Positive airway pressure systems and methods for treating sleep-disordered breathing

Abstract

Treatment for sleep-disordered breathing involves supplying pressure to the patient's airways over a period including multiple inhalation and exhalation periods. The pressure is a relaxing positive airway pressure during a portion of the inhalation period, including the end of the inhalation period, and a therapeutic positive airway pressure greater than the relaxing positive airway pressure during a portion of the exhalation period, including the end of the exhalation period. After the end of the exhalation period, the pressure decreases from the therapeutic positive airway pressure to the relaxing positive airway pressure.

Description

Technical Field

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

Background Art

[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, in the systems and methods of the present invention, the pressure supplied into the patient's airway is intentionally decreased from a therapeutic airway positive pressure to a relief airway positive pressure after the end of the exhalation period and maintained at a lower pressure through the inhalation period and the next exhalation period.

[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 30 and 70 years old have sleep apnea, and the figure 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 mask or nasal pillow mask to increase air pressure in the patient's throat, preventing airway obstruction. As shown in Figure 2, the CPAP machine delivers continuous pressure during both inhalation and exhalation. CPAP also increases the functional residual capacity of the lungs and stretches and hardens the pharyngeal airway. The pressure delivered during CPAP treatment varies depending on the patient, but the generally accepted theory is that a minimum pressure is required to keep the patient's airway open during the inhalation period and allow airflow into the patient's respiratory system. While CPAP therapy is effective in treating sleep apnea, the airflow and pressure delivered through the mask often cause discomfort, leading to discontinuous use by patients.

[0005] Referring to Figure 3, next-generation positive airway pressure (BPAP) therapy is designed to reduce pressure at the start of the expiratory phase (typically 5-10 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. The driving principle of BPAP therapy was the need to maintain therapeutic pressure levels during inspiration when the airway is obstructed. It was generally supported that as long as the pressure was maintained during inspiration, an equivalent pressure was not needed during expiration for therapeutic purposes. Therefore, BPAP machines reduce the pressure during the expiratory phase (EPAP) but maintain the inspiratory pressure (IPAP). This idea led to the theory that maintaining pressure during the inspiratory phase is crucial. In fact, it was generally supported that EPAP "widens the airway," while IPAP "blows the airway." Historically, this idea likely stemmed from the proliferation of biphasic therapy, leading engineers to believe that IPAP absolutely had to be maintained, while EPAP could be sacrificed as needed to improve comfort.

[0006] Referring to Figure 4, several modifications have emerged as extensions of the BPAP system in which the exhalation pressure decreases proportionally to the patient's expiratory flow rate, rather than dropping sharply at the start of exhalation. In these systems, the maximum pressure drop is usually smaller than in BPAP, typically limited to 1–3 cmH₂O. Consistent with the idea that pressure should be maintained during the inhalation phase, the inhalation pressure is maintained at the maximum required therapeutic level, including at the end of inhalation, as shown in Figure 4.

[0007] Referring to Figure 5, a passive system has been developed as a lower-cost alternative to the positive airway pressure system. This system uses a check valve to allow the inhaled airflow to flow with very little resistance, and during exhalation, the exhaled airflow passes through a fixed air pressure limiter. As shown in Figure 5, the inhaled pressure is not affected by the device, and the exhaled pressure increases in accordance with the patient's exhaled airflow. More precisely, there is no pressure supplied during inhalation, but due to the design of the device itself, the pressure begins to increase immediately after exhalation.

[0008] Ongoing research into the underlying mechanisms and treatments of sleep-disordered breathing has led to a wide variety of often contradictory conclusions. While the common understanding in the field continues to emphasize the need for higher inhaled positive airway pressure (IPAP), in a 2015 paper ("Expiratory and inspiratory positive airway pressures in objective sleep apnea: how much pressure is necessary? A different point of view," published in Volume 2, Issue 6 of the Journal of Lung, Pulmonary & Respiratory Research), the authors proposed the use of a physical device that increases resistance and pressure during exhalation but does not affect inhaled pressure, similar to the passive device discussed with respect to Figure 5. As described in this paper, current BPAP machines cannot set EPAP to zero. As reflected in Figure 6, this paper also hypothesizes that independent control of inhaled and expiratory pressure should not be limited to setting IPAP higher than EPAP, but rather that IPAP can be set lower than EPAP (as shown by the triangular line) or even near zero (as shown by the circular line). These "inverted" BPAP machines can be configured to operate like EPAP devices, where pressure changes occur immediately and are maintained constant between individual inhalations and exhalations.

