System and method for reducing CO2 rebreathing from positive airway pressure machines

Abstract

A positive airway pressure (PPR) device includes a pressure generator, a mask configured to be positioned over the patient's face, a conduit operably connecting the pressure generator to the mask, and an exhaust port. A method for reducing CO2 rebreathing from a PPR machine includes supplying pressure into the patient's airway via the conduit and mask over a treatment period including multiple inhalation and multiple exhalation periods, the supplied pressure being at a level sufficient to expel most of the patient's exhaled air through the exhaust port, and during the exhalation period, if it is determined that some of the patient's exhaled air is flowing into the conduit, the pressure is increased to remove the patient's exhaled air from the conduit via the exhaust port.

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims priority to U.S. Provisional Application No. 63 / 462856, filed on April 28, 2023; U.S. Provisional Application No. 63 / 499412, filed on May 1, 2023; and U.S. Provisional Application No. 63 / 588467, filed on October 6, 2023, the entire disclosures of which are hereby incorporated herein by reference.

[0002] The subject matter of the present disclosure relates to airway positive pressure systems and methods for treating sleep - breathing disorders such as, for example, obstructive sleep apnea. In particular, the systems and methods of the present invention are configured to reduce the amount of CO2 exhaled by a patient, retained within the system, and subsequently rebreathed by the patient during the patient's next inhalation.

Background Art

[0003] Sleep apnea is a potentially serious disorder in which breathing repeatedly stops or starts during sleep. Some estimates state that over 25% of adults between the ages of 30 and 70 have sleep apnea, and that the number reaches 90% in older men.

[0004] One of the most common treatments for sleep apnea is continuous positive airway pressure (CPAP) therapy. During treatment, a CPAP machine delivers airflow through a circuit, i.e., a tube terminated with a mask or intranasal pillow mask connected to the patient. This airflow increases the air pressure in the patient's throat, preventing its airway from becoming obstructed. Subsequent generations of positive airway pressure therapy have been designed to reduce pressure at the start of the exhalation phase (typically 5-15 cmH2O) in an attempt to improve patient comfort. Because two different pressures are supplied, these systems are commonly referred to as biphasic positive airway pressure (BPAP) therapy. Further research and development have resulted in a wide variety of positive airway pressure machines, but in all cases, positive airway pressure generates airflow through the machine, which interacts with the airflow generated by the patient during inhalation and exhalation. This creates a dynamic flow environment within the circuit. Existing positive airway pressure machines include various valves and ports to control and guide the airflow through the system. However, there remains a need for improved positive airway pressure systems that provide patients with appropriate treatment while reducing unnecessary side effects. [Overview of the project] [Means for solving the problem]

[0005] (Summary of the invention) The subject matter of this disclosure relates, for example, to positive airway pressure systems and methods for treating sleep-disordered breathing, such as obstructive sleep apnea. In particular, the systems and methods of the present invention are configured to reduce the amount of CO2 exhaled by the patient, held within the system, and subsequently rebreathed during the patient's next inhalation.

[0006] In some exemplary embodiments of the present invention, an airway positive pressure machine is provided, comprising a pressure generator, a mask configured to be positioned over a patient's face, a conduit operably connecting the pressure generator to the mask, and an exhaust port. In some exemplary implementations, the method of the present invention includes the step of supplying pressure into the patient's airway via the conduit and mask over a therapeutic period comprising multiple inhalation periods and multiple exhalation periods. The supplied pressure is at a level sufficient to expel most of the patient's exhaled air through the exhaust port.

[0007] In some exemplary implementations, the patient inhales less than 0.1% CO2 during each inhalation period.

[0008] In some exemplary implementations, the patient's exhaled air is not present in the conduit at the start of each inhalation period.

[0009] In some exemplary implementations, this method further includes the steps of measuring the volume of the patient's exhaled breath and adjusting the supply pressure so that the majority of the patient's exhaled breath is expelled through the exhaust port.

[0010] In some exemplary implementations, this method further includes the steps of determining that some of the patient's exhaled breath flows into the conduit during the exhalation period, and increasing the pressure to remove the patient's exhaled breath from the conduit through the exhaust port.

[0011] In some specific implementations, the pressure-increasing step involves increasing the pressure supplied at the end of the exhalation period.

[0012] In some specific implementations, the step of increasing the pressure includes increasing the time during the exhalation period in which the increased pressure is supplied.

[0013] In some specific implementations, this method further includes the step of reducing the supplied pressure after the patient's exhaled air has been removed from the conduit via the exhaust port.

[0014] In some specific implementations, the pressure-increasing step involves increasing the pressure supplied during the initial portion of the next inhalation period until the patient's exhaled air is removed from the conduit through the exhaust port.

[0015] In some exemplary implementations, this method includes the step of supplying an initial pressure during a first exhalation period, which is configured to prevent the patient's exhaled breath from entering the conduit. The method then includes the step of reducing the pressure supplied during a continuous exhalation period by a predetermined amount until some of the patient's exhaled breath enters the conduit. If the patient's exhaled breath does not enter the conduit, the method then includes the step of increasing the pressure to a final pressure.

[0016] In some exemplary implementations, this method further includes the steps of receiving data from one or more sensors that measure pressure or flow rate through a conduit, and determining whether a portion of the patient's exhaled breath enters the conduit.

[0017] In some exemplary implementations, this method further includes the steps of determining whether the patient is awake or asleep, supplying a minimum pressure if the patient is awake, and increasing the supplied pressure over a certain ramp period after the patient has fallen asleep.

[0018] In some specific implementations, the minimum pressure is sufficient to ensure that no patient exhaled air is present in the conduit at the start of the inhalation period.

[0019] In some specific implementations, during the pressure-increasing step, the pressure supplied at the end of each exhalation period gradually increases over the continuous exhalation period.

[0020] In some specific implementations, the supplied pressure increases during each exhalation period, reaching a higher pressure some time before the next inhalation period, and during the pressure-increasing step, this higher pressure gradually decreases over the continuous exhalation period.

[0021] In some specific implementation examples, the supplied pressure increases during each exhalation period and reaches a higher pressure during a certain period before the next inhalation period. During the step of increasing the pressure, the period gradually increases over consecutive exhalation periods.

[0022] In some exemplary implementation examples, the pressure is a mild airway positive pressure during a part of the inhalation period including the end of the inhalation period. The pressure is a therapeutic airway positive pressure during a part of the exhalation period including the end of the exhalation period, and the therapeutic airway positive pressure is greater than the mild airway positive pressure. After the end of the exhalation period, the pressure decreases from the therapeutic airway positive pressure to the mild airway positive pressure.

[0023] In some specific implementation examples, this method further includes a step of determining that a part of the patient's exhalation enters the conduit during the exhalation period, and a step of increasing the mild airway positive pressure.

[0024] In some specific implementation examples, this method further includes a step of determining that a part of the patient's exhalation enters the conduit during the exhalation period, and a step of maintaining the therapeutic airway positive pressure over a larger part of the exhalation period.

[0025] In some specific implementation examples, this method further includes a step of determining that a part of the patient's exhalation enters the conduit during the exhalation period, and a step of increasing the therapeutic airway positive pressure.

