimensional representation of a bottom plate in the heater plate stack configuration of FIG. 15. [Figure 19A] 10A-10C show various views of another exemplary bottom plate. [Figure 19B] 10A-10C show various views of another exemplary bottom plate. [Figure 19C] 10A-10C show various views of another exemplary bottom plate. [Figure 19D] 10A-10C show various views of another exemplary bottom plate. [Figure 19E] 10A-10C show various views of another exemplary bottom plate. [Figure 19F] 10A-10C show various views of another exemplary bottom plate. [Figure 20A]19A-19F show bottom views of a heater plate assembly incorporating the exemplary bottom plate of FIGS. 19A-19F. [Figure 20B] 20B shows various cross-sectional views of the heater plate assembly of FIG. 20A. [Figure 20C] 20B shows various cross-sectional views of the heater plate assembly of FIG. 20A. [Figure 21A] 10A-10C show various views of another exemplary bottom plate. [Figure 21B] 10A-10C show various views of another exemplary bottom plate. [Figure 21C] 10A-10C show various views of another exemplary bottom plate. [Figure 21D] 10A-10C show various views of another exemplary bottom plate. [Figure 21E] 10A-10C show various views of another exemplary bottom plate. [Figure 21F] 10A-10C show various views of another exemplary bottom plate. [Figure 22A] 21A-21F show various cross-sectional views of a heater plate assembly incorporating the exemplary bottom plate of FIGS. 21A-21F. [Figure 22B] 21A-21F show various cross-sectional views of a heater plate assembly incorporating the exemplary bottom plate of FIGS. 21A-21F. DETAILED DESCRIPTION OF THE INVENTION

[0320] While specific embodiments and examples are described below, those skilled in the art will recognize that the present disclosure extends beyond the specifically disclosed embodiments and / or uses and obvious modifications and equivalents thereof. Accordingly, it is intended that the scope of the disclosure disclosed herein should not be limited by any specific embodiments described below. For example, the dimensions provided in this disclosure are examples and not limitations.

[0321] Exemplary Respiratory Humidifier System This disclosure provides examples of respiratory or surgical humidifier systems configured to deliver humidified and / or heated gas to a patient or user in multiple modes. The modes may include at least an invasive mode (e.g., for patients with bypassed airways or laparoscopic surgery) and a non-invasive mode (e.g., for patients or users wearing respiratory masks). Each mode may have a personalized humidity output, which may be expressed as a dew point output setpoint. For example, a user may select a setpoint that may indicate the operating mode. The non-invasive mode may have a setpoint of 31 degrees Celsius, 29 degrees Celsius, 27 degrees Celsius, or other setpoint. The invasive mode may have a setpoint of 37 degrees Celsius or other setpoint. Some respiratory humidifier systems disclosed herein may also include a high-flow, non-sealing mode or any other mode known to those skilled in the art. The high-flow, non-sealing mode (referred to herein as Optiflow® mode) is commercially available as Optiflow® by Fisher and Paykel Healthcare Limited, Auckland, New Zealand.

[0322] 1A and 1C, an exemplary respiratory humidification system 100, 101 may include a heater base unit 102 having a heater plate 120 (see FIGS. 1B and 1D). The heater plate 120 may include one or more heating elements. The heater base unit 102 may have a housing and a controller (e.g., a microprocessor) contained within the housing for controlling the supply of energy to the heating elements.

[0323] The humidifier heater plate 120 may have a temperature sensor (see temperature sensor 262 in FIG. 2A ) (e.g., a temperature transducer, a thermistor, or other type of temperature sensor). Multiple different temperature sensors may also be used. The temperature sensor may measure the temperature of the heater plate 120. The temperature sensor may be in electrical communication with a controller in the heater base unit 102 so that the controller can monitor the temperature of the heater plate 120. Measurements produced by the temperature sensor may be used as input for the low and / or out of water detection process described below.

[0324] The temperature sensor may also include two or more thermistors. Each thermistor may function as a voltage divider. The average of the readings of the two thermistors may be used as an input for the low and / or out-of-water detection process. More than two thermistors may also be used for redundancy. Additional thermistors may also be included. The temperature sensor is located on the lower surface of the heater plate. The temperature sensor may preferably be located on the upper heating plate of the heater plate assembly. The upper heating plate is the plate that contacts the humidifier chamber. The heater plate 120 herein may refer to the upper heating plate that is exposed and positioned to contact the base of the humidifier chamber when the humidifier chamber is placed in its operating position on the heater base. The temperature sensor may be located on the edge of the heater plate or substantially in the center of the heater plate. The heating element used is a nichrome wire or other type of heating filament wound around an electrical insulator block or core. The heater plate may include multiple layers of electrical insulation. The heater plate may include a rear plate or a bottom plate with multiple pieces screwed or bolted together. Further details of examples of heater plates suitable for practicing the techniques disclosed herein are described below with reference to Figures 8A-18F. Alternatively, the heater plate may include multiple layers that may be laminated or glued together to form a unitary heater plate. In a further alternative configuration, the heater plate may be formed on a semiconductor by etching or deposition or any suitable configuration.

[0325] The humidifier chamber 103 may be removably received and held on the heater base unit 102 such that the humidifier chamber base is positioned in contact with the heater plate 120 within the heater base unit 102. Referring to FIGS. 1B and 1D, which illustrate examples of the heater base unit 102 of FIGS. 1A and 1C, respectively, the humidifier base 102 may have a collar 124 for engaging with a flange of the humidifier chamber 103, as shown in FIGS. 1A and 1C. The collar 124 defines a lip that engages with the flange of the humidifier chamber 103 to hold the humidifier chamber 103 in an operative position on the heater base 102. The humidifier chamber 103 may include a conductive base. When engaged with the heater base unit 102, the conductive base of the humidifier chamber 103 may contact the heater plate 120, such as the top surface of the upper heating plate of the heater plate 120. When a power signal is sent to the heating element, energizing the heating element heats the water in chamber 103. Chamber 103 may also be connected to a water source 142 (FIG. 1C). Water source 142 may add water to chamber 103 when the water in chamber 103 is low or completely depleted. The addition of water may be performed manually or controlled by a controller, such as upon an alert from system 101 that a low or depleted water condition may exist.

[0326] Continuing with reference to FIGS. 1A and 1C, the gas to be humidified may include one or more of air, oxygen, anesthetic, other auxiliary gases, or any mixture of gases. Gas may be supplied to the humidifier chamber 103 via a gas inlet 104, which may be connected to a gas source such as a ventilator, a CPAP blower in the case of CPAP therapy, or a remote source. In high-flow therapy, the gas may be supplied by a blower, or alternatively, a wall source with a flow and / or pressure regulator. The humidifier chamber 103 may also include a gas outlet 105, which may be connected to a breathing circuit 106. The breathing circuit 106 may deliver the humidified and heated gas to a patient or user. As shown in FIG. 1A, the patient end 107 of the breathing circuit 106 may be connected to a patient interface, such as a nasal cannula 113 or a nasal mask 114. The breathing circuit 106 may also be connected to other types of patient or user interfaces, such as a full-face mask, an endotracheal tube, or others. The breathing circuit 106 of FIG. 1C may also be connected to any suitable patient interface disclosed herein.

[0327] A heating element 110 (e.g., one or more heater wires) may be provided in the breathing circuit 106. The heating element 110 may help prevent condensation of the humidified gas within the breathing circuit 106. The heating element 110 may also be in electrical communication with a controller within the heater base unit 102. As shown in FIGS. 1C and 1E, a breathing circuit heating element adapter cable 128 may have two connectors at two ends of the cable 128 for coupling the heating element 110 to the heater base unit 102 (e.g., a controller of the heater base unit 102). The heating element adapter cable 128 may facilitate a simple connection between the heating element 110 and the heater base unit 102. The heating element 110 is controlled by a control unit, including control of power to the heating element 110 by the control unit. The heating element 110 within the breathing circuit 106 reduces condensation and also ensures that the temperature of the gas is maintained within a predetermined range. The heating element adapter cable 128 may also include an ambient temperature sensor 126. The ambient temperature sensor 126 can enable the system 101 to adjust the power of the heating element 110 to compensate for the ambient temperature or changes in ambient temperature. A heating element indicator 130 can be embedded in the connector that connects to the heater base unit 102. The heating element indicator 130 can illuminate when a properly functioning heating element 110 is connected to the heater base unit 102. When the heating element indicator 130 is illuminated, the system 101 can heat the gas in the breathing circuit 106 via the heating element 110 to minimize condensation, in addition to heating the gas passing through the humidifier chamber 103 via the heater plate 120. If the heating element 110 is malfunctioning or not connected, or if the heating element indicator 130 is not illuminated, the system 101 may heat the gas only by heating the water in the chamber 103 via the heater plate 120. Alternatively, the heating element indicator 130 may illuminate if there is a fault or break in the adapter cable 128. The illuminated indicator 130 may function as a visual message or a visual warning. The indicator 130 may not be illuminated if the heating element 110 is functioning properly.

[0328] The controller of the respiratory humidifier system 100, 101 can control at least the heater plate 120, and preferably or optionally, the heating element 110, without additional sensors (e.g., in the humidifier chamber, the breathing circuit, and / or elsewhere in the system). This can be achieved by estimating the flow rate of gas within the respiratory humidifier system 100, 101 using parameters already available to the controller. For a given respiratory humidifier system, the controller can determine the appropriate power level to apply to the heater plate 120. Applying power to the heater 120 can generate humidity and heat the gas. The power applied to the heater plate can be at a rate that generates a predetermined amount of humidity. Furthermore, the controller may also be able to use the parameters to provide a more appropriate power level to the heating element 110. As shown in FIGS. 1C and 1E, the system 101 can also include an ambient temperature sensor 126. The ambient temperature sensor can be located anywhere exposed to ambient air. For example, the system 101 may include an ambient temperature sensor 126 on the heating element adapter cable 128 .

[0329] As shown in FIG. 1E , the front panel of the heater-based unit 102 may include multiple user controls and indicators, such as a power button 132, a humidity setting push button 134, and multiple (e.g., three, four, five, or more) humidity setting indicators 136 (which may include LED lights) adjacent to the humidity setting push button 134. The location, shape, and size of the user controls and indicators are not limited. There may be four available humidity setting levels, indicated by the four humidity setting indicators 136. The four humidity settings may correspond to different types of therapy provided to the patient. For example, a maximum amount of humidity may be selected when the humidifier is operating in an invasive therapy mode. A minimum amount of humidity may be applied in a low-flow oxygen therapy mode. The amount of humidity may be selected or predetermined based on the therapy requirements or type of therapy. Alternatively, the humidifier 100, 101 may include a controller configured to automatically select the amount of humidity to be delivered based on the therapy mode, the patient, or the type of therapy applied to the patient. Optionally, the humidifier 100, 101 may include a touchscreen that can communicate information to a user. The touchscreen may also be configured to receive input from a user.

[0330] The humidity level can be adjusted by pressing a humidity setting push button 134, which can also be a momentary push button. The front panel can also include multiple alarm indicators 138 (which can include LED lights) to indicate the following non-limiting example conditions: "out of water" condition (including low water and out of water), heating element adapter not connected, audible alarm muted, and a "see manual" display value used to indicate that a fault has occurred within the system 101.

[0331] System 101 may be suitable for providing respiratory therapy for different purposes, such as critical care (e.g., in a hospital) and home care. System 101 is suitable for providing non-invasive, high-flow therapy to both adult and pediatric patients.

[0332] As described in detail below, the controller of the respiratory humidifier system 100, 101 can also use input from a temperature sensor to determine low water and / or out-of-water conditions in the humidifier chamber. The controller may not require input from additional sensors for out-of-water detection. Requiring only one sensor reduces the cost of the respiratory humidifier system 100, 101 and / or allows the respiratory humidifier system 100, 101 to be simpler and lighter than respiratory humidifier systems with multiple sensors. As described below, the system 101 is also configured to improve thermal coupling within the system and enable out-of-water detection at lower power levels, which may include low flow rates, low humidity, or no chamber. The described assembly improves thermal coupling, i.e., improves thermal conductivity between elements of the heater plate assembly components, so that generated heat is transferred to the upper heater plate and detected by the thermistor.

[0333] The low water and / or out-of-water detection methods and systems disclosed herein can also be incorporated into other types of respiratory humidifier systems disclosed herein, which may include more than one sensor and / or have different configurations. As shown in FIGS. 2A and 2B , respiratory humidifier system 200 can include a blower unit 203. Blower unit 203 can have an internal compressor unit, flow generator, or fan unit 213. Air from the atmosphere can enter the housing of blower unit 203 through atmospheric inlet 240 and be drawn through fan unit 213. The output of fan unit 213 is adjustable so that the fan speed is variable. A pressurized gas flow can exit fan unit 213 and blower unit 203 and travel to humidifier chamber 205 through connecting conduit 204. The pressurized gas flow can enter humidifier chamber 205 through inlet port 223.

[0334] The blower unit may also be replaced by a ventilator having a fan or turbine configured to generate airflow. The ventilator may receive gas from a compressed air source, such as a tank. The ventilator may also use one or more valves to control the delivery of air to the humidifier chamber 205.

[0335] 2B or 2C, the respiratory humidifier system 200 can also provide oxygen (O2) or an O2 fraction to the user. The system 200 can receive O2 from a remote source and / or by blending incoming O2 from a remote source with ambient air. The blending of ambient air with incoming O2 can occur via a venturi or similar inlet located within the control unit 203.

[0336] Figure 2C shows an exemplary respiratory humidifier system 200 having an integrated blower / heater-based unit 210. The system of Figure 2C operates in a similar manner to the respiratory humidifier system 200 shown in Figures 2A and 2B, except that the heater-based unit is integrated with the blower, forming the integrated unit 210 together with the housing 203.

[0337] Similar to the humidifier chamber 103 described above, the humidifier chamber 205 of FIGS. 2A-2C can contain a volume of water 220. In use, the humidifier chamber 205 can be engaged with a heater base unit 221 or an all-in-one unit 210 (e.g., by contacting and / or being placed on top of a heater plate 212). The heater plate 212 is powered to heat the conductive base of the humidifier chamber 205, thereby heating the contents within the humidifier chamber 205 (e.g., the volume of water 220). A gas stream entering the humidifier chamber 205 through the inlet port 223 is heated and humidified and can exit the humidifier chamber 205 through the outlet port 209 and enter the breathing circuit 206.

[0338] The heated and humidified gases pass along the length of the respiratory conduit 206 and may be delivered to the patient or user 202 via a user interface 207. The respiratory conduit 206 may also be capable of being heated via a heating element (such as a heater wire 210) to help prevent condensation of the heated and humidified gases. The user interface 207 shown in Figures 2A and 2C is a nasal mask that surrounds and covers the nose of the user 202. However, a nasal cannula (as shown in Figure 2B), a full face mask, an endotracheal tube, a tracheostomy fitting, or any other suitable user interface could replace the nasal mask shown.

[0339] The central controller or control system may be located within blower unit 203 (controller 208a), heater-based unit 221 (controller 208b), or both (e.g., having separate blower controller 208a and humidifier controller 208b in electrical communication with each other via a connecting cable or otherwise, or central controller 208 as shown in FIG. 2C). Blower controller 8a and humidifier controller 8b may be capable of being in a master-servant relationship (e.g., one of the controllers can control the functions of the other) or a peer relationship (e.g., each controller can function independently of the other). For example, humidifier controller 208b may be a standalone unit configured for use with any type of gas supply.