[0009] In another 1993 paper ("Dynamic Upper Airway Imaging during Awake Respiration in Normal Subjects and Patients with Sleep Disordered Breathing," published in Volume 148 of the American Review of Respiratory Disease), the authors found the following regarding awake respiration: (1) In apnea subjects, the upper airway is significantly smaller than in normal subjects, particularly at the anatomical level of the posterior palate and posterior tongue muscles. In apnea patients, the airway has an anterior-posterior configuration, unlike the normal airway which has a horizontal configuration with a long axis in the lateral direction. (2) In all three subject groups, there was little airway narrowing during inhalation, suggesting that the activity of the upper airway dilating muscles balances the effect of negative intracavitary pressure. In apnea patients, the airway is more dilated during early inhalation, likely reflecting increased activity of the upper airway dilating muscles. (3) Positive airway pressure during exhalation leads to airway dilation, which is greatest in patients with sleep apnea, indicating that the airways of patients with sleep apnea are more expandable than normal airways. (4) At the end of exhalation, the upper airway was significantly narrowed, especially in patients with sleep apnea. These findings are specific to awake breathing, and the authors specifically note that they cannot draw conclusions about what happens during sleep or when subjects breathe through their mouths. Nevertheless, the literature hypothesizes that if the same results apply during sleep, the pressure increase near the end of exhalation may prevent a decrease in airway dimensions, as reflected in Figure 7. However, they also warn that pressure during early exhalation is unnecessary and may cause discomfort by creating resistance to the patient's exhalation. It appears that no positive airway pressure system utilizing the concepts proposed in this literature has been developed in the many years since its publication. [Overview of the project] [Problems that the invention aims to solve]

[0010] Despite decades of research and development of a wide range of systems and methods, patient adherence to positive airway pressure therapy remains low due to discomfort. New approaches to treating sleep disorders would be highly desirable and beneficial. [Means for solving the problem]

[0011] (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, in the systems and methods of the present invention, the pressure supplied into the patient's airway is intentionally reduced from therapeutic positive airway pressure to easing positive airway pressure after the end of the expiratory phase and maintained at a lower pressure throughout the inhalation phase and the following expiratory phase.

[0012] Unlike conventional systems and methods where inspiratory positive airway pressure (IPAP) is greater than expiratory positive airway pressure (EPAP), the system and method of the present invention generally results in lower pressure during the inhalation phase compared to the expiratory phase. This has been found to increase patient comfort while providing therapeutic effects similar to conventional CPAP or BPAP devices where IPAP is always greater than or equal to EPAP.

[0013] This invention utilizes the viscoelastic properties of airway tissue by forcing expansion of airway tissue during the latter half of the expiratory phase, maintaining the airway until lung volume increases during the first half of the inhalation phase, and at that point maintaining airway patency without additional pressure support by tracheal traction.

[0014] A smaller airway cross-sectional area results in increased resistance and decreased airflow, increasing the likelihood of obstructive events such as apnea. However, by applying pressure to a patient's airway, force is transmitted to the airway tissue, where it is stored or "charged." It is important to recognize that the amount of "charge" imparted to the tissue depends not only on the magnitude of the force but also on the duration for which the force is applied. Specifically, because tissues have both elastic and viscous responses, a sudden force may produce an elastic response, but this reverses immediately upon removal of the force. In other words, as soon as the force is removed, the tissue elastically returns to its original shape. For a viscoelastic response to occur, where the tissue remains in an expanded shape for a period of time, the force must be applied over a period of time. In other words, once a viscoelastic response occurs, there is a delay after the force is removed before the tissue returns to its narrower shape.