[0026] In some exemplary implementation examples, this method further includes a step of changing the exhaust port to adjust the maximum exhaust flow rate from the exhaust port.

[0027] In some specific implementation examples, the step of changing the exhaust port includes replacing the exhaust port with one of a plurality of replaceable ports, and each of the replaceable ports has a predetermined exhaust flow rate.

[0028] In some specific implementation examples, the exhaust port includes an exhaust orifice with an adjustable size, and the step of changing the exhaust port includes changing the size of the exhaust orifice.

[0029] In some specific implementation examples, this method further includes the step of providing feedback to the user regarding what changes are required to the exhaust port.

Brief Description of the Drawings

[0030] [Figure 1] It is a schematic diagram of an exemplary positive airway pressure system of the present invention during the inhalation phase of a patient's respiratory cycle. [Figure 2] It is a schematic diagram of the exemplary positive airway pressure system of FIG. 1 during a part of the exhalation phase of a patient's respiratory cycle under the first scenario where the patient's exhalation flow never exceeds the exhaust flow. [Figure 3] It is a schematic diagram of the exemplary positive airway pressure system of FIG. 1 during a part of the exhalation phase of a patient's respiratory cycle under the second scenario where the patient's exhalation flow exceeds the exhaust flow but is removable from the circuit before the next inhalation. [Figure 4] It is a schematic diagram of the exemplary positive airway pressure system of FIG. 1 during a part of the exhalation phase of a patient's respiratory cycle under the third scenario where the patient's exhalation flow exceeds the exhaust flow and is not removed from the circuit before the next inhalation. [Figure 4B] It is a schematic diagram of the exemplary positive airway pressure system of FIG. 4 immediately after the start of the next inhalation phase of a patient's respiratory cycle. [Figure 5] It is an exploded perspective view of an exemplary face mask that can be used in the exemplary positive airway pressure system of FIG. 1. [Figure 6] It is a detailed view of the exhaust assembly shown in a separated state. [Figure 7] It is a process flow diagram of one exemplary implementation of the present invention. [Figure 8] It is a graph showing an example of the applied pressure profile of the positive airway pressure system of the present invention in relation to a graph of a patient's air flow. [Figure 9]This graph shows another example of the applied pressure profile of the positive airway pressure system of the present invention, in relation to a graph of the patient's airflow rate. [Modes for carrying out the invention]

[0031] In most positive airway pressure (PPP) systems, the patient's exhaled breath is guided through at least part of the circuit before being expelled into the environment. Therefore, exhaled gases can remain in the circuit, resulting in the patient rebreathing at least some of the exhaled gases with the next inhalation. When exhaled gases are rebreathed, there are three significant effects: (1) humidity increases with each breath; (2) the oxygen fraction of the inhaled air decreases; and (3) the CO2 fraction of the inhaled air increases. If this is experienced during PPP ventilation, the increased humidity will cause discomfort to the patient. The decreased oxygen can lower oxygen saturation and create a cascade of depleted oxygen, but despite the reduced concentration remaining in the lungs from the start of rebreathing, there is a longer utilization time before oxygen depletion becomes critical due to the affinity and availability of hemoglobin for oxygen. However, the accumulation of CO2 is a major problem in that it is simply trapped in the circuit and its concentration increases rapidly if it cannot be removed. Increased levels of inhaled CO2 can trigger various dangerous physical and physiological reactions. The increased CO2 in the air within the lungs reduces the body's ability to remove CO2 from the blood, causing it to accumulate in the blood and tissues. As a result, the pH level in the blood decreases, triggering increased respiratory force. This is because the body continues to work to remove more CO2 and return the CO2 concentration in the blood to normal levels.

[0032] The subject matter of this disclosure relates, for example, to positive airway pressure systems and methods for treating sleep-disordered breathing, such as obstructive sleep apnea. In particular, the systems and methods of the present invention are configured to reduce CO2 rebreathing during the patient's next inhalation.

[0033] Referring to some exemplary embodiments, specifically Figures 1-4, the positive airway pressure system 200 of the present invention includes a pressure generator 300 for providing a desired air pressure to a patient 600. Specifically, the exemplary pressure generator 300 includes a fan 302 that draws air from the environment and passes it through a flow meter 304. The air is then guided to pass through a humidifier 306 before passing from the pressure generator 300 into a conduit 400, the conduit 400 having an inlet 402 operably connected to the pressure generator 300, an outlet 404 operably connected to the patient's respiratory system, and an exhaust port 406 along the conduit 400, preferably near the outlet 404. Further as will be described later, in some embodiments, the exhaust port 406 is incorporated into the outlet 404 itself. The pressure generator 300 generates a circuit airflow 810 through the conduit 400, and therefore the pressure generator 300 is also referred to as a flow generator. By adjusting the operating speed of the fan 302, the pressure generator 300 can influence the pressure applied to the patient's respiratory system by the system 200. Without departing from the spirit and scope of the invention, other means of adjusting the pressure applied to the patient are also possible. For example, other known pressure adjustment means are adjustable valves located above or near the pressure generator that discharge the airflow generated by the fan.

[0034] Referring specifically to Figure 1, during the inhalation phase of the patient's respiration, the diaphragm 608 descends, expanding the lungs 606, resulting in an inhaled airflow 820 through the nasal cavity 602 and pharynx 604. In contrast, referring to Figures 2-4, during the exhalation phase of the patient's respiration, the diaphragm 608 and lungs 606 of the patient 600 relax, resulting in an exhaled airflow 830 through the pharynx 604 and nasal cavity 602. As used here, the nasal cavity 602 includes the mouth. Also, as used here, the patient 600's "airway" includes the nasal cavity 602, pharynx 604, and lungs 606.

[0035] Referring to Figures 1-4 and also to Figure 5, one exemplary outlet 404 is in the form of a face mask 700 secured to the patient's head via a plurality of straps 702. More specifically, the face mask 700 includes a mask body 710 and a sealing structure 704 surrounding the mask body 710. The sealing structure 704 engages with the patient's face 600 and is configured to provide a seal to prevent or significantly reduce gas leakage near the edges of the mask 700. The exemplary face mask 700 is configured to surround the nose and mouth of the patient 600, but other designs are possible, including masks that surround only the patient's mouth, or masks that surround only the patient's nose. For this purpose, a projection 712 extends forward from the central part of the mask body 710 and is shaped to accommodate the nose and mouth of the patient 600. The projection 712 includes an opening 714 through which gas can easily flow into and around the patient's mouth and nose, providing negligible resistance to the inhaled airflow 820 and the exhaled airflow 830. The opening 714 is configured to operably connect the mask body 710 to the circuit conduit 400 and to the exhaust assembly 720, which supplies gas from the pressure generator to the patient's respiratory system. The cylindrical inner surface of the opening 714 of the mask body 710 is shaped to provide a removable friction fit with the substantially cylindrical mating surface of the exhaust assembly 720. The exhaust assembly 720 itself is removablely connected to the circuit conduit 400 for receiving breathable gas.