[0340] The control system may receive user input via user controls 211 located on the heater base unit 221, the blower unit 202, or both. The control system may also receive input from sensors located at various locations throughout the system 200. Similar to the respiratory humidifier system 100 described above, the respiratory humidifier system 200 may include a heater plate temperature sensor 262 located adjacent to or at (e.g., directly below) the heater plate 212. The heater plate temperature sensor 262 may be configured to measure the temperature of the heater plate 212.

[0341] As shown in FIGS. 2A-2C, the respiratory humidifier system 200 may have additional temperature sensors. The humidifier of FIG. 2A may include an ambient temperature sensor 260. The ambient temperature sensor 260 may be located within, near, or on the housing of the blower unit 203, or elsewhere, for example, downstream of the fan unit 213 and / or in the gas stream closer to the inlet 223 of the humidifier chamber 205. The ambient sensor may be located adjacent to the inlet of the tubing or may be coupled to a heater wire or heater wire adapter connected to the heater base by a flying lead adapter. The ambient temperature sensor 260 may be configured to measure the temperature of the incoming air from the atmosphere. An outlet temperature sensor may be located at or near the humidifier chamber exit port 209 or at the chamber end (opposite the patient or user end) of the breathing circuit 206. The outlet temperature sensor may be configured to measure the temperature of the gas stream exiting the humidifier chamber 205. Measurements produced by the outlet temperature sensor may also be able to be used as input to the low water and / or out of water detection process. The patient or user end temperature sensor 215 may be located at the patient or user end of the breathing circuit 206. The patient or user end temperature sensor 215 may also be able to be located in or on the patient or user interface 207.

[0342] The respiratory humidifier system 200 may include a flow sensor configured to measure gas flow within the system 200. The flow sensor may be located upstream of the fan unit 213, downstream of the fan unit 213, or elsewhere. For example, the flow sensor 263 may be located at or near the humidifier chamber outlet 209, at the chamber end of the breathing circuit 206, and / or adjacent to an outlet temperature sensor. The sensor 263 may be capable of including both a temperature sensor and a flow sensor. The controllers 208a, 208b may also include one or more other sensors 250, 280, 290 capable of measuring humidity, temperature, pressure, flow rate, and / or other characteristics of the gas flow.

[0343] In response to user input from the control 211 and / or input signals received from sensors, the control system can determine one or more control outputs that can send signals to adjust the power to the heater plate 212, the speed of the fan unit 213, and / or the like.

[0344] In any of the above-described respiratory humidifier systems 100, 200, a temperature probe may also be placed within the volume of water in the humidifier chamber. Additionally and / or alternatively, a non-contact temperature sensor (such as an infrared sensor) may also be used to measure the temperature of the heater plate and / or contents of the humidifier chamber, and / or the temperature of the gas path.

[0345] The readings of a temperature probe, non-contact temperature sensor, and / or any other temperature sensor located downstream of the gas inlet of the humidifier chamber and / or near the heater plate may also be used as inputs to the low water and / or out of water detection process described below.

[0346] FIG. 2D schematically illustrates the use of an exemplary air insufflation system 1 during a medical procedure. The surgical humidification system humidifies a surgical cavity (e.g., pneumoperitoneum). The humidifier can humidify tissue within the surgical cavity to prevent tissue damage due to dehydration or dryness, including low temperatures. As shown in FIG. 2D, patient 2 may have a cannula 207 inserted into a cavity of patient 2 (e.g., patient 2's abdomen in the case of laparoscopic surgery).

[0347] As shown in FIG. 2D , a cannula 207 may be connected to a gas delivery conduit 206 (e.g., via a Luer lock connector 4). The cannula 207 may be used to deliver gas to a surgical site, such as within a cavity of a patient 2. The cannula 207 may include one or more passageways for introducing gas and / or one or more surgical instruments into the surgical cavity. The surgical instrument may be a scope, an electrocautery tool, or any other instrument. The surgical instrument may be coupled to an imaging device, which may have a screen. The imaging device may be part of a surgical stack, which may include multiple surgical instruments and / or devices.

[0348] The surgical gas delivery system may also include a drain cannula. The drain cannula may have substantially the same features as cannula 207. The drain cannula may include a valve to allow drainage. The valve may be automatically controlled by a controller associated with the gas source (i.e., the insufflator) or by a controller within the humidifier. The valve may also be manually activated (e.g., by turning a stopcock by hand, foot pedal, or other means). The drain cannula may be coupled to a filtration system to filter smoke, etc. Alternatively, the drain cannula may also be coupled to a recirculation system configured to recirculate gas from the surgical cavity to the insufflator for redelivery to the surgical cavity. The gas may be filtered and / or dehumidified before being returned to the insufflator. In certain configurations, the cannula may include two or more passageways. One passageway may be configured to deliver gas and / or medical devices to the surgical cavity. Another passageway may be configured to evacuate gas from the surgical cavity. The evacuation passageway may include a valve and / or a passive evacuation opening. The cannula 207 may also include a retention feature (such as a rib) to hold the medical instrument (such as a scope) in a substantially concentric orientation relative to the delivery passageway.

[0349] The gas delivery conduit 206 may be made of flexible plastic and may be connected to the humidifier chamber 205 at the inlet port 223. Optionally or preferably, the humidifier chamber 205 may be connected in series to the gas supply 9 via a further conduit 204. The gas supply or gas source may be an insufflator, bottled gas, or a wall gas source. The gas supply 9 may provide gas without humidification and / or heating. A filter 6 may be connected downstream of the humidifier outlet 209. A filter may also be located along the further conduit 209 or at the inlet of the cannula 205. The filter may be configured to filter out pathogens and particulate matter to reduce infection or contamination of the surgical site by the humidifier or gas source. The gas supply may provide a continuous or intermittent flow of gas. The further conduit 204 may also preferably be made of flexible plastic tubing.

[0350] The gas supply 9 can provide one or more insufflation fluids, including carbon dioxide, to the humidifier chamber 205. The gas supply can provide a continuous or intermittent flow of gas. The gas can be humidified as it passes through the humidifier chamber 205, which can contain a volume of water 220. In some configurations, the gas supply can be connected directly to the cannula 205 without a humidifier unit.

[0351] A humidifier incorporating the humidifier chamber 205 can be any type of humidifier. The humidifier chamber 205 can include a chamber formed of plastic having a metal or other conductive bottom sealed thereto. During use, the bottom can be in contact with a heater plate 212. A quantity of water 220 contained within the chamber 205 can be heated by the heater plate 212. The heater plate 212 can be under the control of a humidifier controller or control means 208. The quantity of water 220 within the chamber 205 can be heated to vaporize, causing the water vapor to mix with the gas flowing within the chamber 205 and heat and humidify the gas.

[0352] The controller or control means 208 may be housed within the humidifier base unit 221. The humidifier base unit 221 may also house the heater plate 212. The heater plate 212 may have an electric heating element within it or in thermal contact with it. One or more insulating layers may be located between the heater plate 221 and the heater element. The heater element may be a base element (or core) with wire wound around it. The wire may be nichrome wire (or nickel-chromium wire). The heater element may also include a multilayer substrate with heating tracks electrodeposited or etched. The controller or control means 208 may include electronic circuitry, which may include a microprocessor, for controlling the supply of energy to the heating element. The humidifier base unit 221 and / or the heater plate 212 may be removably engageable with the humidifier chamber 205. Alternatively or additionally, the humidifier chamber 205 may also include a built-in heater.

[0353] The heater plate 212 may include a temperature sensor, temperature transducer, etc., which may be electrically connected to the controller 208. The heater plate temperature sensor may be located in the humidifier base unit 221. The controller 221 may monitor the temperature of the heater plate 212, thereby estimating the temperature of the water 220.

[0354] A temperature sensor may also be located at or near the outlet 209 to monitor the temperature of the humidified gas exiting the humidifier chamber 205 through the outlet 209. The temperature sensor may also be connected (e.g., by cable or wirelessly) to the controller 208. Additional sensors may also be incorporated to detect properties of the gas (temperature, humidity, flow, etc., or other) at the patient end of the gas delivery conduit 206, for example.

[0355] Gas may exit through the humidifier outlet 209 and enter the gas delivery conduit 206. The gas may pass through the gas delivery conduit 206 and enter the surgical cavity of the patient 2 via the cannula 207, thereby expanding the cavity and maintaining intracavity pressure. Preferably, the gas exiting the humidifier chamber 205 outlet 209 may have a relative humidity of up to 100%, for example, about 100%. As the gas travels along the gas delivery conduit 206, "additional condensation" may occur, causing water vapor to condense on the walls of the gas delivery conduit 206. Additional condensation may have undesirable effects, such as adversely reducing the moisture content of the gas delivered to the patient. To reduce and / or minimize the occurrence of condensation within the gas delivery conduit 206, a heater wire 210 may be provided within, throughout, or around the gas delivery conduit 206. To power the heater wire, the heater wire 210 can be electronically connected to a humidifier base unit 221, for example, by an electrical cable 219. The cable 219 can be similar to the heater wire adapter cable including the ambient sensor described in FIGS. 1D and 1E. Alternatively, the humidifier can be integrated with the insufflator of the surgical humidification system in a common housing. The humidifier and insufflator can be controlled by a single controller. The surgical humidification system can also include a recirculation system configured to recirculate gas from the surgical site and rehumidify the gas. The recirculation system can include a smoke filter and a scrubber for scrubbing out the gas. The recirculation system can also include a device for removing humidity or condensation from the recirculated gas.

[0356] The heater wire 210 may include insulated copper alloy resistance wire, other types of resistance wire, or other heater elements, and / or may be made of any other suitable material. The heater wire may be a straight or spirally wound element. An electrical circuit including the heater wire 210 may be located within the wall of the gas delivery tube 206. The gas delivery tube 206 may be a spirally wound tube. The heater wire 210 may be spirally wound around an insulating core of the gas delivery conduit 206. The insulating coating around the heater wire 210 may include a thermoplastic material. When heated to a predetermined temperature, the thermoplastic material may be in a state where it can change its shape, and upon cooling, the new shape may be substantially elastically retained. The heater wire 210 may be wound into a single or double helix. Measurements by the temperature sensor at the patient end of the conduit 206 and / or additional sensors can provide feedback to the controller 208 so that the controller 208 can energize the heater wire to increase and / or maintain the temperature of the gas in the gas delivery conduit 206 so that the gas delivered to the patient is at or near 37°C (e.g., about 35°C to about 45°C).

[0357] The controller or control means 208 may include, for example, a microprocessor or logic circuit with associated memory or storage means capable of holding a software program. When executed by the control means 208, the software may control the operation of the air delivery system 1 according to the instructions set therein and / or in response to external inputs. For example, the heater plate 212 may provide input to the controller or control means 208, providing the controller or control means 208 with information regarding the temperature and / or power usage of the heater plate 212. The controller or control means 208 may provide an input of the temperature of the gas stream. For example, a temperature sensor may provide an input indicating the temperature of the humidified gas stream as the gas exits the outlet 209 of the humidifier chamber 205. A flow sensor may also be provided at or near the same location as the temperature sensor or at another suitable location within the air delivery system 1. Alternatively, the system may include only a temperature sensor. The controller 208 may control a flow regulator, which regulates the flow of gas through the system 1. The flow regulator may include a flow inducer and / or inhibitor, such as an electrically powered fan. Additionally or alternatively, valves and / or vents may be used to control the flow rate of the gas.

[0358] A patient input located on the humidifier base unit 221 can allow a user (such as a surgeon or nurse) to set the desired gas temperature and / or gas humidity level to be delivered. Other functions may also be controllable by user input, such as control of the heating delivered by the heater wire 210. The controller 208 can control the system 1, and in particular, the flow rate, temperature, and / or humidity of the gas delivered to the patient, as appropriate for the type of medical procedure for which the system 1 is being used.

[0359] The humidifier base unit 221 may also include a display for displaying to the user the characteristics of the gas flow being delivered to the patient 2 .

[0360] Although not shown, the humidifier may also be a pass-over humidifier, which may include a chamber with a volume of water or any other type of humidifying fluid, but may not include a heater plate for heating the water. The chamber may be in fluid communication with a gas supply such that the insufflation gas is humidified by water vapor transferred from the volume of water as it passes over the volume of water.

[0361] The humidifier of the surgical humidifier system of Figure 2D can incorporate any of the features of the humidifier unit 221 and humidification chamber 205 shown in Figure 2A.

[0362] In use, the humidifiers described above can be located outside the "operating sterile zone" and / or adjacent to the insufflator. As a result, medical personnel do not need to touch the humidifier when moving cannulas to manipulate medical instruments within the surgical cavity during surgery. The humidifier may not need to be as sterilized as the medical instruments. Furthermore, a humidifier located outside the "operating sterile zone" reduces obstacles to medical personnel that may restrict their and / or medical instrument movement within an already crowded space during a surgical procedure.

[0363] FIG. 2E provides a schematic diagram of a high-flow therapy system 10. The system 10 may include a main device housing 100. The main device housing 100 may house a flow generator 11, which may be in the form of a motor / impeller configuration, a humidifier or humidification chamber 12, a controller 13, and a user interface 14. The user interface 14 may include a display and input devices such as buttons, a touchscreen, a combination of a touchscreen and buttons, etc. The controller 13 may include one or more hardware and / or software processors and may be configured or programmed to control the components of the device. Control includes, but is not limited to, operating the flow generator 11 to generate a flow of gas for delivery to the patient, operating the humidifier 12 to humidify and / or heat the gas flow, receiving user input from the user interface 14 for reconfiguration and / or user-defined operation of the respiratory system 10, and outputting information to a user (e.g., on a display). The user may be a patient, a medical professional, or others.

[0364] 2E, the patient breathing conduit 16 may be coupled to the gas outlet 21 of the main device housing 100 of the respiratory system 10 and may be coupled to a patient interface 17, such as a non-sealing interface, such as a nasal cannula having a manifold 19 and nasal prongs 18. The patient breathing conduit 16 may also be coupled to a face mask, nasal mask, nasal pillow mask, endotracheal tube, tracheostomy interface, or the like.

[0365] The gas flow may be generated by a flow generator 11 and may be humidified before being delivered to the patient through a patient conduit 16 and via a patient interface 17. A controller 13 may control the flow generator 11 to generate a gas flow at a desired rate and / or may control one or more valves to control the mixture of air and oxygen or other breathable gas. The controller 13 may control a heating element in the humidification chamber 12 to heat the gas to a desired temperature to reach a desired level of temperature and / or humidity for delivery to the patient. The patient conduit 16 may have a heating element 16a, such as a heater wire, for heating the gas flow passing to the patient. The heating element 16a may also be under the control of the controller 13.

[0366] The system 10 may use ultrasonic transducers, flow sensors such as thermistor flow sensors, pressure sensors, temperature sensors, humidity sensors, or other sensors in communication with the controller 13 to monitor gas flow characteristics and / or operate the system 10 in a manner that provides appropriate therapy. Gas flow characteristics may include gas concentration, flow rate, pressure, temperature, humidity, or others. Sensors 3a, 3b, 3c, 20, 25, such as pressure sensors, temperature sensors, humidity sensors, and / or flow sensors, may be located at various locations within the main device housing 100, the patient conduit 16, and / or the patient interface 17. The controller 13 may receive output from the sensors and assist the respiratory system 10 in operating in a manner that provides appropriate therapy, such as to determine appropriate target temperatures, flow rates, and / or pressures for the gas flow. Providing appropriate therapy may include meeting the patient's inspiratory demand.