[0015] By concentrating pressure application at the end of the expiratory phase and the beginning of the inhalation phase, it becomes possible to have lower pressure for the remainder of the inhalation phase, resulting in a reduction in mean airway pressure and improved overall patient comfort, which is known to improve adherence to treatment.

[0016] As a result of this new understanding, the pressure profile obtained from the present invention differs from that of previously known positive airway pressure systems. Specifically, unlike all previous systems, according to some exemplary implementations of the present invention, the pressure decreases well before the end of the inhalation period and is maintained at a reduced pressure not only at the start of the expiratory period but also for a period thereafter.

[0017] According to some exemplary implementations of the present invention, a method for treating sleep-disordered breathing includes supplying pressure to a patient's airway over a period comprising multiple inhalation periods and multiple expiratory periods. The pressure is positive relaxation airway pressure (RPAP) during a portion of the inhalation period, including the end of the inhalation period. The pressure is positive therapeutic airway pressure (TPAP) during a portion of the expiratory period, including the end of the expiratory period. TPAP is greater than RPAP, and the pressure decreases from TPAP to RPAP after the end of the expiratory period. The timing of the pressure transition between TPAP and RPAP is not directly related to the timing of the transition between the inhalation and expiratory periods. Rather, the pressure is intentionally decreased from TPAP to RPAP via a relaxation transition (RT) that typically occurs during the early portion of the inhalation period. Similarly, the pressure increases from RPAP to TPAP via a therapeutic transition (TT) that typically occurs midway through the expiratory period.

[0018] According to several exemplary implementations, the patient selects RPAP at or above a predetermined minimum pressure.

[0019] TPAP is maintained for a period of approximately 0 to 2 seconds after the start of the next inhalation period.

[0020] According to several exemplary implementations, TPAP is maintained for a period of time until a trigger event occurs, including, but not limited to, the inhaled volume reaching the inhalation volume threshold at the start of the next inhalation period, the airflow rate reaching the airflow rate threshold at the start of the next inhalation period, and the patient flow rate being zero.

[0021] According to several exemplary implementations, the duration for which TPAP is maintained is proportional to the difference between RPAP and TPAP (i.e., the comfort setting), and therefore, if the difference is larger, TPAP is maintained for a longer period before the end of the exhalation period.

[0022] According to some exemplary implementations, the period during which the TPAP is maintained is proportional to the difference between the RPAP and the TPAP, and thus, when the difference is greater, the TPAP is maintained for a longer time before the end of the expiration period.

[0023] According to some exemplary implementations, the greater the difference between the RPAP and the TPAP (i.e., the comfort setting), the shorter the time the RPAP is maintained during the expiration period, and the longer the TPAP is maintained before the end of the expiration period.

[0024] According to some exemplary implementations, the TPAP and the time during which the TPAP is maintained are configured to maintain the patient's airway so as to avoid occlusion events.

[0025] According to some exemplary implementations, the RPAP is configured to reduce the mean airway pressure and improve the patient's comfort.

[0026] According to some exemplary implementations, the RPAP is maintained for substantially all of the inspiration period.

[0027] According to some exemplary implementations, the RPAP is maintained for a period until a trigger event occurs, including, but not limited to, until the air flow rate after the start of the next expiration period reaches an air flow rate threshold value and until the patient's flow rate becomes zero.

[0028] According to some exemplary implementations, the period during which the RPAP is maintained is proportional to the difference between the RPAP and the TPAP, and thus, when the difference is greater, the RPAP is maintained for a shorter time before the end of the expiration period.

[0029] According to some exemplary implementations, the pressure increases according to a sigmoid curve during the TT period. In some exemplary implementations, the pressure increases in proportion to at least one of the air flow rate in the patient's airway, the TPAP, and the comfort setting during the TT period.