[0036] Referring specifically to Figure 6, the exemplary exhaust assembly 720 is a substantially elbow-shaped tubular member formed of a rigid material such as plastic. The exhaust assembly 720 includes a primary inlet 722, a primary outlet 724, and a secondary outlet 726, the secondary outlet 726 corresponding to the exhaust port 406 shown in Figures 1 to 4. The primary inlet 722 is connected to the circuit conduit 400 and receives pressurized gas from the pressure generator 300. The primary outlet 724 is connected to the face mask 700 and, as will be described later, alternately delivers pressurized gas to the patient's respiratory system when the patient inhales and receives the patient's exhaled breath when the patient exhales.

[0037] The secondary outlet 726 is positioned between the primary inlet 722 and the primary outlet 724 and is configured to exhaust gas from the circuit. Therefore, the secondary outlet 726 includes an insert 730 that defines multiple orifices through which gas can flow. The exemplary insert 730 is removable and, as will be further described later, interchangeable with other inserts that define different numbers, sizes, or arrangements of orifices to affect the maximum gas flow rate discharged from the secondary outlet 726. Multiple interchangeable ports may be provided, each providing a predetermined exhaust flow rate.

[0038] The gas discharged via the secondary outlet 726 may, as will be further described later, consist only of the gas flowing in via the primary inlet 722, only the gas flowing in via the primary outlet 724, or a combination of gases from both the primary inlet 722 and the primary outlet 724. The face mask 700 described above is merely illustrative and should be understood to include additional functions without departing from the spirit and scope of the present invention.

[0039] For example, in some embodiments, if the pressure inside the exhaust assembly 720 is below a threshold, the exhaust assembly 720 may allow gas to be introduced through openings other than the primary inlet 722 or the primary outlet 724. Thus, the exhaust assembly 720, and in particular the secondary outlet 726, may have a secondary function as an entrainment valve without departing from the spirit and scope of the invention.

[0040] The exemplary face mask 700 shown in Figure 5 is merely one possible implementation example of the general outlet 404 shown in Figures 1-4, and the secondary outlet 726 of the exhaust assembly 720 shown in Figures 5-6 corresponds to the exhaust port 406 shown in Figures 1-4. Furthermore, in some embodiments, instead of using a face mask such as the exemplary face mask 700 shown in Figure 5, the outlet 404 may be any suitable form for operationally connecting the air supplied by the pressure generator 300 to the patient, for example, a full face mask, a partial face mask, a nasal mask, a nasal pillow mask, or any other suitable outlet, without being limited to the following.

[0041] Referring again to Figures 1 to 4, the exemplary airway pressure system 200 further comprises a controller 500 for controlling the pressure applied to the patient's airway. The controller 500 includes a computer with a processor for executing instructions stored in a memory component and adjusting the pressure applied to the pressure generator 300 and the patient's airway. According to some exemplary embodiments, such active control is achieved by an algorithm that controls the device, for example, by adjusting the speed of the fan 302, according to the implementation example described later. The controller 500 is operably connected to a plurality of sensors 502 that measure various aspects of the system 200, the patient 600, and the surrounding environment. The sensors 502 may include, for example, a pressure sensor that monitors the air pressure in any of the pressure generator (e.g., the flow meter 304 described above), the conduit 400, the outlet 404, or the exhaust port 406. The sensors 502 may include, but are not limited to, a temperature sensor, an ambient pressure sensor, a gauge pressure sensor, a patient flow sensor, an ambient humidity sensor, a microphone, and an accelerometer. External sensors can also be used to directly measure patients, for example, and include, but are not limited to, respiratory belts, non-contact Doppler radar, blood pressure sensors, pulse sensors, and pulse oximeter sensors.

[0042] The pressure generator 300 supplies pressure via the conduit 400 and outlet 404 during the inhalation and exhalation phases of the patient's respiratory cycle. However, as will be further described later, the direction of the airflow through the conduit 400, outlet 404, and exhaust port 406 changes depending on the pressure supplied by the pressure generator 300.

[0043] It is well known and understood that all masks used in positive airway pressure systems have some dead volume between the patient and the exhaust port, which fills with residual exhaled gas at the end of exhalation. Therefore, the air in this dead volume becomes the first air rebreathed during the next inhalation. As used here, this "dead volume rebreathing" is unavoidable because the location of the dead volume (i.e., between the patient and the exhaust port) prevents it from being expelled through the exhaust port while the patient is exhaling. Naturally, the mask does not typically produce a perfect seal on the patient's face, and some of this dead volume is refilled by unintentional leaks. Furthermore, masks can be designed with mechanisms such as multiple small openings or intentionally incomplete seals, which provide intentional leaks and help further mitigate some of this dead volume rebreathing. While these leaks (intentional and unintentional) may help somewhat in reducing dead volume rebreathing, they do little to remove the patient's exhaled air passing through the exhaust port.

[0044] As the patient's exhaled air passes through the exhaust port, other types of rebreathing (referred to here as "circuit rebreathing") may occur depending on the pressurized air supplied by the pressure generator 300 and the patient's exhaled air at the exhaust port 406. Generally, three different scenarios exist, which result in different interactions between the pressurized air supplied by the pressure generator 300 and the patient's exhaled air at the exhaust port 406, as shown in Figures 2 to 4. In particular, it has been found that although there is some turbulent mixing of gases flowing through the circuit, the flow moves mostly in a bolus-like manner, so the exhaled gases do not substantially mix with the fresh air in the conduit.

[0045] As shown in Figure 2, in the first scenario, both the circuit airflow 810 and the patient's expiratory airflow 830 exit through the exhaust port 406 as a combined exhaust flow 840. In other words, the patient's expiratory airflow 830 does not exceed the maximum exhaust flow rate through the exhaust port 406. In this scenario, circuit rebreathing does not occur and exhaled CO2 is prevented from remaining in the circuit because the circuit airflow 810 passes through the entire conduit 400 and exits through the exhaust port 406.

[0046] In contrast, as shown in Figure 3, in the second scenario, the patient's expiratory airflow 830 slightly exceeds the maximum exhaust flow rate through the exhaust port 406, so the entire exhaust flow 840 consists of the patient's exhaled air. The excess patient's expiratory airflow 830 flows back into the conduit 400. However, in this scenario, the backflow is small enough that the entire volume of the patient's exhaled air passing through the conduit 400 is expelled from the exhaust port 406 before the start of the next inhalation, and the patient's expiratory airflow 830 approaches zero near the end of the expiratory phase, so circuit rebreathing still does not occur. In particular, if the patient's expiratory airflow 830 flows back into the conduit 400 due to the bolus airflow described above, the direction of the circuit airflow 810 also reverses as it passes through the conduit 400 and returns to the pressure generator 300. Here again, it is understood that the exhaled gas does not substantially mix with fresh air in the conduit.

[0047] As shown in Figure 4, in the third scenario, the patient's expiratory airflow 830 significantly exceeds the maximum exhaust flow rate through the exhaust port 406. Here again, the entirety of the exhaust flow 840 consists of the patient's exhaled breath, but due to significant backflow, the entire volume of the patient's exhaled breath passing through the conduit 400 cannot be expelled from the exhaust port 406 before the next inhalation, thus causing circuit rebreathing. Specifically, referring to Figure 4B, immediately after the start of inhalation, the direction of the airflow through the conduit 400 and the patient 600 reverses. The exhaust airflow 840 is still entirely composed of the patient's previous exhalation. Due to the large amount of backflow that occurred during the previous exhalation (shown in Figure 4), there is a sufficiently large amount of excess exhaled breath contained inside the conduit 400 at the start of inhalation, so at least a portion of the remaining exhaled breath is inhaled by the patient through at least the initial part of the inhalation.