[0367] System 10 may include a wireless data transmitter and / or receiver or transceiver 15 to enable controller 13 to wirelessly receive data signals 8 from the motion sensors and / or control various components of system 10. Additionally or alternatively, data transmitter and / or receiver 15 may deliver data to a remote server or enable remote control of system 10. System 10 may include a wired connection, using, for example, a cable or wire, to enable controller 13 to receive data signals 8 from the motion sensors and / or control various components of system 10.

[0368] The flow therapy device 10 may include a high-flow therapy device. High-flow therapy, as described herein, shall be given its typical and ordinary meaning as understood by those skilled in the art and generally refers to a respiratory assistance system that delivers a target flow rate of humidified respiratory gas through an intentionally unsealed patient interface, generally at a rate intended to meet or exceed the patient's inspiratory flow. Exemplary patient interfaces include, but are not limited to, nasal or tracheal patient interfaces. Typical flow rates for adults often range from about 15 liters per minute to greater than about 60 liters per minute. Typical flow rates for pediatric patients (such as neonates, infants, and children) often range from about 1 liter per minute per kilogram of patient weight to greater than about 3 liters per minute per kilogram of patient weight, but are not limited to these. High-flow therapy may also include the administration of a mixed gas composition containing supplemental oxygen and / or a therapeutic agent. High-flow therapy is often referred to as nasal high flow (NHF), humidified high flow nasal cannula (HHFNC), high flow nasal oxygen (HFNO), high flow therapy (HFT), or tracheal high flow (THF), among other common names. For example, in some configurations, in an adult patient, "high flow therapy" may refer to the delivery of gas to the patient at a flow rate of about 10 liters per minute (10 LPM) or greater, such as from about 10 LPM to about 100 LPM, or from about 15 LPM to about 95 LPM, or from about 20 LPM to about 90 LPM, or from about 25 LPM to about 85 LPM, or from about 30 LPM to about 80 LPM, or from about 35 LPM to about 75 LPM, or from about 40 LPM to about 70 LPM, or from about 45 LPM to about 65 LPM, or from about 50 LPM to about 60 LPM.In some configurations, in a neonatal, infant, or pediatric patient, "high flow therapy" may refer to the delivery of gas to the patient at a flow rate greater than 1 LPM, such as from about 1 LPM to about 25 LPM, or from about 2 LPM to about 25 LPM, or from about 2 LPM to about 5 LPM, or from about 5 LPM to about 25 LPM, or from about 5 LPM to about 10 LPM, or from about 10 LPM to about 25 LPM, or from about 10 LPM to about 20 LPM, or from about 10 LPM to 15 LPM, or from about 20 LPM to 25 LPM. A high flow therapy device in an adult, neonatal, infant, or pediatric patient may deliver gas to the patient at a flow rate of from about 1 LPM to about 100 LPM, or any of the subranges recited above.

[0369] High-flow therapy can be effective in meeting or exceeding a patient's inspiratory demand, increasing the patient's oxygenation, and / or reducing the work of breathing. Furthermore, high-flow therapy can create a flushing effect within the nasopharynx, such that the anatomical dead space of the upper airway is flushed with the high inlet gas stream. The flushing effect can create a reservoir of fresh gas available with every breath, while minimizing rebreathing of carbon dioxide, nitrogen, etc.

[0370] A patient interface for use with high-flow therapy may be a non-sealing interface to prevent barotrauma, which may include tissue damage to the lungs or other organs of the patient's respiratory system due to pressure differentials relative to the atmosphere. The patient interface may be a nasal cannula having a manifold and nasal prongs, and / or a face mask, and / or a nasal pillows mask, and / or a nasal mask, and / or a tracheostomy interface, or any other suitable type of patient interface.

[0371] Exemplary Low and / or Out of Water Detection Process Exemplary low-water and / or out-of-water detection processes are described with reference to FIGS. 3A-7. These detection processes may be implemented in any of the hardware configurations described above, a surgical air delivery system (as shown in FIG. 2D), or any other humidified respiratory support device configuration. As shown in FIG. 3A, in step 302 of an exemplary process 300 for detecting a low-water and / or out-of-water condition, a controller in the respiratory humidifier system can measure the heat capacity of the humidifier chamber. Water has a specific heat capacity of approximately 4,184 joules per kilogram per 1°C increase in temperature, which is greater than the specific heat capacity of the humidifier chamber material (not including the contents within the humidifier chamber). Therefore, the specific heat capacity of the humidifier chamber measured in step 302 decreases with a decrease in the amount of water because less energy is required to heat this reduced amount of water for each unit of temperature. Because the heat capacity of the humidifier chamber is lowest in the out-of-water case, the temperature change in the chamber is most rapid for a given change in power input. In comparison, the more water present in the humidifier chamber, the slower the temperature change for the same power input. This correlates with an increased specific heat capacity: the more water there is, the more heat energy is absorbed.

[0372] As described in more detail below, the controller may infer a value for the specific heat capacity (e.g., by determining a drainage score associated with the specific heat capacity value) without actually calculating the specific heat capacity value. The controller may also be able to calculate an actual value for the specific heat capacity of the humidifier chamber based on the humidifier chamber, water, heater plate, or other known variables necessary to calculate the specific heat capacity value. The controller may also be able to infer the actual value for the specific heat capacity from a determined value, such as a drainage score.

[0373] In decision step 304 of process 300, the controller can perform a water-out detection analysis by inferring the amount of water in the humidifier chamber based on the heat capacity of the humidifier chamber. The controller can determine whether the determined specific heat capacity value is less than a low water or water-out threshold. If the determined specific heat capacity value is less than the threshold, the controller can output a low water and / or water-out alarm in step 306, and the controller can return to step 302. If the determined specific heat capacity value is not less than the threshold, the controller can return to step 302.

[0374] FIG. 3B illustrates an exemplary process 310 for detecting low and / or out-of-water conditions. Process 310 can measure changes in temperature measurements by a temperature sensor on or near the heater plate. More specifically, process 310 can determine the specific heat capacity of the humidifier chamber by processing and analyzing signals of specific frequencies from the temperature sensor on or near the heater plate to detect low and / or out-of-water conditions. In step 312, the controller can apply a complementary signal to the heater plate power signal, such as by injection. In the disclosure herein, the complementary signal is also referred to as a characteristic energization signal. The complementary signal can be of a predetermined frequency different (e.g., higher or lower) than a conventional heater plate control power signal. In step 314, the controller can receive a feedback signal, obtained from data from a temperature sensor on or near the heater plate, after passing through a bandpass filter (see bandpass filter 426 in FIG. 4A). That is, the feedback signal is of the same predetermined frequency as the applied signal and represents a response to the complementary signal.

[0375] In step 316, the controller can measure the magnitude of the feedback signal component that correlates with the complementary signal, for example, by frequency-domain filtering. Magnitude is defined as the deviation from zero. At a given applied signal frequency, a humidifier chamber with a large amount of water can attenuate the feedback signal more (i.e., have lower gain) than a humidifier chamber with a small amount of water. As shown in FIG. 3C, periods of water-out conditions are indicated by the x-axis after or to the right of the black arrow. During water-out, the amplitude / deviation of the exemplary feedback signal is greater than before water-out (before or to the left of the black arrow). Thus, the magnitude and / or phase of the feedback signal may be inversely proportional to the specific heat capacity of the humidifier chamber. The inverse correlation between magnitude (and / or phase) and specific heat capacity is due to the fact that as the water runs out or the amount of water decreases, the specific heat capacity decreases, resulting in less absorption of the complementary signal. As the water runs out or the amount of water decreases, the temperature change increases. Thus, the thermistor in the heater plate detects a larger temperature change. Furthermore, if there is little or no water in the chamber, the time it takes for a change in heater plate power to manifest as a change in heater plate temperature may decrease. If there is sufficient water in the chamber, the temperature deviation response may be slower. As disclosed herein, the magnitude may be measured in a specific frequency band. Complementary signals of more than one frequency may also be used in process 310. If multiple frequencies are used, the controller may determine a weighted sum of the magnitudes at different frequencies as a ratio of the magnitude of the feedback signal, rather than the absolute magnitude. Complementary signals of any period and / or amplitude may be used. Preferably, the amplitude is small enough so that the complementary signal does not interfere with normal humidity control, including normal heater plate (HP) control.

[0376] Figure 3D shows an example heater plate response to the complementary signal in the time domain. As shown in Figure 3D, the response between when there is sufficient water in the chamber ("wet") 324 and when there is little or no water in the chamber ("dry") 322 may differ in magnitude and / or phase. Figure 3E shows the two responses in the frequency domain: when there is sufficient water in the chamber ("wet") 326 and when there is little or no water in the chamber ("dry") 328. As mentioned above, the difference in magnitude of the fundamental frequency of the two responses can allow for detection of an out-of-water condition.

[0377] The chart in FIG. 3E does not provide information regarding the phase difference between the two responses. The magnitude difference and the phase difference may be shown in a single graph. The controller may receive information regarding the magnitude and / or phase of the response to the complementary signal, which may or may not be a specific frequency band (e.g., the frequency of the complementary signal). The magnitude information may be extracted by any method disclosed elsewhere in this disclosure. Furthermore, the magnitude and / or phase information may be extracted by other methods, such as using a finite impulse response (FIR) filter, cross-correlation, performing homodyne detection or quadrature modulation, and / or a Fourier transform. For example, a process may be implemented to calculate the Fourier transform of a specific bin or frequency. The above-described method may convert the response to the complementary signal into data points in a two-dimensional space, which may be represented as polar or Cartesian coordinates (having real and imaginary values), as shown in FIGS. 3F-3H.

[0378] 3F-3H show exemplary representations of both magnitude and phase in two-dimensional space depicted as quadrants (0°-90°) of a signal space diagram, as well as different classification approaches for the out-of-water condition, e.g., based on magnitude alone (FIG. 3F), phase alone (FIG. 3G), and both magnitude and phase (FIG. 3H). The diagrams can show the harmonic content of the response to the complementary signal relative to the phase of the complementary signal. For example, the fundamental (also known as first) harmonic content is plotted. If other harmonic content is used, a classifier can use the other harmonic content alone or in combination with the fundamental content. As shown in FIGS. 3F-3H, the data points can generally be clustered into a "wet" (chamber with water) region 330 and a "dry" (chamber with little or no water) region 332. A classifier can be used to distinguish between these two regions, allowing a controller to detect whether an out-of-water condition exists.

[0379] As shown in Figure 3F, an out-of-water detection method based solely on the magnitude of the response to the complementary signal can determine a classification boundary 334. The classification boundary 334 can be a circular arc concentric to the signal space diagram, with all points on the arc representing the same magnitude at different phases. Any data point that falls on the side of the classification boundary 334 that is farther from the origin of the signal space diagram can indicate an out-of-water condition.

[0380] As shown in Figure 3G, an out-of-water detection method based solely on the phase of the response to the complementary signal can determine another classification boundary 336. The classification boundary 336 can be a line emanating from the origin of the signal space diagram, with all points on the line representing the same phase at different magnitudes. Any data point below the classification boundary 336 can indicate an out-of-water condition.

[0381] The outside of the classification boundary where a water-out condition exists can also be any two-dimensional shape that takes into account both magnitude and phase information. For example, the shape can be a circle, an eclipse, a zigzag line, a line that does not originate from the origin of the signal space diagram, an arc that is not concentric with the signal space diagram, or a free-form boundary. Figure 3H shows two exemplary two-dimensional shapes 338, 340 of a classification boundary that takes into account both magnitude and phase information. A water-out condition can be detected if a data point lies to the right of shape 338 or in an area outside the area enclosed by shape 340. Using both magnitude and phase information can improve the classification boundary because it allows data points to be further away from the boundary compared to classification boundaries 334, 336 based solely on magnitude or phase.

[0382] The location and / or shape of the classification boundary may be determined using any suitable method, for example, multivariate regression, machine learning (e.g., support vector machines), and / or other training models.

[0383] Returning to FIG. 3B, at decision step 318, the controller can perform a water-out detection analysis by inferring the amount of water in the humidifier chamber based on the magnitude of the temperature signal. The controller can determine whether the determined magnitude exceeds a low water and / or water-out threshold. At step 320, if the determined magnitude exceeds the threshold, the controller can output a low water and / or water-out alarm. If the determined magnitude does not exceed the threshold, the controller can return to step 312.

[0384] The sensing processes disclosed herein, such as applying (e.g., injecting), receiving, and / or measuring steps, can occur continuously, independent of whether the magnitude exceeds a threshold. Thus, the steps described with reference to Figures 3A and 3B continue to operate continuously, such that after outputting a low water and / or out of water alarm at steps 306 and 320, respectively, the processes of Figures 3A and 3B can return to the first step (step 302 of Figure 3A and step 312 of Figure 3B).

[0385] FIG. 4A shows a system diagram for implementing the processes 300 and 310 described above. As shown in FIG. 4A, the humidifier system 400 can be and / or incorporate any of the features of the systems 100, 200, 10, and 1 described above. For example, the humidifier system 400 can include a heater base unit 402 having a heater plate 420 that can contact a conductive base of the humidifier chamber 403 during use. The heater plate 420 can include one or more heating elements for heating the humidifier chamber 403. The heater base unit 402 can also include one or more heater plate temperature sensors (such as at least one thermistor), as described above.

[0386] A control unit for the humidifier system 400, which may be located within the housing of the heater base unit 402, generates a steady-state heater plate power signal P to control the delivery of humidification therapy. HP Due to inherent system response constraints, the heater plate control and its output power signal P HP is slow, with its spectral content extending from DC to approximately 0.005 Hz. This is shown in FIG. 4B, where the spectral energy due to the control response is clustered at low frequencies near the bottom of the spectrogram. The control unit may also include a waveform generator 424. The waveform generator 424 generates a complementary or characteristic power or energization signal ΔP WO is generated and used as the heater plate power signal P HP The complementary signal ΔP is superimposed on the WO may have a total amplitude of about 5 W to about 30 W, or about 10 W to about 25 W, or about 15 W to about 20 W, or about 16 W, or about 5 W to 15 W, or about 5 W to 10 W, or about 7 W to 10 W, or about 8 W. In one exemplary implementation, the total amplitude is about 5 W to about 30 W.

[0387] Complementary signal ΔP WOmay have a predetermined frequency (for example, about 0.005 Hz to about 0.025 Hz, or about 40 seconds to about 200 seconds, or about 50 seconds to about 150 seconds, or about 75 seconds to about 125 seconds, or about 100 seconds, or about 0.0055 Hz to about 0.015 Hz, or about 0.006 Hz to about 0.010 Hz, or about 0.00833 Hz, or about 120 seconds). WO The frequency or frequencies of the heater plate power signal P HP may be different from the frequency of the heater plate power signal P HP (or at least 1.5 times the frequency of the heater plate power signal PHP). WO is the composite heater plate power signal P HP To obtain the heater plate power signal P HP This is similar to frequency division multiplexing of the two signals. As described below, the heater plate power signal P HP and complementary signal ΔP WO A frequency domain guard band between , , and can facilitate separation / demultiplexing of these signals at a later stage.