[0030] In some exemplary implementations, the pressure decreases instantaneously from TPAP to RPAP during the inhalation period. In some other exemplary implementations, the pressure decreases according to a sigmoid function during the RT period. In some exemplary implementations, the pressure decreases during the RT period in proportion to at least one of the following: the airflow rate in the patient's airway, TPAP, and comfort setting.

[0031] According to several exemplary implementations, during the relaxation transition period, the pressure supplied into the patient's airway decreases from TPAP by an initial amount, then remains substantially constant at the intermediate pressure, and subsequently decreases from the intermediate pressure to RPAP in one or more additional steps. According to several specific implementations, the pressure supplied into the patient's airway decreases from the intermediate pressure to RPAP after the peak inhalation flow rate and / or before the peak expiratory flow rate.

[0032] An exemplary system for treating sleep-disordered breathing comprises a flow generator and a conduit operably connected to the flow generator. The conduit has an outlet configured to connect to the patient's respiratory system via a patient interface to supply pressure into the patient's airway over a period including multiple inhalation and multiple exhalation periods.

[0033] According to several exemplary implementations, the patient interface is a full-face mask, a partial-face mask, or a nasal pillow mask, and depending on the type of patient interface connected to the patient's respiratory system, RPAP, TPAP, or both RPAP and TPAP are adjusted. [Brief explanation of the drawing]

[0034] [Figure 1A] This 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 1B] Figure 1B is a schematic diagram of an exemplary positive airway pressure system during a portion of the expiratory phase of a patient's respiratory cycle. [Figure 2]This is a graph of the patient's airflow rate, along with a graph of the pressure profile of a prior art continuous positive airway pressure (CPAP) system. [Figure 3] This is a graph of the pressure profile of a prior art biphasic positive airway pressure (BPAP) system, associated with a graph of the patient's airflow rate. [Figure 4] This graph shows the pressure profile of another prior art positive airway pressure system, associated with a graph of the patient's airflow rate, where the applied pressure decreases in proportion to the patient's expiratory flow rate. [Figure 5] This is a graph of the pressure profile of a prior art airway passive pressure system, associated with a graph of the patient's airflow rate. [Figure 6] This is a graph of the assumed pressure profile, associated with a graph of patient airflow theorized by researchers in prior art. [Figure 7] This is a graph of another hypothetical pressure profile, related to a graph of patient airflow theorized by researchers in prior art. [Figure 8] This graph shows an 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. [Figure 9] This is a graph of one exemplary applied pressure profile of the positive airway pressure system of the present invention, associated with a graph of the patient's airflow rate. [Figure 10] These are three comparative graphs of exemplary applied pressure profiles of the positive airway pressure system of the present invention, associated with a graph of patient airflow. [Modes for carrying out the invention]

[0035] 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, in the systems and methods of the present invention, the pressure supplied into the patient's airway is intentionally reduced from therapeutic positive airway pressure to easing positive airway pressure after the end of the expiratory phase and maintained at a lower pressure throughout the inhalation phase and the following expiratory phase.

[0036] Unlike conventional positive airway pressure (CPAP) therapy systems and methods in which the inspiratory positive airway pressure (IPAP) is greater than or equal to the expiratory positive airway pressure (EPAP), according to the system and method of the present invention, the pressure during the inhalation period is generally lower than that during the expiratory period. This has been found to increase patient comfort while providing a therapeutic effect similar to that of conventional CPAP or BPAP devices in which IPAP is always greater than or equal to EPAP. One method that provides the above advantages previously discovered by the applicant is the incorporation of a passive resistor in the circuit of the positive airway pressure device, as described in International Patent Application No. PCT / US22 / 45897 (filed October 6, 2022), which is incorporated herein by reference. However, rather than the incorporation of a passive resistor or another similar device, the system and method of the present invention actively controls the positive pressure supplied to the patient to improve patient comfort and provide effective pressurization therapy.