[0048] In particular, as shown in Figure 4B, immediately after the start of inhalation, the inhaled airflow 820 contains a high level of CO2. However, this is true in all the scenarios shown in Figures 2-4, and also in normal breathing. As shown in Figure 1, only after the patient's airway has been partially cleared of exhaled air does the inhaled airflow 820 contain fresh air to be received by the patient's lungs 606. In the third scenario shown in Figures 4 and 4B, not only does the patient's airway need to be cleared in order to receive fresh air, but any previously exhaled air remaining inside the conduit 400 (exceeding the amount that can be expelled from the exhaust port 406) will be inhaled before the fresh air is received by the patient's lungs 606.

[0049] In short, backflow occurs when the patient's expiratory airflow 830 is greater than the maximum exhaust flow rate through the exhaust port 406, causing the patient's exhaust airflow to flow back into the circuit and return to the pressure generator 300. Circuit rebreathing occurs when the backflow gas flow rate of the patient's exhaled air exceeding the exhaust port 406 is too large to be expelled from the exhaust port 406 before the next inhalation. Therefore, the amount or severity of rebreathing correlates with the amount of patient's exhaled air contained in the circuit at the start of the next inhalation.

[0050] Theoretically, a fourth scenario exists in which the patient's expiratory flow rate is so high that it not only passes through the circuit but also flows into the pressure generator 300 itself, typically exiting the orifice through which the pressure generator 300 draws in air from the environment. This theoretically has the effect of limiting the amount of backflowing expiratory air to the volume of the conduit 400 and the pressure generator 300. However, given the typical volumes within the conduit 400 and the pressure generator 300, this scenario is unlikely to occur. Furthermore, since this would fill the entire circuit with the patient's exhaled air, this fourth scenario can be considered the most likely example of the third scenario shown in Figure 4.

[0051] Since the flow through the conduit 400 is a result of the pressure supplied by the pressure generator 300, it should be understood that the above scenarios can also be discussed in terms of pressure, not just airflow. In the first scenario shown in Figure 2, the pressure generator 300 generates a pressure inside the conduit 400 before the exhaust port 406 that is greater than or equal to the pressure supplied by the patient's lungs 606. Therefore, none of the patient's exhaled air can pass back through the conduit 400. In the second scenario shown in Figure 3, and to some extent in the third scenario shown in Figure 4, the pressure generator 300 generates a pressure inside the conduit 400 before the exhaust port 406 that is less than the pressure supplied by the patient's lungs 606, so the patient's exhaled air can pass back through the conduit 400. In certain cases, the patient's exhaled airflow 830 may be exactly equal to the maximum amount of air that can be expelled from the exhaust port 406. Therefore, the circuit airflow 810 becomes zero, but pressure still exists inside the conduit 400 before the exhaust port 406.

[0052] Similarly, it should be understood that the above scenarios can also be discussed in terms of volume, not just airflow. In the first scenario shown in Figure 2, the amount of air leaving the exhaust port 406 during the patient's entire expiratory period is greater than or equal to the total volume of the patient's exhaled breath. Therefore, none of the patient's exhaled breath can pass back through the conduit 400. Similarly, in the second scenario shown in Figure 3, there is some backflow, but the amount of air leaving the exhaust port 406 during the patient's entire expiratory period is greater than or equal to the total volume of the patient's exhaled breath. Since the total amount of air leaving the exhaust port 406 during the patient's entire expiratory period exceeds the patient's exhaled breath, the total amount of backflow is expelled before inhalation begins. However, in the third scenario shown in Figure 4, the amount of air leaving the exhaust port 406 during the patient's entire expiratory period is less than the total volume of the patient's exhaled breath, so the patient's exhaled breath passing back through the conduit 400 is not completely removed before inhalation begins.

[0053] In dead volume rebreathing, dead volume is finite, and the amount of gas rebreathed is also limited. Patients experiencing lower oxygen intake due to dead volume rebreathing may automatically increase their tidal volume to effectively mitigate the adverse effects of rebreathing. However, as illustrated in the third scenario shown in Figure 4, if the patient has experienced circuit rebreathing, the same response of increasing tidal volume will only worsen the problem. This is because the larger associated expiratory volume will cause greater backflow, resulting in greater rebreathing. This is a vicious cycle that, if allowed to continue, makes CPAP use extremely uncomfortable and potentially dangerous.

[0054] Naturally, in patients of normal size, the risk of circuit rebreathing typically exists in the low pressure range, such as when the exhalation flow rate is relatively low, e.g., 4-6 cmH2O. However, in the case of many patients using APAP (automatic titration CPAP) with extremely low starting pressure limits, the pressure starts at the lower limit of that range and settles when occlusive events are sufficiently ruled out. If the pressure is set as low as possible at the start of treatment, the risk of rebreathing is extremely high. Potentially, many patients in this situation experience rebreathing every night. In addition to the harmful physiological effects of CO2 rebreathing mentioned above, the discomfort associated with rebreathing causes many of these patients to abandon treatment that they probably desperately need.

[0055] Leakage in the mask (or any part of the circuit between the patient and the exhaust port) obviously cannot address the circuit rebreathing described above, but one possible solution to circuit rebreathing is to simply increase the maximum allowable flow rate through the exhaust port and / or intentionally allow more leakage in the part of the circuit between the pressure generator and the exhaust port. However, if the CPAP device is physically modified to ensure that the rebreathing phenomenon is not possible, then excessive exhaust flow rates will occur when high pressure is required (e.g., to address an obstructive event). This can lead to another problem that makes adherence difficult. One such problem is that high flow rates are extremely noisy and can disrupt the sleep of both the patient and the bed partner. Similarly, the impact of high flow rate air on the patient or bed partner can also disrupt sleep. Furthermore, high flow rates can rapidly deplete the liquid reservoir for humidification, potentially depriving the patient of the benefits of humidification throughout the night.

[0056] From the perspective of the above-mentioned problems, the present invention relates to a method for reducing CO2 rebreathing caused by positive airway pressure machines.

[0057] Referring now to Figure 7, in one exemplary implementation of the present invention, in step S100, an airway positive pressure machine (e.g., the airway positive pressure system 200 shown in Figures 1 to 4) is prepared and a mask (e.g., the mask 700 shown in Figure 5) is placed over the patient's face.

[0058] Next, in step S200, pressure is supplied into the patient's airway via the conduit 400 and mask 700 over a treatment period that includes multiple inhalation periods (e.g., shown in Figure 1) and multiple exhalation periods (e.g., shown in the scenarios in Figures 2-4). In the most basic application of positive airway pressure therapy, continuous pressure is applied during both the inhalation and exhalation periods, which is commonly referred to as continuous positive airway pressure (CPAP). In another known application, two different pressures are supplied (BPAP). In one exemplary implementation of the present invention, referring hereto to Figure 8, the use of the positive airway pressure system 200 of the present invention provides a pressure profile 1100 throughout the patient's respiratory cycle, comprising a relaxation positive airway pressure (RPAP) 1150 applied during a portion of the patient's inhalation period 1110, including the end of the patient's inhalation period 1112 (i.e., the start of the next exhalation period 1120), and a therapeutic positive airway pressure (TPAP) 1130 applied during a portion of the exhalation period 1120, including the end of the exhalation period 1122 (i.e., the start of the next inhalation period 1110). U.S. Patent Application No. 18 / 536800 (filed December 12, 2023, titled "POSITIVE AIRWAY PRESSURE SYSTEMS AND METHODS FOR TREATING SLEEP DISORDERED BREATHING") provides an additional description of the pressure profiles that can be provided by the positive airway pressure system 200 of the present invention, which is incorporated herein by reference.