[0388] FIG. 4B shows a complementary signal ΔP having a period of about 40 seconds to about 200 seconds, or about 80 seconds to about 120 seconds. WO The heater plate temperature signal T in the frequency domain as well as in the time domain shown on the spectrogram, with HP ' shows an exemplary waveform. In one exemplary implementation, the period is 120 seconds. The frequency band of approximately 1 / 120 Hz corresponds to the conventional heater plate control signal P HP The complementary signal ΔP added above WO As described in more detail below, this is the signal ΔT that is bandpass filtered and sent to detector 428 to determine if a low water and / or out of water condition exists. WO The approximately 2 / 120 Hz frequency band, which is weaker than the approximately 1 / 120 Hz frequency band, may produce a complementary signal ΔP WOThe frequency response from 0 Hz to approximately 0.005 Hz, which has higher intensity compared to the frequency band of approximately 1 / 120 Hz, represents the response of a conventional heater plate controller during start-up and when the water runs out.

[0389] Complementary signal ΔP WO can be any periodic waveform such as a triangle wave, square wave, sawtooth wave, or other. The waveform is similar to that of a conventional heater plate controller and its output P HP However, the summed power P HP Since ' cannot be negative, there is a limit to the negative amplitude of the waveform selected. WO may have an asymmetric waveform to increase (possibly maximize) the transmitted amplitude for a given negative amplitude and improve the signal-to-noise ratio. WO The waveform of the complementary signal ΔP can be easily generated at run time. WO The waveform may also have low harmonic content to avoid interference with the heater plate controller.

[0390] 4C shows example waveform candidates for the complementary signal: a simple triangle wave and a cubed triangle wave with the same negative amplitude after normalization to zero mean. The cubed triangle wave has a 3:1 ratio between positive and negative amplitudes, compared to the 1:1 ratio for a symmetric waveform such as a simple triangle wave.

[0391] Figure 4D shows the spectral content of two waveform candidates calculated by Fourier analysis. It can be seen that the cubed triangle wave emits nearly twice the energy at the fundamental frequency for the same negative amplitude, at the expense of higher energy in the upper harmonics. These harmonics may interfere with the heater plate controller. However, as shown in the Bode plot (frequency transfer plot) of heater plate temperature in Figure 4E, higher frequencies are highly attenuated, so the upper harmonics have little and / or negligible effect on the control unit's control of the heater plate temperature.

[0392] Continuing with reference to FIG. 4A, the controller generates a composite heater plate power signal P HP ' can be sent to the heater plate 420 of the respiratory humidifier system 400 to energize the heater plate 420. The controller receives the temperature sensor signal T HP ' can be received. HP ' is the heater plate power signal P HP and complementary signal ΔP WO FIG. 4F shows the composite signal P HP ' and the temperature sensor signal T HP 1 shows an example waveform of '.

[0393] With further reference to FIG. 4A, the temperature sensor signal T HP ' can be demultiplexed by filtering (e.g., by bandpass filter 426). The disturbance due to the complementary signal is filtered out, leaving the steady-state heater plate temperature signal T HP is generated and returned to the heater plate control 422 to maintain normal operation of the respiratory humidifier system 400. WO The feedback temperature signal ΔT WO (T through filter 426 HP The signal (which may be generated by bandpass filtering ') may be provided to detector 428. Detector 428 may implement any suitable water out-of-water detection algorithm.

[0394] Figure 4G shows the heater plate temperature signal T HP and the feedback temperature signal ΔT WO 1 shows an exemplary filter that is a second-order infinite impulse response (IIR) filter for separating the feedback signal ΔT WO bandpass filter to generate the steady-state heater plate temperature signal T HPThe filter may be a bandstop filter to generate . Different types of filters can be implemented to perform this filtering, such as a Finite Impulse Response (FIR) filter or a Cascaded Integrator-Comb (CIC) filter. The controller may also be capable of multi-rate processing, which does not require sampling every second to reduce the computational workload.

[0395] Exemplary Temperature Measurements with the Thermistors on the Heater Plate The heater plate temperature can be measured by one thermistor, the resistance of which is related to temperature. The heater plate temperature may be measured by two thermistors. The control unit can receive one input from each of the two thermistors.

[0396] Thermistors can measure temperature by using a voltage divider circuit to measure the change in voltage resulting from changes in the thermistor's resistance. The thermistor's resistance changes as the temperature changes. The thermistor's resistance correlates to a change in the thermistor's voltage. This thermistor voltage is sent to an analog-to-digital converter (ADC) input of a microcontroller, such as a microcontroller in a control unit. The control unit can convert the voltage reading to a temperature value using a computational model (such as a polynomial equation or other) based on the thermistor's datasheet. Calculating the temperature from the voltage reading can be more efficient than converting the voltage reading back to a resistance value and looking up the corresponding temperature value in a lookup table.

[0397] Exemplary Low and / or Out of Water Detection Algorithm An exemplary low water and / or out of water detection algorithm that may be implemented in the final step of the above-described processes 300, 310 will now be described with reference to FIG. 5A. The control unit may convert the magnitude and / or phase of the feedback signal into a numerical score. When the numerical score of an activation threshold for a low water and / or out of water condition is reached, the control unit may output a low water and / or out of water notification and / or activate a low water and / or out of water alarm by outputting a binary mask value of 1. When the threshold numerical score falls below a deactivation threshold, the control unit may deactivate the low water and / or out of water alarm by outputting a binary mask value of 0.

[0398] As shown in FIG. 5A, in step 502, the control unit can clip spikes in the temperature reading to eliminate false readings due to transient events. The threshold is set to be just outside the normal signal amplitude to reduce downstream effects of outliers while not affecting normal response. Fast transients and / or spikes can be caused by events such as filter initialization, filter ringing, physical disturbances, filling of the humidifier chamber with water, etc. Fast transients may have rich harmonic content (e.g., a Dirac delta impulse may have energy at all frequencies) and can cause sudden spikes in the numerical score and / or false low-water alarms. The Q value of the band filter can also be optimized to improve filter selectivity, reduce group delay, and / or reduce filter ringing effects. For example, a band filter with a low Q value can be selected to reduce ringing.

[0399] In step 504, the feedback temperature signal ΔT WO Upon receiving the feedback temperature signal ΔT WO The controller can measure the magnitude of the feedback temperature signal ΔT WOBy squaring the instantaneous value of and averaging this squared value using a downstream low-pass filter, a magnitude measurement similar to a root-mean-square (RMS) operation can be obtained. The controller may also be able to calculate the root-mean-square of the average values ​​to obtain the true RMS value. However, this may not be necessary, and the square-root step can be omitted, reducing the computational load on the control unit.

[0400] As shown in FIG. 5A, a low-pass filter (such as an IIR filter) can be applied in step 506 to average the instantaneous magnitude values ​​obtained in step 502.

[0401] In step 506, the control unit can also employ disturbance suppression strategies to prevent the filter from reacting to fast transient spikes that could cause false water shortage alarms. Disturbance suppression strategies can include selectively slowing down filter updates when the heater plate is not at the setpoint temperature. The selective slowing down is achieved by selectively slowing down the control deviation (ε HP ) is multiplied by the filter coefficient, and ε HP This can be achieved by outputting a value close to the previous value when .

[0402] In step 508, the control unit can apply a threshold discriminator (such as a simple threshold discriminator with hysteresis) that can determine whether the numerical score obtained after step 506 is above or below a threshold boundary. The threshold boundary can be equal to 0.17 degrees RMS (2 d.p.) or any other suitable boundary. If the numerical score obtained after step 506 exceeds the threshold boundary, the control unit can output a low water and / or out-of-water notification and / or issue an alarm (such as a visual and / or audio cue or other). Figure 5B shows an exemplary out-of-water score when an out-of-water condition occurs. As shown in Figure 5B, the control can activate an out-of-water alarm when the out-of-water score exceeds approximately 10.

[0403] Exemplary Further Temperature Signal Magnification In step 502, the feedback temperature signal ΔT WO The magnitude of ΔT may also be determined using principles similar to a direct conversion receiver (homodyne). Specifically, matched filtering is performed on the feedback signal ΔT WO and complementary signal ΔP WO This can be implemented by convolving the temperature signal ΔT with the feedback temperature signal ΔT, which includes both magnitude and phase information. This allows all harmonics to be processed simultaneously and provides improved discrimination. Signals with multiple frequencies can be processed simultaneously. The control unit may also use the feedback temperature signal ΔT to reduce the computational load on the control unit. WO The magnitude of may be calculated by matched filtering without determining the phase.

[0404] Feedback temperature signal ΔT WO The magnitude of the feedback temperature signal ΔT may also be determined using a leaky peak detector implementation similar to the electronic circuit shown in FIG. WO If the amplitude of the feedback temperature signal ΔT is high, the capacitor will charge until it coincides with the peak. WO When the amplitude of the feedback temperature signal ΔT is low, the capacitor discharges slowly. The resistance value of the resistor and the capacitance value of the capacitor can be selected to control the time it takes for the capacitor to discharge and react to a drop in amplitude. The maximum charging amplitude of the capacitor is determined by the feedback temperature signal ΔT WO Indicates the maximum magnitude of.

[0405] Exemplary Alarm Reset After issuing a low and / or out of water alarm, the control unit may reset the alarm in a different manner than based on the numerical out of water score, i.e., by waiting for a binary mask output of 0 from the low and / or out of water detection algorithm. The low pass filter in step 506 is selected to be slow to avoid false triggers due to transient conditions, which may cause the out of water score to remain high for a period of time after refilling the water. Therefore, resetting the out of water alarm using the out of water score may be slow (e.g., temperature signal decay may take several minutes).

[0406] The control unit monitors the temperature drop of the heater plate below its set point (e.g., T HP <(T HP_SETPOINT A water shortage alarm may be reset if the water temperature drops below -3°C. This reset condition may allow the control unit approximately 30 seconds of detection time when the humidifier chamber is refilled with cold water. Under normal operation, the heater plate temperature control maintains the heater plate near the setpoint. Therefore, a drop in heater plate temperature can be used to detect a cold water refill, since no other refill would cause the heater plate temperature to drop so quickly. This method may have a different detection time if hotter water is refilled into the humidifier chamber. Values ​​other than 3°C may also be used as the reset condition threshold. This reset condition may be more effective than waiting for the signal to decay, such that the control unit returns to a binary mask output of 0.

[0407] The low and / or out of water detection systems and methods disclosed herein may be advantageous over out of water detection based on thermal conductivity determinations that typically rely on other temperature sensor readings, gas flow rates, etc. As described below, the present low and / or out of water detection disclosure provides faster detection of low and / or out of water conditions, more accurate and / or reliable detection of low and / or out of water conditions, and requires fewer sensor components.

[0408] The low and / or out-of-water detection systems and methods disclosed herein can be independent of flow rate changes. Flow rate changes may change the DC (i.e., steady-state) operating point of the heater plate transfer function (e.g., more power is required to maintain temperature at increased flow rates, resulting in a decrease in DC gain (°C / W)), but do not affect the high-frequency components when a complementary signal is present. As shown in FIG. 7, the change in heater plate temperature gain is negligible at the higher frequencies where the low and / or out-of-water detection algorithm is applied. Respiratory humidifier systems may also be more accurate in detecting out-of-water conditions in cases of low-flow noninvasive therapy (e.g., pediatric noninvasive therapy flow rates below about 10 L / min) or very low-flow invasive therapy (e.g., neonatal invasive therapy flow rates below about 5 L / min).

[0409] The low and / or out-of-water detection system and method disclosed herein can also be independent of the heater plate control. The out-of-water detection process does not need to replace the normal operation of the system. Rather than detecting low and / or out-of-water conditions across the entire transfer function, the characteristics of the humidifier chamber at specific frequencies are used to reduce exposure to errors and improve the resilience of the detection method. The complementary signal can be multiplexed and then demultiplexed from the heater plate control signal via frequency division. This (de)multiplexing process can be transparent and cannot interfere with the heater plate control used for humidity delivery. Therefore, unlike some detection processes that require replacing the normal operation of the system, the low and / or out-of-water detection process disclosed herein can run continuously. The out-of-water detection process also does not involve complex state transitions and / or trigger conditions.

[0410] Because the out-of-water detection process can continuously measure the specific heat capacity of the humidifier chamber and output a numerical score, the control unit can also compare the numerical out-of-water score to various threshold boundaries that can also enable the control unit to optionally provide potential warnings, such as a "low water" warning, before an actual out-of-water condition occurs.

[0411] The water out detection process disclosed herein may also enable the control unit to observe characteristic responses so that it can distinguish between different types of humidifier chambers and / or detect when a chamber is not engaged with the heater-based unit.

[0412] Overview of an Exemplary Low and / or Out of Water Detection System As described herein, certain exemplary methods for detecting low and / or out-of-water conditions in the humidifier chamber are based in part on heater plate temperature measurements. However, the presence of other components in the heater plate assembly may affect the true heater plate temperature for a given power provided to the heating elements of the heater plate assembly. HPThis can result in energy losses and / or thermal inefficiencies such that the heater plate temperature (heater plate temperature) does not correspond. In some alternative configurations, the heater plate temperature may be used as a proxy for or a proxy for water temperature. This reduces the accuracy of the low water and / or out-of-water condition detection technique. Furthermore, additional losses due to poor thermal contact between various components of the heater plate assembly can contribute to inaccuracies in low water and / or out-of-water condition detection. FIGS. 8A and 8B schematically illustrate example system or circuit models 800, 801 to aid in understanding how to reduce parasitic capacitance elements and / or resistance in low water and / or out-of-water detection. The systems 800, 801 can also be configured to enhance or maximize water capacitance detection. The systems 800, 801 can be configured to improve thermal coupling of the heater plate components, including the heating element and the upper and lower heating plates, and to improve contact between the humidifier chamber and the heater plate.

[0413] The system 800, 801 can measure the gain of the transfer function at a particular frequency as seen at the heater plate temperature measurement point T_HP, which can be correlated to the presence or absence of water (or specific heat capacity, if desired).

[0414] As seen in systems 800 and 801, all components at or downstream of the heater plate temperature measurement point can contribute to gain. An effective electrical model of the entire system provides an improved understanding of the overall gain of the system, including parasitic capacitances and resistances. The capacitance C water In addition to the capacitance C heaterPlate , C chamber , as well as resistance θ2 (heater plate-chamber contact) and resistance θ3 (chamber-water contact). evaporationchanges the DC operating point but does not significantly affect the transfer function at high frequencies. Furthermore, in system 801, all components on either side of the heater plate temperature measurement point can affect the temperature value observed at the heater plate. Each stage of system 801 (e.g., upper heating plate, humidifier chamber, etc.) can be interpreted as a resistor-capacitor (RC) stage (see FIG. 8C) that attenuates the temperature rise signal as heat enters the water in the chamber. This results in a steady-state temperature difference (DC attenuation) at the different measurement points, as well as low-pass filtering and / or additional attenuation at high frequencies.

[0415] These extra parasitic terms (C heaterPlate , C chamber , θ2, and θ3, etc.) and C water It may be desirable to measure only the contribution of C. For example, if the C term is water (e.g., C for a chamber with a thick metal base) chamber , or C heaterPlate , C topPlate and / or C. botPlate is large), for example, there is a difference of 10-15 instead of 0-5, so C water Similarly, if the thermal resistance θ term (e.g., θ2 or θ3) is large, C water becomes more decoupled from the heater plate temperature measurement. water Changes due to may have little effect on the measured gain. As the parasitic terms increase, the accuracy of the water out detection method decreases because the applied characteristic energization signal is lost in the parasitic terms. The loss of signal, or the reduction in the characteristic energization signal received by the water, reduces the accuracy and effectiveness of the water out detection method. Figure 8B shows a more detailed model of the system. Figure 8B shows that the heater plate can be modeled as a heater element as well as an upper heating plate and a lower plate. Each element in the system is modeled as an RC circuit. As can be seen in Figure 8B, the lower plate is modeled as a resistor and capacitance. The heating element and upper heating plate are modeled similarly.