[0037] Referring to some exemplary embodiments, specifically with reference to Figures 1A and 1B, the positive airway pressure system 200 of the present invention includes a flow generator 300 for providing a desired air pressure to a patient 600. The flow generator 300 is also referred to as a pressure generator. Specifically, the exemplary flow 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 flow generator 300 into a conduit 400, the conduit 400 having an inlet 402 operably connected to the flow generator 300, an outlet 404 operably connected to the patient's respiratory system, and an exhaust port 406 path along the conduit 400, preferably near the outlet 404. The outlet 404 may be any suitable form for operably connecting the air supplied from the flow generator 300 to the patient, for example, but not limited to, a full face mask, a partial face mask, a nasal pillow mask, or other suitable outlet. By adjusting the operating speed of the fan 302, the flow 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 on or near the flow generator that discharge the airflow generated by the fan.

[0038] Referring further to Figure 1A, during the inhalation phase of the patient's respiration, the diaphragm 608 lowers, expanding the lungs 606 and drawing air in through the nasal cavity 602 and pharynx 604. Conversely, referring to Figure 1B, during the exhalation phase of the patient's respiration, the diaphragm 608 and lungs 606 relax, pushing air out through the pharynx 604 and nasal cavity 602. Throughout both phases of the patient's respiratory cycle, the flow generator 300 supplies pressure through the conduit 400 and outlet 404 during the inhalation and exhalation phases of the patient's respiratory cycle. As used here, the nasal cavity 602 includes the mouth. Also, as used here, the patient's 600 “airway” includes the nasal cavity 602, pharynx 604, and lungs 606.

[0039] An 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 flow generator 300 and the pressure applied to 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 flow 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 a temperature sensor, an ambient pressure sensor, a gauge pressure sensor, a patient flow sensor, an ambient humidity sensor, a microphone, and an accelerometer.

[0040] Referring to Figure 2, in the most basic application of positive airway pressure therapy, continuous pressure is applied during both the inhalation and exhalation phases, commonly known as continuous positive airway pressure (CPAP). Referring to Figure 3, another system delivers two different pressures (BPAP). In either case, the pressure delivered during treatment varies depending on the patient, but the generally accepted theory is that a minimum pressure is required to keep the patient's airways open during the inhalation phase and allow airflow into the patient's respiratory system.

[0041] In known CPAP and BPAP systems, pressure is maintained throughout the entire individual inhalation and exhalation periods (even if the pressure changes during these periods in BPAP). In contrast, the present invention focuses on applying higher pressure, primarily but not exclusively, during the latter half of the exhalation period as a treatment method for sleep-disordered breathing. The applicant has found that this is the period when pressure is most critical for therapeutic effect. As detailed below, the present invention utilizes the viscoelastic properties of airway tissue by forcing expansion of airway tissue during the latter half of the exhalation period. Thus, in some cases, the application of higher pressure is partially extended into the subsequent inhalation period, maintaining the airway until lung volume increases during the first half of the inhalation period, at which point airway patency is maintained by tracheal traction. As used herein, “tracheal traction” means the effect of increasing lung volume by causing the diaphragm to move downward, which in turn moves the lungs downward, thereby pulling the trachea, larynx, and pharynx downward, resulting in structural hardening of these areas.

[0042] Conveniently, the present invention allows for a reduction in pressure during the remainder of the inhalation period, resulting in a decrease in mean airway pressure and improved overall patient comfort. This is in contrast to current treatments that reduce EPAP compared to IPAP to improve comfort. Importantly, the present invention maintains a minimum pressure throughout the patient's entire respiratory cycle, as will be discussed later.

[0043] Specifically, referring here to Figure 8, in an exemplary embodiment of the present invention, the use of the positive airway pressure system 200 of the present invention provides a pressure profile 100 that includes a relaxation positive airway pressure (RPAP) 150 applied during a portion of the patient's inhalation period 110, including the end of the patient's inhalation period 112 (i.e., the start of the next exhalation period 120), and a therapeutic positive airway pressure (TPAP) 130 applied during a portion of the exhalation period 120, including the end of the exhalation period 122 (i.e., the start of the next inhalation period 110). Importantly, and unique to the present invention, the TPAP 130 is greater than the RPAP 150. In other words, compared directly to existing BPAP systems where IPAP is greater than EPAP, according to the present invention, overall, the pressure supplied during the inhalation period 110 is lower than the pressure supplied during the exhalation period 120, and typically lower than the pressure at the end of exhalation 122.