[0059] During the treatment period, at step S300, one or more parameters relating to the patient and / or the positive airway pressure machine are monitored periodically, and at step S400, it is determined whether the patient is experiencing excessive CO2 rebreathing. For example, as mentioned above, since a certain amount of rebreathing is expected from dead-end volume rebreathing, even a small amount of circuit rebreathing may be acceptable. In contrast, "excessive CO2 rebreathing" as used here means an increase in CO2 above ambient CO2 levels, which has negative physiological effects on the patient. There is a direct relationship between the presence of dissolved CO2 and pH; that is, increased CO2 concentration leads to a decrease in pH in the blood and tissues. Impacts on performance, particularly on cognitive diversity, can appear even with a slight increase in CO2 concentration above normal levels. For reference, normal air has a CO2 concentration of approximately 0.04% (400 ppm, or about 0.3 mmHg at sea level), while arterial blood CO2 (PaCO2) ranges from 35 to 45 mmHg (46,000 ppm to 59,000 ppm). The following (Table 1), quoted from the Wisconsin Department of Health Services (https: / / www.dhs.wisconsin.gov / chemical / carbondioxide.htm), shows the various effects of routine daily exposure on changing CO2 exposure levels. In particular, a CO2 concentration of 5,000 ppm is also the 8-hour weighted limit set by OSHA (Occupational Safety and Health Administration).

[0060] [Table 1]

[0061] The current standard for the design of medical device masks for sleep apnea syndrome (ISO 17510:2015 - Medical devices - Respiratory therapy for sleep apnea syndrome - Masks and their application accessories) requires a maximum recommended time-weighted average of 1% inhaled CO2 concentration (10,000 ppm). Therefore, in some exemplary implementations, "excessive CO2 rebreathing" is defined as rebreathing that results in 1% inhaled CO2.

[0062] However, as this ISO standard states, "A 1% inhaled CO2 fraction is represented by adding 1013.25 Pa (7.6 torr) to the test model in Annex F, resulting in an end-exhaled CO2 value of 1013.25 Pa (7.6 torr) + 5066.25 Pa (38 torr) or 6079.5 Pa (45.6 torr) in the test. This represents a 20% increase in CO2 levels. Based on this, the Committee selected a 20% increase in the normal state limit for CO2 levels. Similarly, a 60% increase in the single abnormal state limit for CO2 levels represents a time-weighted average for 3% inhaled CO2."

[0063] In other words, current ISO mask design guidelines allow 10,000 ppm (i.e., 1%) for nocturnal exposure, which is twice the workplace tolerance limit shown in Table 1. Furthermore, the ISO 17510 test conditions recommend a patient with a respiratory rate of 15 brpm, a tidal volume of 500 mL, and an I:E ratio of 1:2. This problem can worsen if the patient breathes with a larger tidal volume, a faster respiratory rate, or a more equal I:E ratio. Therefore, in some exemplary implementations, "excessive CO2 rebreathing" includes rebreathing that results in approximately 0.5% (5000 ppm), 0.4% (4000 ppm), 0.3% (3000 ppm), 0.2% (2000 ppm), or 0.1% (1000 ppm) of inhaled CO2. In some specific implementations, "excessive CO2 rebreathing" includes rebreathing that results in approximately 0.09% (900 ppm), 0.08% (800 ppm), 0.07% (700 ppm), 0.06% (600 ppm), or 0.05% (500 ppm) of inhaled CO2. In one exemplary implementation, "excessive CO2 rebreathing" includes any amount of inhaled CO2 that exceeds the CO2 levels in the ambient air.

[0064] Regardless of the level of CO2 inhalation considered to be excessive CO2 rebreathing, referring to Figure 7, if it is determined that the patient is not experiencing excessive CO2 rebreathing, the pressure profile applied in step S200 is permitted to continue. However, if excessive CO2 rebreathing is determined to be present, the pressure profile is adjusted in step S500 to reduce CO2 rebreathing, and / or the positive airway pressure system is adjusted in step S600 to reduce CO2 rebreathing.

[0065] Since directly measuring the level of inhaled CO2 may be difficult or impossible depending on the specific system, in relation to step S300, various different parameters that correlate with the level of inhaled CO2 may be monitored.

[0066] According to several exemplary implementations, one or more parameters monitored include patient expiratory volume. Furthermore, according to several exemplary implementations, patient expiratory volume can be estimated based on one or more physiological parameters, including, but not limited to, patient height, patient weight, patient BMI, patient sex, patient age, measured respiratory rate, measured I:E ratio, measured tidal volume, measured minute ventilation, measured expiratory pressure produced by the patient's lungs, measured expiratory flow rate produced by the patient's lungs, and measured peak expiratory flow rate. The measured value can be determined based on a single measurement, or, in some preferred embodiments, based on multiple measured values ​​over time, such as a rolling average.

[0067] In some exemplary implementations, referring again to Figures 2–4, one or more parameters monitored include the patient's exhaled air flowing back into the conduit during the exhalation period. This quantifiable quantity can be determined directly by measuring the flow rate through the conduit 400, or by comparing it with one or more other measured values. For example, this quantity can be estimated by comparing the patient's exhaled airflow rate 830 with the known maximum flow rate that can be discharged from the exhaust port 406.

[0068] The majority of the patient's exhaled air should exit through the exhaust port 406. As used here, “majority” means at least 90%. In some exemplary implementations, “majority” means at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99%.

[0069] The sensors 502 described above, as shown in Figures 1 to 4, can be used to measure one or more parameters. For example, a flow meter positioned on or near the conduit 400 and mask 700 can measure the individual circuit airflow rate 810 and patient exhalation flow rate 830. The specific sensors used and their arrangement will be readily understood by those skilled in the art to enable the measurement of the parameters described above.

[0070] Regardless of the specific parameters and measurement methods used, the objective is to determine whether the patient's exhaled air is present in the conduit at the start of each inhalation period. Conveniently, due to the bolus airflow through the aforementioned conduit, this determination can be made without considering the mixing of exhaled gas and fresh gas.

[0071] In some exemplary implementations, if no patient exhaled air is present in the conduit 400 at step S400, i.e., in the scenarios shown in Figures 2 and 3, it is determined that the patient has not experienced excessive CO2 rebreathing. Naturally, even if the expiratory flow rate 830 is less than the exhaled flow rate 840, a small amount of patient exhaled air may flow backward into the conduit 400 due to a simple mixing of the expiratory flow rate 830 and the circuit flow rate 810. This small amount of exhaled air has a negligible effect on the patient and is therefore easily ignored.