[0416] As shown in Figure 8C, the interaction between these resistive and capacitive terms in the systems of Figures 8A and 8B forms an RC filter, attenuating high-frequency signals by introducing a pole into each RC stage. The bandwidth of a first-order RC filter is related to its time constant, τ = RC. This represents the time it takes for the output to reach 63% of the input, and is also the reciprocal of its bandwidth (radians / second). At high frequencies, filters with small time constants have minimal effect, while larger time constants can have a greater attenuation effect. A low τ value is desirable for the parasitic terms to allow for more direct transfer of the high-frequency energy of the applied waveform to the water in the humidifier chamber during the low-water and / or out-of-water detection process. A larger time constant can cause more attenuation of the applied waveform, resulting in a reduction in the feedback amplitude of the applied waveform.

[0417] The value of the R term and / or the C term can be reduced to reduce τ. A reduction in the value of C (such as by using less material in the top and / or bottom plates) botPlate and C topPlate θ1a, θ1b, and θ1c. Reductions in the value of R (i.e., θ1a, θ1b, and θ1c) can be achieved by improving thermal energy transfer. As described in more detail below, compliant electrical insulator material can be added to improve thermal coupling between the heating element and the upper and lower heating plates. Electrical insulators are thermal conductors. The use of compliant insulators reduces the R term by improving thermal coupling between the elements of the system, particularly the components of the heater plate assembly. Reducing the R value of the heater plate assembly allows for smaller waveforms of the characteristic energization signals for low water and / or out-of-water detection (thus reducing the likelihood of clipping at lower power levels as shown in FIG. 8D) required to achieve the same return signal amplitude.

[0418] FIG. 8D illustrates exemplary clipping of the application characteristic energization signal. While FIG. 8D illustrates a sine wave, the principles of reducing clipping may equally apply to other waveforms, such as a cubed triangular waveform. Negative power is not possible in the heater plates disclosed herein. Therefore, negative power values ​​are clipped. In some cases, large positive powers may be clipped if power supply limits are reached. Humidifiers of the present disclosure generally operate off mains power or may include battery power. The operating power range may not result in clipping of positive power values. To reduce the range of clipping, the negative amplitude |min(P wave )| is usually used |P ss The characteristic energization signal (e.g., a larger injected signal) amplitude can be maintained below the minimum steady-state power at a given signal amplitude. For example, lower steady-state power may occur during lower flow conditions. However, on the other hand, a larger characteristic energization signal (e.g., a larger injected signal) amplitude can improve the signal-to-noise ratio and improve the sensing and / or measurement of the feedback signal. A larger applied signal may be necessary to compensate for losses and obtain the feedback signal. Further increasing the feedback signal amplitude or improving the signal-to-noise ratio can assist in water starvation detection. A larger applied signal may also be necessary due to heat losses through various components of the heater plate. The electrical insulator material can enhance the thermal response of the characteristic energization signal at a given signal amplitude. In other words, the electrical insulator material allows the same magnitude of thermal response to be achieved with a smaller characteristic energization signal amplitude, thereby reducing the likelihood of clipping of the applied signal.

[0419] FIG. 9 illustrates an exemplary heater plate assembly 900 as described in International Publication No. WO2015038014. As shown in FIG. 9A, the heater plate assembly 900 may include, among other components, an upper heating plate 910, a lower plate 920, a heating element subassembly 930, and a single insulating sheet 940 between the heating element subassembly 930 and the upper heating plate 910. The insulating sheet 940 may be a polyetheretherketone (PEEK) material or a flexible and compliant thermal interface material as disclosed herein. Compliant, in this disclosure, may refer to the ability of a material to soften, compress, and / or conform to the shape of surfaces, allowing the material to displace air gaps between the surfaces sandwiching the material (see, for example, thermal interface material 1338 in FIGS. 13B and 13D). The insulating sheet 940 may also be elastic, allowing the insulating sheet 940 to accommodate shear forces and movements of the upper heating plate and / or lower plate.

[0420] FIG. 9A illustrates another exemplary heater plate assembly 900 that utilizes at least a layer of thermal interface material, such as the thermal interface material used in electrical insulation sheet 940 or sheet 941, to enhance heat transfer. FIGS. 9B-9D illustrate the heater plate assembly 900 of FIG. 9A as assembled (wires for connecting to a power source are not shown). The use of thermal interface material can improve coupling from the heater plate to the humidifier chamber and reduce the amplitude of the waveform of the applied characteristic energization signal. This further enables the low water and / or out-of-water detection methods disclosed herein to be implemented at lower power levels, such as during low flow rates, low humidity, and / or when the chamber is absent. Furthermore, the use of thermal interface material improves thermal coupling between the heater plate components, allowing most (or all) of the heat generated by the heating element subassembly to be more efficiently transferred to the upper heating plate and the water in the humidifier chamber.

[0421] 9A , heater plate assembly 900 may include, among other things, an upper heating plate 910, a lower plate 920, a heating element subassembly 930, an insulating sheet 940, and a sheet 941. Insulating sheet 940 may be an electrical insulator to prevent short circuits and / or the transmission of electrical current to upper heating plate 910 and / or lower plate 920, which could create an electric shock risk. Sheet 941 may or may not be electrically insulating (i.e., sheet 941 may or may not be conductive). Insulating sheet 940 or sheet 941 may include one sheet of PEEK and one sheet of compliant thermal interface material. In one configuration, both insulating sheet 940 and sheet 941 can be soft, compliant thermal interface materials that can be bolted to the heater plate assembly 900 and thus can move laterally, or preferably in all directions, to improve thermal coupling (i.e., thermal contact between the heating element and the components of the heater plate assembly, including the upper and lower plates). The upper and lower plates 910 and 920 can be rigid. The upper heating plate 910 can be at least partially exposed to ambient air when not in use. For example, the upper surface of the upper heating plate 910 can be at least partially exposed to ambient air when the humidifier chamber is not placed on the heater base. When the humidifier chamber is placed on the heater base, the upper surface of the upper heating plate 910 can contact the bottom surface (i.e., base) of the humidifier chamber. The upper heating plate 910 can be made of a thermally conductive material. The bottom surface of the humidifier chamber can also include a thermally conductive material. The upper heater plate 910 and the lower plate 920 may comprise a metallic material such as aluminum. Further details of exemplary components of the heater plate assembly are described in International Publication No. WO2015038014, the entire contents of which are incorporated herein by reference.

[0422] FIG. 9E illustrates an exemplary heating element subassembly 930. The heating element subassembly 930 can include one or more electrical insulating layers, sandwiching a heating element between the one or more electrical insulating layers. The heating element can include one or more heating filaments wound around a non-conductive core. As shown in FIG. 9E, the heating element subassembly 930 can include wires 936 for connecting the heating element to a power source. The heating element subassembly 930 can also include a first electrical insulating layer 932 and a second electrical insulating layer 934. A physical plate that is itself a heating element could completely eliminate the terms θ1a-θ1b (see FIG. 8B). However, because the heating element is powered by a utility power source, the electrical insulating layers can improve safety. Each of the multiple insulating layers 932, 934 can provide electrical insulation and thermal conduction. The multiple insulating layers 932, 934 may be made from mica sheets or other sheet electrical insulators such as silicone, polyetheretherketone (PEEK), or polyimide (e.g., Kapton, a registered trademark of EI du Pont de Nemours and Co.). The insulating layers 932, 934 may be glued or otherwise fastened to the heating element subassembly 930 and cannot move relative to the other components of the heater plate assembly 900. Additional insulating layers may be taped or otherwise fastened. The insulating layers 932, 934 may be inflexible or rigid. The insulating layers 932, 934 may have the same thickness or, alternatively, may be of different thicknesses, with one layer being thicker than the other. For example, one or more of the insulating layers may be greater than about 0.4 mm thick or less than about 0.4 mm thick. A third electrical insulator layer (not shown in FIG. 9E) may be included in the heating element subassembly 930. For example, the third layer can be located adjacent to the second layer 934 or adjacent to the first layer 932 .

[0423] In some configurations, the heating element subassembly 930 has a mica sheet on both sides of the subassembly 930. The mica sheet and the insulating sheet 940 or sheet 941 can provide double electrical insulation between the heating element and the upper heating plate 920.

[0424] Insulating sheet 940 or sheet 941 can be compliant or flexible (e.g., without limitation, having a Shore 00 hardness value of about 50 to about 100, or about 70 to about 90, or in one example, about 80). Insulating sheet 940 or sheet 941 can include a silicone-based, glass-reinforced thermal interface material having a compliant material with a smooth surface. Insulating sheet 940 can be non-stick on both sides of the sheet. Insulating sheet 940 and sheet 941 can be made of the same material or different materials.

[0425] Examples of insulating sheet 940 or sheet 941 may include, but are not limited to, Sil-Pad A1200, Sil-Pad 900S, Sil-Pad A2000, or Gap Pad VO manufactured by Bergquist, or Tgon 805-A0 (no adhesive) or Tgon 805-A1 (adhesive on one side) manufactured by Laird Technologies.

[0426] The insulating sheet 940 or sheet 941 may include an adhesive or may be adhesive-free. The thermal interface material may comply with IEC 60601-1 standards, for example, but not limited to, having a minimum breakdown voltage of at least 4 kV AC, or at least 5 kV AC, or at least 6 kV AC. The insulating sheet 940 or sheet 941 may be, for example, about 0.002" (0.05 mm) to about 0.04" (1.02 mm), or about 0.002" (0.05 mm), about 0.003" (0.08 mm), about 0.005" (0.13 mm), about 0.006" (0.15 mm), about 0.009" (0.23 mm), about 0.012" (0.31 mm), about 0.015" (0.38 mm), or about 0.016" (0.38 mm). The insulating sheet 940 or sheet 941 may have a thickness of, but is not limited to, about 0.016" (0.41 mm), about 0.018" (0.46 mm), about 0.02" (0.51 mm), about 0.025" (0.64 mm), about 0.03" (0.76 mm), or about 0.04" (1.02 mm). The insulating sheet 940 or sheet 941 may provide electrical insulation and may also provide insulation for the heating element 930. The insulating sheet 940 or sheet 941 can also improve thermal conduction between the heating element subassembly 930 and the upper heating plate (e.g., having a thermal conductivity of about 1.8 W / (mK)). The compliant insulating sheet 940 can improve thermal conductivity by conforming to the shape between the heating element 930 and the upper heating plate 910 and better thermally coupling the heating element 930 to the upper heating plate 910. The insulating sheet 940 or sheet 941 can also slide or translate against the inflexible or rigid insulating layer 934 to fill any gaps between the heating element subassembly 930 and the upper heating plate 910. The improved thermal coupling between the heating element subassembly 930 and the upper heating plate 910 can improve water drainage.

[0427] Further details of an exemplary heater plate assembly with improved thermal coupling are described with reference to FIGS. 10-19F. FIG. 10 illustrates a configuration without a thermal interface material. FIG. 10 illustrates a heater plate stack configuration 1000 with double insulation. Double insulation refers to two separate, discrete layers of insulating material between the heating element and each plate. This insulation is electrical insulation. In FIG. 10, the first double electrical insulation feature is one mica layer 1036 and a PEEK layer 1038 between the heating element 1035 and the upper heating plate 1010. The second double electrical insulation feature is two mica layers 1032, 1034 between the heating element 1035 and the lower plate 1020. Two separate layers of insulating material can provide redundancy; that is, if one fails, there is a second layer of insulating material. In heater plate assemblies with thermal interface material, the first dual electrical insulation feature may be a single mica layer and thermal interface material between the heating element and the upper heating plate. There are several different permutations and combinations of insulator sheets that can be arranged to achieve dual electrical insulation. In some configurations, there are more than two insulator sheets. The upper heating plate 1010 may include a recess to accommodate the heating element 1035 sandwiched between a first insulating layer 1032 and a second insulating layer 1034 on the side facing the lower plate 1020 and a third insulating layer 1036 and a fourth insulating layer 1038 on the side facing the upper heating plate 1010. The first layer 1032, the second layer 1034, and the third layer 1036 may include mica sheets. The fourth layer 1038 may include a flexible / compliant thermal interface material. In an alternative configuration, the fourth layer 1038 may include a PEEK sheet. A compliant thermal interface material is preferred because it can move and conform to the shape of the upper and lower plates and can compress to fill air gaps between the various components between which the thermal interface material is disposed, improving thermal contact. The lower plate 1020 can have a generally uniform thickness (e.g., have a generally disc shape) and can be disposed adjacent to the first insulating layer 1032. The outer edge of the lower plate 1020 can contact the upper heating plate 1010.

[0428] The heater plate assembly may have one compliant thermal interface material layer. This layer may be located between the heating element and the upper heating plate. The compliant thermal interface material layer may have a thickness sufficient to provide the necessary electrical insulation. Alternatively, the compliant thermal interface material layer may be used with an additional electrical insulation layer as described elsewhere. The heater plate assembly may also have two compliant thermal interface material layers.

[0429] FIG. 11 illustrates an exemplary heater plate stacking configuration 1100 that improves thermal coupling of heater plate components. This improved thermal coupling is achieved while also providing necessary electrical insulation. The stacking configuration provides a dual electrical insulation mechanism to electrically insulate each plate from the heating element to prevent shock. The upper heating plate 1110 may include a recess for receiving the heating element 1135 sandwiched between first and second insulating layers 1132, 1134 on the side facing the lower plate 1120 and third and fourth insulating layers 1136, 1138 on the side facing the upper heating plate 1110. The first, second, and third layers 1132, 1134, and 1136 may include mica sheets. The fourth layer 1138 may include a thermal interface material, which may be the material of sheet 940 or sheet 941 described above. 12A, insulating layer A (which may be fourth layer 1138 in FIG. 11) is located on the underside of the upper heating plate 1210 and is configured to contact the heating element subassembly. The fourth layer 1138 of thermal interface material, insulating layer A, can improve contact between the upper heating plate and the heating element subassembly.