[0044] As shown in Figure 8, the timing of the pressure transition between TPAP130 and RPAP150 is not directly linked to the timing of the transition between the inhalation period 110 and the expiratory period 120. Rather, the pressure is intentionally decreased from TPAP130 to RPAP150 via a relaxation transition (RT) 140 that occurs in the initial part of the inhalation period 110. Similarly, the pressure increases from RPAP150 to TPAP130 via a therapeutic transition (TT) 160 that occurs midway through the expiratory period 120. Some existing devices utilize a certain degree of ramp time or transition time, and prior to the present invention, the trigger event for these transitions was always the transition between the inhalation period and the expiratory period, and vice versa (see, for example, Figures 3-6). Specifically, prior to the present invention, it was generally supported that in order to obtain effective therapeutic relief, it was necessary to maintain IPAP for all or almost all of the inhalation period. As will be described in detail below, in some implementations of the present invention, the transition between the inhalation period 110 and the expiratory period 120 of patient respiration may influence the onset of the relaxation transition and / or therapeutic transition, and in addition to this, or instead, various additional factors are considered, resulting in a temporal separation between the transition between the inhalation period 110 and the expiratory period 120 of patient respiration and the pressure curve resulting from the implementation of the present invention.

[0045] Referring specifically to the therapeutic positive airway pressure (TPAP) 130 according to the present invention in the exemplary implementation shown in Figure 8, the TPAP 130 is configured to maintain the patient's airway to avoid obstructive events (e.g., apnea), as will be described in more detail below. In some exemplary implementations, the TPAP 130 is provided in a range of about 4 cmH2O to about 25 cmH2O, depending on the patient's specific therapeutic requirements. However, the TPAP can be provided in various other ranges, including, but not limited to, about 5 to 20 cmH2O, about 10 to 15 cmH2O, and about 8 to 15 cmH2O. While the TPAP 130 shown in Figure 8 is nearly uniform once TT160 is complete, the TPAP 130 may vary between about 0 cmH2O and about 3 cmH2O during any respiratory cycle. For example, the TPAP may be based at least in part on the patient's airflow and may change over time with the patient's respiration.

[0046] As described above, TPAP130 is applied for a sufficiently long time to maintain the airway from early inspiration until lung volume increases, at which point tracheal traction is at work to maintain airway patency. In some implementations of the present invention, this time is at least 0.5 seconds, but the duration for which TPAP130 is maintained may vary between approximately 0.05 seconds and approximately 5 seconds, depending on various factors described later. According to some exemplary embodiments, TPAP is maintained for approximately 0.5 seconds to approximately 4 seconds, approximately 1 second to approximately 3 seconds, or approximately 1 second to approximately 2 seconds.

[0047] According to several other implementations, the duration for which TPAP130 is maintained is determined by one or more environmental parameters, including at least one of atmospheric pressure, ambient temperature, humidity, and altitude above or below mean sea level. Similarly, according to several other exemplary implementations, the duration for which TPAP130 is maintained is determined by one or more physiological parameters of the patient, including at least one of the patient's height, weight, BMI, sex, age, pharyngeal collapsibility, measured respiratory rate, measured I:E ratio, measured tidal volume, and measured minute ventilation. The measurements can be determined based on a single measurement, or, in some preferred embodiments, based on multiple measurements taken over time, such as a rolling average. Variations in clinical requirements regarding the type and duration of CPAP therapy with respect to the above environmental and physiological parameters are well known and readily applicable to the present invention for those skilled in the art. As discussed here, the effects of clinical parameters, respiratory rate, I:E, and tidal volume tend to directly influence the duration of TPAP depending on the application time.