[0072] According to one exemplary implementation, in step S500, the pressure profile applied by the positive airway pressure system is adjusted to reduce CO2 respiration. Specifically, the pressure supplied by the pressure generator 300 is adjusted so that the majority of the patient's exhaled air is expelled through the exhaust port 406. Similarly, the pressure supplied by the pressure generator 300 is adjusted so that the amount of air leaving the exhaust port is greater than or equal to the patient's exhaled air volume.

[0073] For example, in some exemplary implementations, if it is determined that the patient is experiencing excessive CO2 rebreathing, the pressure supplied by the pressure generator 300 is increased until the patient no longer experiences excessive CO2 rebreathing.

[0074] In some exemplary implementations, the pressure increases only at the end of the exhalation period to remove patient exhaled air from the conduit 400 through the exhaust port 406.

[0075] Preferably, to avoid circuit rebreathing, the patient's exhaled air is removed from the conduit before the start of the next inhalation period. However, in some implementations, it is assumed that at least a portion of the patient's exhaled air is still present in the conduit 400 at the start of the next inhalation period. In these implementations, the pressure supplied by the pressure generator 300 is maintained or raised to an elevated level until the patient's exhaled air is removed from the conduit 400 through the exhaust port 406. However, it is preferable that the patient does not experience excessive CO2 rebreathing during the start of the next inhalation period.

[0076] In all cases, once the patient's exhaled air is removed from the conduit 400, the pressure decreases in some embodiments.

[0077] The specific methods for increasing and decreasing the pressure are not limited. In some embodiments, the pressure may be increased as soon as it is determined that circuit rebreathing is occurring, for example, as soon as it is determined that a sufficient amount of the patient's exhaled air has flowed back into the conduit 400. In some other embodiments, the pressure is increased during the next exhalation period, so that the patient may experience one respiration with excessive CO2, but will not experience any further excessive CO2 rebreathing. In yet another embodiment, the pressure is gradually increased over two or more exhalation periods. This may result in slightly more CO2 rebreathing, but the gradual increase in pressure will not be as noticeable to the patient.

[0078] Furthermore, a safety factor may be applied to prevent accidental CO2 rebreathing due to variations in the patient's respiration. In particular, the moving average of the patient's expiratory volume can be calculated using a pressure adjusted so that the exhalation volume is equal to the average patient expiratory volume plus the safety factor. In some embodiments, this safety factor is approximately 20%, while in other embodiments, it is approximately 15%, 10%, or 5%. This may result in a pressure slightly higher than necessary to prevent excessive CO2 rebreathing, but it is thought that this will lead to a more consistent pressure application over time, ultimately increasing patient comfort.

[0079] Furthermore, according to some exemplary implementations of the present invention, the pressure supplied by the pressure generator 300 can account for intentional or unintended leaks. If there is backflow of patient exhalation, it is removed through the exhalation valve via intentional or unintended leaks in the mask and is not a problem as long as there is no leak at the start of the next inhalation. For example, in systems using a full-face mask, it is well known that patients with beards experience a higher level of leaks than patients with little or no facial hair. However, the specific level of unintended leaks varies from patient to patient, or in some cases, depending on the night. Therefore, in some implementations of the present invention, unintended leaks are measured and the pressure supplied by the pressure generator 300 is reduced accordingly. In other words, the exhaust flow is not necessarily limited to the flow through the exhaust port 406 shown in Figures 1 to 4, but may include any leaks, whether intentional or unintended.

[0080] According to one exemplary implementation, in step S600, the positive airway pressure system is physically adjusted to reduce CO2 rebreathing. In some exemplary implementations, the exhaust assembly and / or mask of the positive airway pressure system can be replaced with an alternative version that provides a predetermined maximum exhaust flow rate. In one other exemplary implementation, referring again to Figures 5-6, the insert 730 contained within the secondary outlet 726 of the exhaust assembly 720 can be replaced with one of several interchangeable ports that each provide a different predetermined maximum exhaust flow rate from the secondary outlet 726. While these particular methods of adjusting the positive airway pressure system cannot be easily performed immediately or dynamically during the course of treatment, adjusting the positive airway pressure system in this manner provides overall adjustment of the machine. In some exemplary implementations, the positive airway pressure system is expected to provide feedback to the user regarding what adjustments are needed. For example, the system may indicate to the user which specific interchangeable port is needed to further reduce CO2 rebreathing.

[0081] In some other exemplary embodiments, the exhaust assembly has an adjustable exhaust port. For example, although not explicitly shown, the exhaust port may define an exhaust orifice with an adjustable size that can be physically changed. Several means of adjusting the size of the exhaust orifice are well known in the art and can be readily incorporated into the exhaust assembly of the present invention or provide non-limiting examples, in certain embodiments two plates, each defining one or more holes, are rotatable relative to each other, allowing for selective positioning of the holes to adjust the entire orifice defined by the exhaust orifice. In some exemplary implementations, the positive airway pressure system includes a mechanism for actively controlling the adjustable exhaust port.

[0082] Referring again to Figure 8, as previously mentioned, in one exemplary implementation of the present invention, the use of the positive airway pressure system 200 of the present invention results in a pressure profile 1100 that includes a relaxation positive airway pressure (RPAP) 1150 applied during a portion of the patient's inhalation period 1110, including the end of the patient's inhalation period 1112 (i.e., the start of the next exhalation period 1120), and a therapeutic positive airway pressure (TPAP) 1130 applied during a portion of the exhalation period 1120, including the end of the exhalation period 1122 (i.e., the start of the next inhalation period 110). As shown in Figure 8, the TPAP 1130 is greater than the RPAP 1150. Furthermore, the pressure decreases from TPAP 1130 to RPAP 1150 via a relaxation transition (RT) 1140 that occurs in the initial part of the inhalation period 1110 (i.e., after the end of the exhalation period 1120). Similarly, pressure increases from RPAP 1150 to TPAP 1130 via a therapeutic transition (TT) 1160 that occurs midway through the expiratory period 1120.

[0083] According to some exemplary implementations of the present invention, the positive pressure breathing system 200 provides a pressure profile 1100 as shown in Figure 8, and if it is determined in step S400 that the patient is experiencing excessive CO2 rebreathing, the RPAP 1150 is increased in step S500. By increasing the pressure during RPAP 1150, the portion of RPAP 1150 that occurs particularly during the expiratory period 1120 helps to remove the patient's exhaled air from the conduit before the next inhalation period.

[0084] Similarly, in another exemplary implementation, if it is determined in step S400 that the patient is experiencing excessive CO2 rebreathing, TPAP1130 is increased in step S500. By increasing the pressure during TPAP1130, the portion of TPAP1130 that occurs particularly during the expiratory period 1120 helps to remove the patient's exhaled air from the conduit before the next inhalation period.

[0085] In another exemplary implementation, the timing of TT and / or RT is adjusted, rather than the level of pressure being supplied.

[0086] In some exemplary implementations, if it is determined in step S400 that the patient is experiencing excessive CO2 rebreathing, the timing of TT1160 is adjusted in step S500 to occur earlier during expiratory period 1120. This allows a higher TPAP1130 to be maintained over a larger portion of expiratory period 1120, which helps to clear the patient's exhalation conduit.