[0430] As shown in FIG. 11 , a separate thermal interface material layer 1139 may be located at the interface between the upper heating plate 1110 and the lower plate 1120. The two thermal interface material layers 1138, 1139 may be the insulating sheet 940 or sheet 941 of FIG. 9A . The separate layer 1139 may be, but need not be, electrically insulating (i.e., it may be conductive). This separate layer 1139 is also illustrated in FIG. 12A as insulating layer B. Layer B may be located on a raised surface above the lower surface of the upper heating plate 1210. Layer 1139, i.e., layer B, may improve surface area contact between the upper heating plate and the lower plate. The second layer 1139 may also include cutouts or openings for receiving heating elements. The second layer 1139 may be made of the same material as the first layer 1138. The layers 1138, 1139 have the shape of the insulating sheet 940 or sheet 941 of FIG. 9A . The second layer 1139 is sandwiched between the upper heating plate 1110 and the lower plate 1120. The layer 1139 is sandwiched between the upper heating plate 1110 and the lower plate 1120 when the heater plate assembly 1100 is bolted together. Alternatively, the layer 1139 may be glued onto the underside of the upper heating plate 1110. The layer 1139 has openings therein to accommodate thermistor wells and bolt openings, such as thermistor well 1211 and bolt openings 1219 shown in FIG. 12B. FIGS. 12B-12C, 12F, and 12J show the underside of the upper heating plate 1210 without the insulating layer. The dashed line 1213 indicates the perimeter of the lower plate 1220, which is configured to contact the upper heating plate 1210, as shown in FIGS. 12D and 12E. The underside of the upper heating plate 1210 further includes a recess 1217 for receiving the heating element subassembly. Figures 12D and 12E show the underside of the lower plate 1220, which is configured to be received by the upper heating plate 1210. Dashed line 1223 indicates the perimeter of the heating element subassembly, such as a mica insulating sheet on one side of the heating element subassembly, which is configured to contact the lower plate 1220.The area between the edge of the lower plate 1220 and dashed line 1223 indicates the contact area between the upper heating plate 1210 and the lower plate 1220. Figures 12L and 12M show the underside of the upper heating plate 1210 without the insulating layer. Dashed line 1214 indicates the outer periphery of the lower plate 1221, which is configured to contact the upper heating plate 1210, as shown in Figures 12N-12R. Compared to the lower plate 1220, the lower plate 1221 includes a larger cutout area to improve thermal isolation between the thermistor well 1211 and the lower plate 1221. The area between the edge of the lower plate 1221 and dashed line 1223 on the lower plate 1221 indicates the contact area between the upper heating plate 1210 and the lower plate 1223. As mentioned above, insulating sheets referred to herein are electrical insulators that provide electrical insulation. These insulators, such as thermal interface materials, are thermal conductors rather than thermal insulators.

[0431] 13A-13D illustrate, at a microscopic level, the improved thermal contact achieved through the use of thermal interface materials. As shown in FIG. 13A, the rough surfaces of the upper heating plate and rigid insulating layers, such as the PEEK layer 1332 and mica layer of the heating element subassembly 1330, can lead to poor thermal conduction due to air pockets or gaps trapped between the upper heating plate and the rigid insulating layer. Similarly, as shown in FIG. 13C, the rough surfaces of the upper heating plate 1310 and lower plate 1320 can also lead to less-than-optimal heat transfer due to air pockets or gaps trapped between the rigid upper heating plate 1310 and the rigid lower plate 1320. As shown in FIGS. 13B and 13D, a compliant thermal interface material layer 1338, such as the insulating sheet 940 or sheet 941 described above, can displace the air pockets or gaps and improve the available surface area contact.

[0432] As shown in Figure 13B, a compliant thermal interface material layer 1338 can replace the rigid PEEK layer 1332 of Figure 13A to allow for better surface area contact between the heating element subassembly 1330 and the upper heating plate 1310. This compliant thermal interface material layer 1338 can lower θ1a in the equivalent circuit model or system 801 of Figure 8B.

[0433] As shown in Figure 13D, a compliant thermal interface material layer 1338 can be added between the upper heating plate 1310 and the lower plate 1320 to increase the surface area contact between the upper heating plate 1310 and the lower plate 1320. This compliant thermal interface material layer 1338 can lower θlc in the equivalent circuit model or system 801 of Figure 8B. Figure 13D shows the thermal contact, or thermal coupling, between the upper heating plate and the lower plate provided by sheet 1139 (layer B). Figure 13B shows the thermal coupling between the heating element assembly and the upper heating plate provided by sheet 1138 (layer A).

[0434] As seen in the equivalent circuit model or system 801 of FIG. 8B, lowering θ1a and / or θ1c can reduce the inherent filtering effect within the heater plate assembly. As a result, the applied waveform amplitude or power Pwave can be reduced to achieve the same target magnitude at T_HP. For purposes of low water detection and / or out-of-water detection, it may also be beneficial to lower θ1b by introducing thermal interface material along the entire surface of the lower plate, not just in the contact area between the lower plate and the upper heater plate.

[0435] FIG. 14 shows another exemplary heater plate stacking configuration 1400 that reduces material costs without compromising thermal coupling. The upper heating plate 1410 may include a recess to receive the lower plate 1420. The lower plate 1420 may include a recess to receive the heating element 1435 sandwiched between a first insulating layer 1432 and a second insulating layer 1434 on the side facing the lower plate 1420 and a third insulating layer 1436 and a fourth insulating layer 1438 (forming a heating element subassembly) on the side facing the upper heating plate 1410. The first layer 1432, the second layer 1434, and the third layer 1436 may include mica sheets. The fourth layer 1438 may include a thermal interface material, which may be the material of the insulating sheet 940 or sheet 941 described above. The fourth layer 1438 in FIG. 14 may be located over substantially the entire lower surface of the upper heating plate 1210 and may be configured to contact the lower plate 1420 and the third insulating layer 1436. A fourth layer 1438 of thermal interface material can improve contact between the upper heating plate 1410 and the lower plate 1420, and between the upper heating plate 1410 and the heating element subassembly.

[0436] As shown in FIG. 14 , a separate thermal interface material layer 1439 can be located at the interface between the underside of the lower plate 1420 and the first insulating layer 1432. This separate layer 1439 can improve the surface area contact between the lower plate 1420 and the heating element subassembly. In this alternative configuration as shown in FIG. 14 , layer 1439 thermally couples the heating element 1435 to the lower plate 1420, which is thermally coupled to the upper heating plate 1410 by layer 1438. This improves thermal conduction from the heating element 1435 to the upper heating plate 1410. Furthermore, heat to the lower plate 1420 is conducted to the upper heating plate through layer 1438. This can improve the temperature reading of the thermistor. This improved thermal coupling can also improve water shortage detection.

[0437] FIG. 15 shows a heater plate stack configuration 1500 that is substantially the same as configuration 1400 of FIG. 14 , except that configuration 1500 may not include a separate thermal interface material layer between the lower plate 1520 and the first insulating layer 1532. Similar features in FIGS. 14 and 15 share the same last two digits and are not repeated for simplicity. The fourth layer 1538 of thermal interface material need not be split into two parts, such as layers A and B in FIG. 12A . That is, a single thermal interface material layer can be used to improve thermal contact between the upper heating plate 1510 and the lower plate 1520, and between the upper heating plate 1510 and the heating element subassembly. This can improve the manufacturing process by reducing assembly time. The edges of the lower plate 1520 can be extruded or raised to create recesses to receive the heating element subassemblies. The recess can contain a heating element subassembly and be in contact with the thermal interface material 1538, or can thermally couple the thermal interface material 1538 to the upper heating plate 1510 and redirect thermal energy back to the upper heating plate 1510. Referring to Figure 8B, placement of the fourth layer 1538 of thermal interface material can lower θlc.

[0438] As shown in FIGS. 16A and 16B , the resistive heating element 1635 can be designed so that the heating filament 1637 is primarily wrapped around one side of the non-conductive core 1633 of the element 1635 (such as the side facing the upper heating plate). The filament 1637 can loop around the protrusion 1631 of the core 1633 so that the heating filament is primarily on one side of the non-conductive core. This wrapping configuration allows for heat conduction to be biased in one direction in the z-axis (see FIG. 14 ). The resistive heating element 1635 can be implemented in any of the heater plate stack configurations disclosed herein. Alternative configurations of the resistive heating filament configuration or a printed circuit board (PCB) with heating tracks on the heating element, such as copper etched tracks, can be used.

[0439] 17A-17E and 18A-18F show an exemplary upper heating plate 1710 and lower plate 1820 that may be used to implement the heater plate stack configuration 1500 of FIG. 15. In FIG. 17A, the shaded area 1711 indicates the die-cut shape of the thermal interface material, which may be the fourth layer 1538 of FIG. 15. In FIGS. 18A, 18E, and 18F, the shaded area 1821 indicates the edge region of the lower plate 1820 that is raised to contain heating element subassemblies, such as heating elements and other insulating layers, disclosed herein, while still allowing contact with the thermal interface material (such as the fourth layer 1538 of FIG. 15). FIGS. 19A-19E show another exemplary lower plate 1920.

[0440] Different thermal interface materials can be used on both sides of the heating element. The thermal interface material can be selected so that the heat vector from the heating element is substantially directed toward the upper heating plate. All or a combination of the mica insulating layers can be replaced with a thermal interface material. For example, at least one of the mica insulating layers between the lower plate and the upper heating plate can be replaced as shown in Figures 11, 14, and 16. The thermal interface material can optionally be positioned directly adjacent to the resistive heating track or filament of the heating element (i.e., without a rigid insulating layer between them). For safety reasons, because the thermal interface material can be rated for lower temperatures than the mica sheet, the thermal interface material also need not be positioned directly adjacent to the resistive heating track of the heating element (i.e., with at least one layer of rigid insulating layer, such as a mica sheet, between them). The entire heater plate assembly can be bolted together (e.g., without adhesive). Elements that are bolted together allow for easier removal or replacement of damaged elements. The bolted elements also allow the compliant insulator sheets (thermal interface material layers) to move relative to the other elements to accommodate gaps and eliminate air gaps. This improves the thermal coupling between the heating element, the lower plate, and the upper heating plate. The thermal coupling ensures that the majority of the heat from the heating element is transferred more efficiently to the upper heating plate, where it is detected by the thermistor. This also improves the accuracy of the water shortage detection method.

[0441] An additional layer of thermal interface material can also be added to the heater plate stack configurations disclosed herein. For example, a thermal interface material may be placed between the bottom plate and the mica insulation layer to reduce air pockets that may form in that area, as shown in Figure 14. Assembly of this additional layer can be part of the heating element assembly process or can be a separate step.

[0442] Systems 800, 801, 802 also illustrate that temperature measurements taken at locations and / or in ways other than the heater plate temperature sensor can be used for low water and / or out-of-water detection. For example, water temperature can be measured directly to eliminate the influence of the other factors mentioned above. Also, for example, temperature T heaterPlate and temperature T chamber Between or temperature T topPlate and temperature T chamber It is possible to cancel the effects of these parasitic terms by taking a differential measurement of the difference between the temperature and the temperature of the heater plate. For example, it is possible to have two thermistors on the heater plate, one closer to the element than the other. This two-thermistor configuration can improve the water shortage detection process by canceling out the parasitic terms.

[0443] The systems described herein may also include features configured to isolate sensors, such as the heater plate temperature sensors disclosed herein, from external thermal contributions. As described above, the heater plate temperature sensor may measure the upper heater plate temperature, which may be fed into a low water and / or out-of-water detection algorithm, during which a higher frequency complementary signal is applied to the heater plate control signal waveform. The complementary signal and the reflected response signal may be more sensitive to and / or attenuated by noise in the temperature measurement. To make the detection algorithm more reliable, for a given power provided to the heating elements of the heater plate assembly, the measured temperature T HP It would be beneficial if (Heater Plate Temperature) corresponded better to the true heater plate temperature.

[0444] The upper heating plate disclosed herein may include a sensor mounting block on its bottom surface with two thermistor wells (see thermistor well 1211 in FIG. 12A and thermistor well 2011 in FIG. 20B) for housing two thermistors used to measure the temperature of the upper heating plate. The thermistors can measure the upper heating plate temperature in the form of a voltage. The thermistors are arranged in a voltage divider configuration. As the temperature changes, the resistance of the thermistors also changes, and the resistance correlates to a change in voltage. This thermistor voltage is sent to the ADC input of a microcontroller (such as the controller disclosed herein). The voltage is then directly converted to a temperature value using a mathematical function, such as a polynomial equation. The function can be derived from the resistance-to-temperature relationship given in the datasheet for the thermistor and the voltage divider circuit used. Therefore, only one step may be required to determine the temperature value. While the illustrated example uses two thermistors, the temperature measurement can also be performed using a single thermistor. The system can use one thermistor and a second thermistor as a redundant sensor, or the controller can use the average temperature value of the two temperature sensors.

[0445] Heat contributions to the thermistor from materials of the heater plate assembly other than the upper heating plate can result in an inaccurate reading. To ensure that the thermistor temperature measurement is more representative of the temperature of the upper heating plate, a safety feature (see, e.g., safety feature 950 in FIGS. 9 and 9A-9D and safety feature 2050 in FIGS. 20A-20C) can be placed on the lower plate to isolate the thermistor from external heat contributions. The safety feature can be a thermal cutoff unit. The thermal cutoff unit is a hardware device that cuts off power to the heater plate when one or more conditions indicative of unsafe operation are detected by one or more sensors, for example, when the heater plate temperature exceeds a threshold value. The safety feature can irreversibly disable the supply of power to the heater plate in the event of a failure of software or other protection circuitry implemented in the heater plate assembly hardware. Alternatively, the thermal cutoff unit can be a resettable hardware unit that can be reset by the user. The thermal cutoff unit may have an accessible switch, button, or actuator that can be used to reset the hardware circuitry. The safety feature can provide additional protection against system failure. The safety feature can be secured to the bottom plate using, for example, two screws or other types of fastening or securing mechanisms.

[0446] The safety feature primarily responds to the temperature of the upper heating plate, which contacts the base of the humidification chamber. This ensures the accuracy of the safety feature and reduces and / or prevents malfunction of the safety feature. However, the heating filament, which may include nichrome wire, can externally affect the reliability and / or proper operation of the safety feature. To reduce the effect of the heating filament, an L-shaped slot can be included in the lower plate that extends slightly beyond the boundary of the heating filament to reduce the thermal contribution of the heating filament to the safety feature. An exemplary lower plate 1920 with an L-shaped slot 1921 is shown in FIGS. 19A-19F. The slot 1921 can have any shape other than an L-shape. The L-shaped slot 1921 can increase the separation distance between the safety feature 2050, shown in simplified form in FIGS. 20A-20C, and the boundary edge 2031 of the heating filament. The safety feature 2050, such as a thermal cutoff unit, can be placed on a platform. The platform can be used to mount the safety feature. 19A-19E, the platform includes two holes 1923 adjacent to the L-shaped slot 1921. The two holes 1923 can allow for the use of screws to secure the safety feature 2050 to the bottom plate 1920.

[0447] The increased separation distance can help ensure that the safety feature 2050 experiences a substantially constant thermal energy distribution and is not activated by "transient" contributions (such as from a heating filament). The L-shaped slot 1921 reduces metal between the safety feature 2050 and the bottom plate 1920, such as by removing some conductive paths from the bulk of the bottom plate 1920 and the safety feature 2050, without compris- ing the structural integrity of the bottom plate 1920. Additionally, small steps 1922 may be machined into the long edges of the L-shaped slot (shown by the shaded area in FIG. 19C and also shown in FIGS. 20A-20C) to further increase the separation between the safety feature 2050 and the bottom plate 1920 and further reduce noise in the safety feature 2050 due to heat within the bottom plate 1920. The increased separation prevents heat contribution from the heating filament to the L-shaped slot 1921 and false activation of the safety feature 2050.

[0448] An insulating sheet as described herein, such as a mica sheet and / or a thermal interface material, can function to transfer heat from the heating filament to the lower plate. Thus, as shown by the dashed circle in FIG. 20A, the L-shaped slot 1921 can extend beyond the boundary edge 2041 of the insulating sheet, further reducing the thermal contribution from the insulating sheet to the safety feature.

[0449] Alternatively, as shown in FIGS. 18C and 18D , the overall thickness of the lower plate 1820 can be reduced, for example, compared to the lower plate shown in FIGS. 12D and 12E , while leaving a platform 1852 protruding from the remainder of the lower plate 1820. For example, but not by way of limitation, the overall thickness can be reduced to about 2 mm to about 9 mm, or about 3 mm to about 4 mm, or about 3 mm. The platform 1852 can protrude from the remainder of the lower plate 1820 by, for example, but not by way of limitation, about 1 mm to about 3 mm, or about 2 mm. The thickness of the lower plate 1820 at the platform 1852 can be, for example, but not by way of limitation, about 4 mm to about 10 mm, or about 4 mm to about 6 mm, or about 5 mm. A safety feature can be disposed on the platform 1852. The platform 1852 can be created or defined by thinning the remainder of the lower plate 1820. Alternatively, the platform may be defined within a receptacle formed in the lower plate. The platform 1852 may provide sufficient screw or other fastening tool depth to improve securement of the safety feature to the lower plate 1820. The platform 1852 may also improve decoupling of the thermistor by increasing the thermal mass of the area surrounding the safety feature. In other words, the platform 1852 may attenuate unwanted effects of the heating filament on the safety feature.

[0450] Alternatively, as shown in Figures 21A-21F and 22A-22B, the features of lower plate 1820 can be combined with the features of lower plate 1920 to have lower plate 2120 including platform 2152 and L-shaped slot 2121. As shown in Figures 21A and 21E, slot 2121 can be located around the edge of platform 2152. Steps along the long sides of slot 2121 (such as step 1922 of lower plate 1920) are not shown, although such steps may optionally be included in lower plate 2120. Slot 2121 can also have any shape other than L-shaped.

[0451] 22A-22B, a portion of safety feature 2250 has its lower surface not supported by platform 2152. This does not affect the performance of the safety feature, as this unsupported portion is not coupled to a fastening screw or other fastening tool and serves primarily to further stabilize safety feature 2250.

[0452] The heater plate assemblies shown in Figures 20A-20C and 22A-22B can contain two insulating layers of thermal interface material, such as Layer A and Layer B shown in Figure 12A. Insulating layer A and / or insulating layer B may have a thickness of, for example, but not limited to, between about 0.002" (0.05 mm) or about 0.04" (1.02 mm), or about 0.002" (0.05 mm), about 0.003" (0.08 mm), about 0.005" (0.13 mm), about 0.006" (0.15 mm), about 0.009" (0.23 mm), about 0.012" (0.31 mm), about 0.015" (0.38 mm), about 0.016" (0.41 mm), about 0.018" (0.46 mm), about 0.02" (0.51 mm), about 0.025" (0.64 mm), about 0.03" (0.76 mm), or about 0.04" (1.02 mm).

[0453] The separation distance between the thermistor and the lower plate can also be increased to make the thermistor temperature readings more representative of the temperature of the upper heating plate. The greater the separation between the thermistor and the lower plate, the less heat contribution from the lower plate to the thermistor readings, and the more accurate and reliable the temperature of the upper heating plate can be obtained by the thermistor.

[0454] For example, the thickness of the lower plate can be reduced in certain areas to provide a greater separation between the lower plate and the thermistor disposed on the bottom surface of the upper heating plate. Exemplary thickness reductions are shown in Figures 19B-19C, 20A-20C, 21A, and 21E. The thickness reduction can result in a stepped portion 1925, 2125 being formed on the bottom surface of the lower plate 1920, 2120. The stepped portion can further thermally isolate the lower plate from the thermistor.

[0455] To increase the separation between the lower plate and thermistor, the upper heating plate sensor mounting block, such as the upper heating plate sensor mounting block 2010 of FIGS. 20B and 20C, can also be reduced in size (e.g., width and / or length) when compared to, for example, the upper heating plate sensor mounting block 1210 shown in FIG. 12A. For example, the smaller sensor mounting blocks of FIGS. 20B and 20C can have a thickness of about 3 mm to about 9 mm, or about 5 mm to about 7 mm. The total height of the upper heating plate 2010, including the sensor mounting block, can be about 6 mm to about 15 mm, or about 8 mm to about 11 mm, or about 9 mm to about 10 mm. The total height of the upper heating plate 2010, including the sensor mounting block and raised lip of the upper heating plate 2010, at its thickest point can be about 10 mm to about 12 mm, or about 11.5 mm.

[0456] Reducing the sensor mounting block size allows for a reduced amount of metal to better isolate the thermistor from extraneous heating sources and / or potential direct contact with the heating filament. A smaller sensor mounting block also allows for a better thermal coupling of the thermistor to the upper heating plate. Additionally, a smaller sensor mounting block allows the sensor mounting block to be spaced farther from the lower plate to avoid errors due to temperature changes in the lower plate.

[0457] term Examples of respiratory humidification systems and related components and methods have been described with reference to the figures. The figures illustrate various systems and modules and the connections between them. The various modules and systems can be combined in various configurations, and the connections between the various modules and systems may represent physical or logical links. The representations in the figures are presented for clarity of the principles, and details regarding the division of modules or systems are provided for ease of explanation rather than for the purpose of detailing separate physical embodiments. The examples and illustrations are intended for illustrative purposes and do not limit the scope of the inventions described herein. For example, the principles herein may be applied to other types of humidification systems, including surgical humidifiers, as well as respiratory humidifiers. The principles herein may be applied to respiratory applications and other scenarios for determining whether water is available in a respiratory system.

[0458] As used herein, the term “processor” broadly refers to any suitable device, logic block, module, circuit, or combination of elements for executing instructions. For example, controller 8 may include any conventional general-purpose single- or multi-chip microprocessor, such as a Pentium® processor, a MIPS® processor, a Power PC® processor, an AMD® processor, an ARM® processor, or an ALPHA® processor. Additionally, controller 122 may include any conventional special-purpose microprocessor, such as a digital signal processor or a microcontroller. The various illustrative logic blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or executed with a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein, or pure software within a main processor. For example, logic module 504 may be a software-implemented functional block that does not utilize any additional and / or specialized hardware elements. The controller 8 may be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a combination of a microcontroller and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0459] Data storage can refer to electronic circuitry that allows data to be stored and retrieved by a processor. Data storage can refer to external devices or systems, such as disk drives or solid-state drives. Data storage can also refer to solid-state semiconductor storage (chips), such as random access memory (RAM) or various forms of read-only memory (ROM), that are connected directly to a communication bus or to the controller 8. Other types of data storage include bubble memory and core memory. Data storage can be physical hardware configured to store data on a non-transitory medium.

[0460] Although specific embodiments and examples are disclosed herein, the subject matter of the present invention extends to other alternative embodiments and / or uses other than those specifically disclosed, as well as modifications and equivalents thereof. Accordingly, the scope of the claims or embodiments appended hereto is not limited by any of the specific embodiments described herein. For example, in any method or process disclosed herein, the acts or operations of the method or process may be performed in any suitable order and are not necessarily limited to any particular disclosed order. Various operations may be described sequentially as multiple separate operations, as this may be useful in understanding particular embodiments. However, the order of description should not be construed as implying that these operations are order-dependent. Furthermore, structures described herein may be embodied as integrated components or as separate components. For purposes of comparing various embodiments, certain aspects and advantages of these embodiments are described. Not all such aspects or advantages are necessarily achieved by any particular embodiment. Thus, for example, various embodiments may be practiced in a manner that achieves or optimizes one advantage or group of advantages taught herein without necessarily achieving other aspects or advantages that may also be taught or suggested herein.

[0461] As used herein, conditional language such as, inter alia, "can," "could," "might," "may," "eg," and the like, unless otherwise stated or understood within the context of use, is intended to generally convey that certain embodiments include particular features, elements, and / or conditions, while other embodiments do not include particular features, elements, and / or conditions. Thus, such conditional language does not generally imply that one or more embodiments require a feature, element, and / or condition. As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," or any other variation thereof, are intended to include a non-exclusive inclusion. For example, a process, method, article, or apparatus that includes a list of elements is not necessarily limited to only those elements and may include other elements not expressly listed or inherent in such process, method, article, or apparatus. Also, the term "or" is used in its inclusive (rather than its exclusive) sense, for example, when used to connect a list of elements, so that the term "or" refers to one, some, or all of the elements in the list. Connecting terms such as "at least one of X, Y, and Z" are understood in their common context to convey that an item, term, etc. can be either X, Y, or Z, unless otherwise indicated. Thus, such connecting terms do not generally imply that a particular embodiment requires that at least one X, at least one Y, and at least one Z, respectively, be present. As used herein, the terms "about" or "approximately" can mean that a value is within ±10%, ±5%, or ±1% of the stated value.

[0462] The methods and processes described herein may be embodied in, and partially or fully automated via, software code modules executed by one or more general-purpose and / or special-purpose computers. The term "module" refers to logic embodied in hardware and / or firmware, or a collection of software instructions, possibly with entry and exit points, written in a programming language such as C or C++. Software modules may be compiled and linked into an executable program, installed in a dynamically linked library, or written in an interpreted programming language such as BASIC, Perl, or Python. It will be understood that software modules may be callable from other modules or from themselves, and / or may be invoked in response to detected events or interrupts. Software instructions may be embedded in firmware, such as erasable programmable read-only memory (EPROM). It will further be understood that hardware modules may include connected logic units, such as gates and flip-flops, and / or may include programmable units, such as programmable gate arrays, application-specific integrated circuits, and / or processors. The modules described herein may be implemented as software modules, but may also be represented in hardware and / or firmware. Further, in some embodiments, the modules may be separately compiled, while in other embodiments, the modules may represent a subset of instructions of a separately compiled program and may not have an interface available to other logical program units.

[0463] In particular embodiments, code modules may be embodied in and / or stored on any type of computer-readable medium or other computer storage device. In some systems, data (and / or metadata) input to the system, data generated by the system, and / or data used by the system may be stored in any type of computer data repository, such as a relational database and / or a flat file system. Any of the systems, methods, and processes described herein may include interfaces configured to enable interaction with users, operators, other systems, components, programs, etc.

[0464] It should be emphasized that many variations and modifications may be made to the embodiments described herein, and these elements should be understood to be particularly permissible examples. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims. Moreover, nothing in the foregoing disclosure should be construed as implying that any particular component, feature, or process step is required or essential.

[0465] As used herein, a value from which a parameter may be inferred suggests a relationship between the value and the parameter, but does not necessarily indicate a direct correlation between the value and the parameter. However, the term "a parameter may be inferred" should be interpreted broadly enough to encompass a direct correlation between a value and a parameter, such that the parameter may be derived directly from the value from which the parameter may be inferred.

Claims

1. 1. A multi-layer heater plate assembly for a respiratory humidifier, comprising: An upper heating plate; a heating element configured to generate heat, the heating element being located below the upper heating plate; a thermal interface layer between the upper heating plate and the heating element, the thermal interface layer comprising a compliant thermal interface material configured to displace an air gap between the upper heating plate and the heating element; a multi-layer heater plate assembly including:

2. 10. The multi-layer heater plate assembly of claim 1, wherein the thermal interface layer is configured to displace an air gap between the upper heating plate and the heating element to improve thermal conductivity between the upper heating plate and the heating element.

3. 3. The multi-layer heater plate assembly of claim 1, including a lower plate, wherein the heating element is defined by the upper heating plate and the lower plate.

4. The multi-layer heater plate assembly of any one of claims 1 to 3, wherein the thermal interface layer comprises a thickness sufficient to provide electrical insulation.

5. The multi-layer heater plate assembly of any one of claims 1 to 4, removably coupled to one another by one or more fasteners.

6. 6. The multi-layer heater plate assembly of claim 1, formed by bolting the lower plate to the upper heating plate with the heating element and the electrical insulation layer between the lower plate and the upper heating plate.

7. The multi-layer heater plate assembly of any one of claims 1 to 6, wherein the upper heating plate includes a sensor mounting block configured to receive at least one temperature sensor.

8. The multi-layer heater plate assembly of claim 7 , wherein the sensor mounting block is configured to receive two temperature sensors.

9. 9. The multi-layer heater plate assembly of claim 7 or 8, wherein the at least one temperature sensor includes a thermistor.

10. The multi-layer heater plate assembly of any one of claims 3 to 10, further comprising a safety feature coupled to the bottom plate.

11. The multi-layer heater plate assembly of claim 10 , wherein the safety feature includes a thermal cutoff unit.

12. 12. The multi-layer heater plate assembly of claim 10 or 11, wherein the bottom plate includes a platform for supporting the safety feature.

13. The multi-layer heater plate assembly of claim 12 , wherein the safety feature is secured to the platform by a screw.

14. 14. The multi-layer heater plate assembly of claim 12 or 13, wherein the platform protrudes from the remainder of the bottom plate.

15. 15. The multi-layer heater plate assembly of claim 10, wherein the bottom plate includes slots where the safety features are bonded to the bottom plate to improve isolation of the safety features from the heating element.

16. The multi-layer heater plate assembly of claim 15 , wherein the bottom plate further includes a cutout step along the length of the slot.

17. 17. The multi-layer heater plate assembly of claim 15 or 16, wherein the slot is L-shaped.

18. The multi-layer heater plate assembly of any one of claims 15 to 17, wherein the slots terminate at or near the periphery of the heating element.

19. The multi-layer heater plate assembly of any one of claims 15 to 18, wherein the slots extend radially outward beyond a periphery of the thermal interface layer.

20. The multi-layer heater plate assembly of any one of claims 10 to 19, wherein the bottom plate includes a cutout step adjacent the sensor mounting block when the heater plate assembly is assembled.

21. The multi-layer heater plate assembly of any one of claims 1 to 20, wherein the thermal interface layer has a hardness scale of 50-100 Shore 00.

22. 22. The multi-layer heater plate assembly of claim 21, wherein the thermal interface layer has a hardness of 80 on the Shore 00 scale.

23. The multi-layer heater plate assembly of any one of claims 1 to 22, further comprising at least one non-flexible electrically insulating layer.

24. 24. The multi-layer heater plate assembly of claim 23, wherein the at least one non-flexible electrically insulating layer comprises mica.

25. The multi-layer heater plate assembly of any one of claims 1 to 24, wherein the thermal interface material is electrically insulating.

26. 26. The multi-layer heater plate assembly of claim 1, further comprising a second thermal interface layer, the second thermal interface layer comprising a compliant thermal interface material configured to displace air gaps between components of the multi-layer heater plate assembly.

27. 27. The multi-layer heater plate assembly of claim 26, wherein the second thermal interface layer is located between the heating element and the bottom plate.

28. 27. The multi-layer heater plate assembly of claim 26, wherein the second thermal interface layer is located between the upper heating plate and the lower plate.

29. 30. The multi-layer heater plate assembly of claim 28, wherein said second thermal interface layer is electrically conductive.

30. The multi-layer heater plate assembly of any one of claims 1 to 29, wherein the compliant thermal interface material comprises a silicone or a silicone compound.

31. 31. The multi-layer heater plate assembly of claim 1, wherein the compliant thermal interface material comprises a fiberglass substrate and a thermally conductive material embedded in or disposed on the substrate.

32. The multi-layer heater plate assembly of any one of claims 1 to 31, wherein the compliant thermal interface material has a breakdown voltage of at least 4000V AC.

33. 33. The multi-layer heater plate assembly of claim 32, wherein the compliant thermal interface material has a breakdown voltage of at least 6000V AC.

34. The multi-layer heater plate assembly of any one of claims 1 to 33, wherein the compliant thermal interface material has a thermal conductivity of at least 1.8 W / (mK).

35. The multi-layer heater plate assembly of any one of claims 1 to 34, wherein the compliant thermal interface material is elastic.