[0087] In some exemplary implementations, if it is determined in step S400 that the patient is experiencing excessive CO2 rebreathing, the timing of RT1140 is adjusted in step S500 to occur in the latter half of the inhalation period 1110. Thus, a higher TPAP 1130 is maintained until the patient's exhaled air is removed from the conduit 400 via the exhaust port 406, while at least a portion of the patient's exhaled air still remains in the conduit 400 at the beginning of the next inhalation period.

[0088] The pressure profile adjustments described above are merely examples, and it should be understood that these can be used individually or in combination.

[0089] Figure 8 shows only two respiratory cycles, an inhalation period 1110 and an expiratory period 1120. This is merely illustrative, and it should be understood that the method described above is performed over periods including multiple inhalation and expiratory periods. Furthermore, while the pressure profile 1100 shown in Figure 8 is repeated in the same way between each respiratory cycle of the inhalation period 1110 and the expiratory period 1120, in some exemplary implementations, one or more of TPAP 1130, RT 1140, RPAP 1150, and TT 1160 may vary between respiratory cycles. Some of these potential variations have been described above, but additional details regarding the pressure profiles that can be provided by the positive airway pressure system 200 of the present invention can be found in U.S. Patent Application No. 18 / 536800. The adjustments made to the pressure profile in step S500 described above can be performed individually or in combination with each of the various embodiments described in U.S. Patent Application No. 18 / 536800 with respect to TPAP, RT, RPAP, and / or TT.

[0090] For example, referring to Figure 9, in some exemplary implementations, the relaxation transition can be performed in multiple steps to further enhance comfort. As shown in Figure 9, similar to the implementation shown in Figure 8, in the pressure profile 2100 of this exemplary implementation, the pressure decreases from TPAP 2130 to RPAP 2150, starting immediately after the start of the inhalation period 2110 and continuing through RT 2140, which is still present during the early part of the inhalation period 2110. Similarly, the pressure increases from RPAP 2150 to TPAP 2130, continuing through TT 2160, which occurs midway through the exhalation period 2120. However, unlike the implementation shown in Figure 8, in Figure 9, during RT 2140, there is an initial pressure decrease during the first period 2142, followed by a subsequent pressure decrease during the second period 2144.

[0091] During the first period 2142, the pressure delivered into the patient's airway decreases by an initial amount from TPAP 2130 and is maintained substantially constant at an intermediate pressure 2155, which is lower than TPAP 2130 but higher than RPAP 2150. In this exemplary implementation shown in Figure 9, the first period 2142 ends when the patient's airflow reaches the peak inhalation flow rate 2114, and the second period 2144 ends when the patient's airflow reaches the peak expiratory flow rate 2124. Thus, the overall period over which RT 2140 occurs in Figure 9 is significantly longer than that of RT 1140 shown in Figure 8. However, in another implementation, the first pressure drop from TPAP 2130 to the intermediate pressure 2155 occurs relatively quickly, and the second pressure drop from the intermediate pressure 2155 to RPAP 2150 occurs after the peak inhalation flow rate 2114. Alternative timings for the first and second pressure drops are also possible without departing from the spirit and scope of the invention. Furthermore, although Figure 9 shows only two pressure drops during RT2140, it is conceivable that three or more pressure drops may occur without departing from the spirit and scope of the present invention.

[0092] The TPAP2130, RT2140, RPAP2150, and TT2160 parameters of the pressure profile 2100 shown in Figure 8 can be modified in the same manner as TPAP1130, RT1140, RPAP1150, and TT1160 described above, with reference to Figure 8.

[0093] However, according to some exemplary implementations of the present invention, in which the positive pressure breathing system 200 provides the pressure profile 2100 shown in Figure 9, in step S400, if it is determined that the patient is experiencing excessive CO2 rebreathing, then in step S500, multiple pressure drops can also be individually modified during RT2140. For example, the first pressure drop may still occur, but if it is determined that the patient is experiencing excessive CO2 rebreathing, one or more subsequent pressure drops may be eliminated. This results in an overall increase in RPAP2150, which helps to remove the patient's exhaled air from the conduit before the next inhalation period, as described above.

[0094] Furthermore, it should be understood that the methods described above can be adjusted depending on whether the patient is awake, asleep, or in an intermediate state. Generally, comfort takes precedence while the patient is awake, and treatment takes precedence while the patient is asleep. While the patient is awake, i.e., when comfort takes precedence, it is important to maintain low pressure during the exhalation phase and to maintain low pressure for as long as possible. However, sufficient pressure should be maintained to remove the patient's exhaled air from the conduit before the next inhalation phase. Once the patient falls asleep, the required level of comfort only needs to be maintained to the extent that the patient does not wake from sleep, and therefore the pressure can be increased.

[0095] Accordingly, in some exemplary embodiments, the positive pressure breathing system 200 can determine whether the patient is awake or asleep and modify one or more parameters of the pressure profile accordingly. For example, the pressure may be reduced to a minimum while the patient is awake or in a light sleep state, and then gradually increased over a ramp period as the patient falls asleep, reaches deeper sleep, and / or sleeps for a longer period. For example, in some exemplary implementations, the pressure increasing process includes gradually increasing the pressure supplied at the end of the expiratory period over consecutive expiratory periods (e.g., the TPAP 1130 shown in Figure 8 increases).

[0096] In some exemplary implementations, the pressure-increasing process involves gradually lengthening the period during which higher pressure is supplied at the end of the expiratory period over consecutive expiratory periods (for example, TT1160 occurring earlier during expiratory period 1120 as shown in Figure 8). By initiating TT1160 earlier during expiratory period 1120, more time is provided for the gradual transition from RPAP1150 to TPAP1130 while providing the pressure necessary over time to remove the patient's exhaled air from the conduit before the next inhalation period. Means for determining whether the patient is awake or asleep include, but are not limited to, the detection of rapid eye movements (REM), the detection of flow restriction or increased upper airway resistance, the detection of responses to central sleep apnea, and monitoring of changes in respiratory parameters (e.g., respiratory rate, tidal volume, peak flow, etc.), as breathing generally becomes regular once the patient falls asleep. The measurements used to determine whether a patient is awake or asleep can be performed by sensors or mechanisms integrated into the positive airway pressure machine, or they can be provided as separate or external devices configured to transmit data to the positive airway pressure machine.

[0097] Naturally, a patient's respiration is not always stable throughout the night, even if sleep is not interrupted. Therefore, it is important to monitor the patient's exhalation level and adjust the pressure as needed to reduce, and preferably eliminate, circuit rebreathing. For this purpose, in some exemplary implementations, an initial pressure is supplied during the first exhalation period, which is high enough to ensure that the patient's exhalation does not flow back into the conduit. The pressure supplied during subsequent exhalation periods then decreases until a minimum amount of circuit rebreathing occurs. The pressure then increases until the patient's exhalation no longer flows back into the conduit. In some embodiments, the amount by which the pressure decreases during consecutive exhalation periods is set to a predetermined amount, and the final pressure increase is performed at a level below this predetermined amount.

[0098] This pressure adjustment step may be performed continuously throughout the treatment period or repeated periodically throughout the treatment period. In either case, one or more parameters can be monitored using the sensor 502 described above with respect to Figure 1 to determine whether some of the patient's exhaled air is flowing back into the conduit as described above.