36. 1. A multi-layer heater plate assembly for a respiratory humidifier, comprising: An upper heating plate; A lower plate; a heating element configured to generate heat, the heating element being defined by the upper heating plate and the lower plate; a compliant thermal interface layer between the lower plate and the upper heating plate, the compliant thermal interface layer being configured to displace an air gap between the lower plate and the upper heating plate; a multi-layer heater plate assembly including:

37. 37. The multi-layer heater plate assembly of claim 36, removably coupled to one another by one or more fasteners.

38. 38. The multi-layer heater plate assembly of claim 36 or 37, formed by bolting the lower plate to the upper heating plate with the heating element and the electrical insulation layer between the lower plate and the upper heating plate.

39. The multi-layer heater plate assembly of any one of claims 36 to 38, wherein the upper heating plate includes a sensor mounting block configured to receive at least one temperature sensor.

40. 40. The multi-layer heater plate assembly of claim 39, wherein the sensor mounting block is configured to receive two temperature sensors.

41. 41. The multi-layer heater plate assembly of claim 39 or 40, wherein the at least one temperature sensor comprises a thermistor.

42. 42. The multi-layer heater plate assembly of any one of claims 36 to 41, wherein the compliant thermal interface layer is configured to displace an air gap between an edge of the lower plate and the upper heating plate.

43. The multi-layer heater plate assembly of any one of claims 36 to 42, wherein the compliant thermal interface layer is electrically insulating.

44. 44. The multi-layer heater plate assembly of any one of claims 36 to 43, including a second thermal interface layer configured to displace an air gap between the upper heating plate and the heating element.

45. The multi-layer heater plate assembly of any one of claims 36 to 44, further comprising at least one non-flexible electrically insulating layer.

46. 46. ​​The multi-layer heater plate assembly of claim 45, wherein said at least one non-flexible electrically insulating layer comprises mica.

47. 47. The multi-layer heater plate assembly of claim 45 or 46, wherein the at least one inflexible electrically insulating layer is located between the compliant thermal interface layer and the heating element.

48. 48. The multi-layer heater plate assembly of any one of claims 45 to 47, wherein the at least one inflexible, electrically insulating layer is located between the heating element and the bottom plate.

49. 1. A humidifier system for use in a medical procedure, comprising: A base unit; a humidifier chamber receivable on the base unit; Including, The base unit includes a multi-layer heater plate assembly according to any one of claims 1 to 48. system.

50. 50. The system of claim 49, wherein the humidifier chamber includes a conductive base, the conductive base being forced into contact with the heater plate assembly when the humidifier chamber is placed on the base unit.

51. 51. The system of claim 49 or 50, wherein the heater plate assembly heats the humidifier chamber to heat the contents of the chamber to humidify gases passing through the chamber.

52. 52. The system of any one of claims 49 to 51, further comprising a tube configured to carry gas from the humidifier chamber to a patient interface.

53. 1. A humidifier system for use in a medical procedure, comprising: a housing configured to receive a humidifier chamber; a heater plate assembly located at least partially within the housing, the heater plate assembly comprising: an upper heating plate configured to contact a base of the humidifier chamber when the humidifier chamber is received by the housing; and a thermistor located on or near the upper heating plate; a heating element configured to generate heat; an electrical isolation mechanism between the upper heating plate and the heating element; a heater plate assembly including: Including, the electrical isolation mechanism thermally couples the heating element and the upper heating plate such that heat generated by a power signal to the heating element is transferred to the upper heating plate; the electrical isolation mechanism improves thermal coupling between the heating element and the upper heating plate; Humidifier system.

54. 54. The system of claim 53, wherein the electrical isolation mechanism comprises a flexible and / or resilient insulating sheet.

55. 55. The system of claim 53 or 54, wherein the electrical isolation mechanism includes a compliant insulating sheet configured to displace an air gap between the upper heating plate and the heating element.

56. 56. The system of any one of claims 53 to 55, wherein the electrically insulating sheet improves heat conduction from the heating element to the upper heating plate.

57. 57. The system of any one of claims 53 to 56, wherein the electrically insulating sheet reduces capacitance of the heater plate assembly so as to improve thermal conductivity between components of the heater plate assembly.

58. 58. The system of any one of claims 53 to 57, further comprising a double electrical insulation mechanism comprising two insulating elements, said two insulating elements comprising two non-flexible insulating layers.

59. 60. The system of claim 58, wherein the two non-flexible insulating layers comprise mica.

60. 60. The system of claim 58 or 59, wherein the two insulating elements comprise two layers separate from each other.

61. 61. The system of any one of claims 58 to 60, wherein the double electrical isolation mechanism is located between the electrical isolation mechanism and the heating element.

62. 62. The system of any one of claims 53 to 61, wherein the electrical isolation mechanism comprises a thermally conductive but electrically insulating elastomer.

63. 63. The system of any one of claims 53 to 62, wherein the electrical insulating mechanism comprises a silicone or silicone compound.

64. 64. The system of any one of claims 53 to 63, wherein the electrical isolation mechanism includes a fiberglass substrate and a thermally conductive material embedded in or disposed on the substrate.

65. 65. The system of any one of claims 53 to 64, wherein the electrical isolation mechanism comprises a material having a breakdown voltage of at least 4000V AC.

66. 66. The system of claim 65, wherein the electrical isolation feature comprises a material having a breakdown voltage of at least 6000V AC.

67. 67. The system of any one of claims 53 to 66, wherein the electrical isolation mechanism comprises a material having a thermal conductivity of at least 1.8 W / (m.K).

68. 68. A system as described in any one of claims 53 to 67, wherein the electrical isolation mechanism improves thermal coupling between the heating element and the upper heating plate such that the waveform applied to the power signal to detect a low or out of water condition in the humidifier chamber can be a reduced power waveform.

69. 69. A system as described in any one of claims 53 to 68, wherein the electrical isolation mechanism improves thermal coupling between the heating element and the upper heating plate so that the temperature reading of the thermistor better corresponds to the temperature of the water in the humidifier chamber.

70. 70. The system of any one of claims 53 to 69, wherein the heater plate assembly includes a lower plate, the heating element and the electrical isolation mechanism being defined between the lower plate and the upper heating plate.

71. 71. The system of claim 70, wherein the bottom plate is in contact with the electrical isolation mechanism.

72. 71. The system of claim 70, wherein the heater plate assembly includes a flexible, electrically insulating sheet between the upper heating plate and the lower plate.

73. 73. The system of any one of claims 70-72, wherein the heater plate assembly includes a compliant electrically insulating sheet between the upper heating plate and the lower plate configured to displace an air gap between the upper heating plate and the lower plate.

74. 1. A respiratory or surgical humidifier system comprising: A base unit, a heater plate including one or more heating elements; a hardware controller in electronic communication with the one or more heating elements of the heater plate and configured to energize the one or more heating elements of the heater plate; a base unit including: a humidifier chamber defining a volume and including a conductive base, the conductive base being receivable on the base unit such that the conductive base contacts the heater plate, the humidifier chamber being configured to hold a water level; Including, the hardware controller is configured to determine a value from which a specific heat capacity of the humidifier chamber can be inferred and to determine a low water or out of water condition based at least in part on the determined value from which the specific heat capacity can be inferred. Respiratory or surgical humidifier systems.

75. 75. The respiratory or surgical humidifier system of claim 74, wherein the hardware controller determines that a low water or out of water condition exists in response to the determined value from which the specific heat capacity can be inferred being less than a threshold value.

76. 76. A respiratory or surgical humidifier system as described in claim 74 or 75, wherein the hardware controller continuously determines the value from which the specific heat capacity can be inferred.

77. 77. A respiratory or surgical humidifier system according to any one of claims 74 to 76, wherein the hardware controller intermittently determines the value from which the specific heat capacity can be inferred.

78. 78. A respiratory or surgical humidifier system according to any one of claims 74 to 77, wherein the value by which the specific heat capacity can be inferred is determined as a numerical score.

79. 79. A respiratory or surgical humidifier system according to any one of claims 74 to 78, including a temperature sensor coupled to or adjacent to the heater plate, the temperature sensor determining the temperature of the heater plate.

80. 80. The respiratory or surgical humidifier system of claim 79, wherein the temperature sensor includes a thermistor.

81. 80. A respiratory or surgical humidifier system as described in claim 79, wherein the temperature sensor includes two thermistors, each acting as a voltage divider.

82. 82. The respiratory or surgical humidifier system of claim 81, wherein the hardware controller determines a temperature value from voltage readings of the two thermistors.

83. 83. A respiratory or surgical humidifier system according to any one of claims 74 to 82, wherein the hardware controller determines a value from which the specific heat capacity can be estimated based on the temperature reading of the temperature sensor.

84. The hardware controller applying a characteristic energization signal to the one or more heating elements of the heater plate; processing a temperature signal from the temperature sensor corresponding to the characteristic energization signal; determining the value from which the specific heat capacity can be inferred based on the temperature signal; and outputting a low water or water shortage warning in response to the determined value from which the specific heat capacity can be estimated being less than a threshold value.

84. A respiratory or surgical humidifier system as claimed in any one of claims 74 to 83, configured as follows:

85. 85. A respiratory or surgical humidifier system according to claim 84, wherein the hardware controller is configured to apply the characteristic energization signal continuously and / or intermittently.

86. 86. A respiratory or surgical humidifier system according to claim 84 or 85, wherein the hardware controller is configured to apply the characteristic energization signal to a heater plate control signal.

87. 87. The respiratory or surgical humidifier system of claim 86, wherein the hardware controller is configured to inject the characteristic energization signal into the heater plate control signal.

88. A respiratory or surgical humidifier system according to any one of claims 84 to 87, wherein the characteristic energization signal has a higher frequency than the heater plate control signal.

89. 89. A respiratory or surgical humidifier system as described in any one of claims 84 to 88, wherein the hardware controller passes the temperature measurement value of the temperature sensor through a bandpass filter having a filter frequency corresponding to the frequency of the characteristic energization signal so as to pass the temperature measurement value corresponding to the frequency of the characteristic energization signal.

90. 90. The respiratory or surgical humidifier system of claim 89, wherein the temperature measurements corresponding to the frequencies of the characteristic energization signal are used to determine the value from which the specific heat capacity can be inferred.

91. The system of any one of claims 74 to 90, wherein the heater plate comprises a multi-layer heater plate assembly according to any one of claims 1 to 48.

92. 1. A respiratory or surgical humidifier system comprising: A base unit, a heater plate including one or more heating elements; a hardware controller in electronic communication with the one or more heating elements of the heater plate and configured to energize the one or more heating elements of the heater plate; a temperature sensor coupled to or adjacent to the heater plate, the temperature sensor configured to generate a signal indicative of the temperature of the heater plate; a base unit including: a humidifier chamber defining a volume and including a conductive base, the conductive base being receivable on the base unit such that the conductive base contacts the heater plate, the humidifier chamber being configured to hold a water level; Including, The hardware controller applying a characteristic energization signal to the one or more heating elements of the heater plate; receiving a signal indicative of a response to the characteristic energization signal; determining a low water or out of water condition based on the magnitude and / or phase of the received signal indicative of the response to the characteristic energization signal; A respiratory or surgical humidifier system configured to:

93. 93. A respiratory or surgical humidifier system as described in claim 92, wherein the determined magnitude above a threshold indicates a low water or out of water condition.

94. 94. A respiratory or surgical humidifier system as described in claim 92 or 93, wherein the determined magnitude and / or phase meeting a threshold is indicative of a low water or out of water condition.

95. 95. A respiratory or surgical humidifier system as described in claim 94, wherein the determined magnitude and / or phase being outside or within a predetermined region of the two-dimensional representation of the magnitude and / or phase indicates a low water or out of water condition.

96. A respiratory or surgical humidifier system according to any one of claims 92 to 95, wherein the size is inversely proportional to the specific heat capacity of the humidifier chamber.

97. 97. A respiratory or surgical humidifier system according to any one of claims 92 to 96, wherein the hardware controller is configured to apply the characteristic energization signal at a characteristic frequency.

98. 98. A respiratory or surgical humidifier system as described in claim 97, wherein the characteristic frequency is greater than a heater plate control operating frequency at which the hardware controller energizes the one or more heating elements of the heater plate.

99. 99. A respiratory or surgical humidifier system as described in claim 98, wherein the characteristic energization signal has a frequency at least 1.5 times the heater plate control operating frequency.

100. A respiratory or surgical humidifier system according to any one of claims 92 to 99, wherein the hardware controller includes a signal generator configured to generate and apply the characteristic energization signal.

101. A respiratory or surgical humidifier system according to any one of claims 92 to 100, wherein the hardware controller is configured to inject the characteristic energization signal into the heater plate control signal.

102. A respiratory or surgical humidifier system as described in any one of claims 92 to 101, wherein the hardware controller includes a filter that filters a signal indicative of the temperature of the heater plate to obtain the signal indicative of the response to the energization signal.

103. 103. A respiratory or surgical humidifier system as described in claim 102, wherein the filter is a bandpass filter.

104. 104. The respiratory or surgical humidifier system of claim 103, wherein the bandpass filter filters the signal indicative of the temperature of the heater plate within a band corresponding to the frequency of the characteristic energization signal.

105. 105. The respiratory or surgical humidifier system of claim 104, wherein the magnitude of the signal indicative of the temperature of the heater plate exceeding a threshold at the frequency of the characteristic energization signal indicates a low water or out of water condition.

106. 93. The respiratory or surgical humidifier system of claim 92, wherein the received signal includes a frequency response of the signal indicative of the temperature of the heater plate, and wherein the hardware controller is configured to determine a low water or out of water condition based on the frequency response.

107. 107. A respiratory or surgical humidifier system as described in any one of claims 92 to 106, wherein the magnitude of the received signal indicative of the response to the characteristic energization signal is processed to determine a score, and if the score is above a threshold, the score indicates a low water or out of water condition.

108. The system of any one of claims 92 to 107, wherein the heater plate comprises a multi-layer heater plate assembly according to any one of claims 1 to 48.

109. 1. A method for detecting a low or empty water condition in a humidifier chamber of a respiratory or surgical humidifier system, comprising: using a hardware controller in a base unit of the respiratory or surgical humidifier system; determining a value by which a specific heat capacity of the humidifier chamber can be estimated, the humidifier chamber defining a volume and capable of holding a water level, the humidifier chamber including a conductive base, the conductive base being receivable on the base unit such that the conductive base contacts a heater plate of the base unit, the heater plate including one or more heating elements, the one or more heating elements being in electronic communication with the hardware controller and configured to be energized by the hardware controller; determining a low-water or out-of-water condition based at least in part on the determined value from which the specific heat capacity can be inferred; and A method comprising:

110. 1. A method for detecting a low or empty water condition in a humidifier chamber of a respiratory or surgical humidifier system, comprising: using a hardware controller in a base unit of the respiratory or surgical humidifier system; applying a characteristic energization signal to one or more heating elements of a heater plate in the base unit, the one or more heating elements of the heater plate being in electronic communication with the hardware controller and configured to be energized by the hardware controller; the respiratory or surgical humidifier system further comprising a humidifier chamber defining a volume and including a conductive base, the conductive base being receivable on the base unit such that the conductive base contacts the heater plate, the humidifier chamber being capable of holding a water level; receiving a signal indicative of a response to the characteristic energization signal from a temperature sensor coupled to or adjacent to the heater plate; determining a low water or out of water condition based on the magnitude and / or phase of the received signal indicative of the response to the characteristic energization signal; A method comprising:

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