[0099] Furthermore, according to several exemplary implementations, the mask's leakage characteristics can be calculated over time by continuously monitoring the parameters described above. These characteristics can be used to compare the actual mask leakage with the expected leakage amount. If the actual mask leakage falls below a minimum threshold, it can indicate that there is a problem with the mask itself, for example, partial blockage of one or more leak ports due to dirt or condensation. Therefore, in some implementations of the present invention, if the calculated mask leakage falls below a minimum threshold, the patient is provided with a warning. In some implementations, feedback is provided that a part of the CPAP device should be changed, such as the leak port, the mask itself, and / or other parts of the circuit. In some situations, it has been recognized that replacing the conduit 400 can improve the rebreathing of the circuit. A smaller tube diameter results in a faster flow rate, allowing the circuit to be cleared more quickly.

[0100] Those skilled in the art will recognize that additional embodiments and implementations are possible without departing from the teachings of the present invention or the scope of the claims below. This detailed description, in particular the specific details of the exemplary embodiments disclosed herein, is provided primarily for clarity of understanding and does not imply any necessary limitations to be understood therefrom. Modifications can be made without departing from the spirit or scope of the claimed invention and will be obvious to those skilled in the art upon reading this disclosure.

Claims

1. CO2 is released from the positive airway pressure machine, which includes a pressure generator, a mask configured to be positioned over the patient's face, a conduit operably connecting the pressure generator to the mask, and an exhaust port. ２ A method to reduce rebreathing, The procedure includes the step of supplying pressure to the patient's airway via a conduit and mask over a treatment period that includes multiple inhalation periods and multiple exhalation periods, The supplied pressure is at a level sufficient to expel most of the patient's exhaled air through the exhaust port, in this manner.

2. During each inhalation period, the patient's CO2 level was less than 0.1%. ２ The method according to claim 1, wherein the person inhales the following.

3. The method according to claim 1, wherein the patient's exhaled breath is not present in the conduit at the start of each inhalation period.

4. The steps include measuring the patient's exhaled air volume, The method according to claim 1, further comprising the step of adjusting the supply pressure so that the majority of the patient's exhaled air is discharged through the exhaust port.

5. A step to determine that during the exhalation period, some of the patient's exhaled air flows into the conduit, The method according to claim 1, further comprising the step of increasing the pressure to remove the patient's exhaled air from the conduit through an exhaust port.

6. The method according to claim 5, wherein the step of increasing pressure includes increasing the pressure supplied at the end of the exhalation period.

7. The method according to claim 5, wherein the step of increasing the pressure includes increasing the time during the exhalation period to which the increased pressure is supplied.

8. The method according to claim 5, further comprising the step of reducing the supply pressure after the patient's exhaled air has been removed from the conduit through the exhaust port.

9. The method according to claim 5, wherein the step of increasing pressure includes increasing the pressure supplied during the beginning portion of the next inhalation period until the patient's exhaled air is removed from the conduit through the exhaust port.

10. The steps include supplying initial pressure during the first exhalation period, wherein the initial pressure is configured to prevent the patient's exhaled air from entering the conduit; The steps include reducing the pressure supplied during a continuous exhalation period by a predetermined amount until some of the patient's exhaled air enters the conduit, The method according to claim 1, further comprising the step of increasing the pressure to a final pressure if the patient's exhaled air does not enter the conduit.

11. The steps include receiving data from one or more sensors that measure pressure or flow rate through a conduit, The method according to claim 1, further comprising the step of determining whether a portion of the patient's exhaled breath enters the conduit.

12. Steps to determine whether the patient is awake or asleep, If the patient is awake, the step is to supply minimum pressure, The method according to claim 1, further comprising the step of increasing the pressure supplied over a certain lamp period after the patient has fallen asleep.

13. The method according to claim 12, wherein the minimum pressure is sufficient to ensure that no patient exhaled air is present in the conduit at the start of the inhalation period.

14. The method according to claim 12, wherein, during the step of increasing the pressure, the pressure supplied at the end of each exhalation period is gradually increased over a continuous exhalation period.

15. The supplied pressure increases during each exhalation period, reaching a higher pressure some time before the next inhalation period. The method according to claim 12, wherein during the step of increasing the pressure, the higher pressure is gradually reduced over a period of continuous exhalation.

16. The supplied pressure increases during each exhalation period, reaching a higher pressure some time before the next inhalation period. The method according to claim 12, wherein, during the step of increasing the pressure, the period is gradually increased over a continuous exhalation period.

17. The pressure is relaxed positive airway pressure during a portion of the inhalation period, including the end of the inhalation period. The pressure is therapeutic positive airway pressure during a portion of the expiratory period, including the end of the expiratory period, and such therapeutic positive airway pressure is greater than the relaxing positive airway pressure. The method according to claim 1, wherein after the end of the expiratory period, the pressure is reduced from therapeutic positive airway pressure to palliative positive airway pressure.

18. A step to determine if some of the patient's exhaled air enters the conduit during the exhalation period, The method according to claim 17, further comprising the step of increasing palliative positive airway pressure.

19. A step to determine if some of the patient's exhaled air enters the conduit during the exhalation period, The method according to claim 17, further comprising the step of maintaining therapeutic positive airway pressure over a larger portion of the expiratory period.

20. A step to determine if some of the patient's exhaled air enters the conduit during the exhalation period, The method according to claim 17, further comprising the step of increasing therapeutic positive airway pressure.

21. The method according to claim 1, further comprising the step of changing the exhaust port to adjust the maximum exhaust flow rate from the exhaust port.

22. The step of changing the exhaust port includes replacing the exhaust port with one of several interchangeable ports. The method according to claim 21, wherein each of the interchangeable ports has a predetermined exhaust flow rate.

23. The exhaust port includes an exhaust orifice with an adjustable size. The method according to claim 21, wherein the step of modifying the exhaust port includes changing the size of the exhaust orifice.

24. The method according to claim 21, further comprising the step of providing feedback to the user regarding what modifications to the exhaust port may be necessary.

25. CO2 is released from the positive airway pressure machine, which includes a pressure generator, a mask configured to be positioned over the patient's face, a conduit operably connecting the pressure generator to the mask, and an exhaust port. ２ A method to reduce rebreathing, A step of supplying pressure to the patient's airway via a conduit and mask over a treatment period including multiple inhalation and multiple exhalation periods, The steps include measuring the patient's exhaled air volume, A method comprising the step of adjusting the pressure supplied at the end of the exhalation phase so that the patient's exhaled air is not present in the conduit at the start of the inhalation phase.

26. CO2 is released from the positive airway pressure machine, which includes a pressure generator, a mask configured to be positioned over the patient's face, a conduit operably connecting the pressure generator to the mask, and an exhaust port. ２ A method to reduce rebreathing, The steps include measuring the patient's exhaled air volume, A step of supplying pressure into the patient's airway via a conduit and mask over a therapeutic period including multiple inhalation and multiple exhalation periods, wherein the pressure is supplied at an initial pressure configured to prevent the patient's exhaled air from entering the conduit; The steps include reducing the pressure supplied during a continuous exhalation period by a predetermined amount until some of the patient's exhaled air enters the conduit, A method comprising the step of increasing the pressure to a final pressure if the patient's exhaled air does not enter the conduit.

Images