[0048] In addition to being determined by any of the above parameters, or instead, in some implementations, TPAP130 is maintained until a trigger event occurs. In some exemplary implementations, TPAP130 is maintained until the patient flow rate becomes substantially zero, i.e., until the start of the next inhalation period 110. In some other exemplary implementations, TPAP130 is maintained until the inhalation volume after the start of the next inhalation period 110 reaches a threshold (e.g., exceeds the threshold). In yet another exemplary implementation, TPAP130 is maintained after the start of the next inhalation period 110 until the airflow rate reaches a threshold (e.g., exceeds the threshold). In yet another exemplary implementation, TPAP130 is maintained after the start of the next inhalation period 110 until the derivative of the airflow rate (e.g., first-order, second-order, or higher-order) reaches a threshold. These trigger events are merely illustrative, and other trigger events can be used without departing from the spirit and scope of the invention.

[0049] With respect to the inhalation volume threshold in particular, while one example of an inhalation volume that triggers the termination of TPAP130 is 30 mL, the inhalation volume threshold can include any value in the range of about 10 mL to about 250 mL without departing from the spirit and scope of the invention. In some implementations, the inhalation volume threshold is determined based on the tidal volume measured during the previous inhalation period 110. For example, in some specific implementations, the inhalation volume threshold is between about 0% and about 50% of the tidal volume measured during the previous inhalation period 110. According to some exemplary embodiments, the inhalation volume threshold is between about 0% and about 40%, about 0% and about 30%, about 0% and about 20%, about 0% and about 10%, about 0% and about 5%, about 1% and about 5%, or about 1% and about 10% of the tidal volume measured during the previous inhalation period 110. The inhalation volume threshold may also be determined based on the average tidal volume measured during one or more previous inhalation periods 110, for example, at least three previous inhalation periods 110.

[0050] In particular, with respect to the airflow threshold, one exemplary airflow threshold that triggers the termination of TPAP130 is 2 L / min, but the airflow threshold may include any value in the range of about 1 L / min to about 10 L / min without departing from the spirit and scope of the invention. In some implementations, the airflow threshold is determined based on the peak inhalation flow rate measured during the previous inhalation period 110. For example, in some specific implementations, the airflow threshold is between about 0% and about 50% of the peak inhalation flow rate measured during the previous inhalation period 110. According to some exemplary embodiments, the airflow threshold is between about 0% and about 40%, about 0% and about 30%, about 0% and about 20%, about 0% and about 10%, about 0% and about 5%, about 0% and about 4%, about 0% and about 3%, about 0% and about 2%, or about 0% and about 1% of the peak inhalation flow rate measured during the previous inhalation period 110. The airflow threshold may be determined based on the average peak inhalation flow rate measured over one or more previous inhalation periods 110, for example, over at least three previous inhalation periods 110.

[0051] Naturally, it should be readily understood that tidal volume and airflow measurements are typically derived from estimated patient flow signals, which are themselves filtered versions of the mechanical flow signal. However, without departing from the spirit and scope of the invention, other means of directly or indirectly measuring inhalation volume and airflow are also possible.

[0052] Furthermore, while a trigger event may immediately cause the termination of TPAP130 and the start of RT140, some implementations involve an additional time period between the occurrence of such a trigger event and the termination of TPAP130 and the start of RT140. For example, in some exemplary implementations, TPAP130 is maintained for approximately 0 to 2 seconds after the trigger event. In some implementations, TPAP130 is maintained for a predetermined time after the start of the next inhalation period.

[0053] In other exemplary implementations, TPAP130 is maintained over a variable period based on one or more input values. For example, in some exemplary implementations, TPAP130 is maintained for a predetermined period between approximately 0% and approximately 50% of the expected length of the next inhalation period 110, after the start of the next inhalation period 110. In some exemplary implementations, TPAP is maintained between approximately 0% and approximately 40%, approximately 0% and approximately 30%, approximately 0% and approximately 40%, or approximately 0% and approximately 10% of the expected length of the next inhalation period 110. This expected length can be determined by any number of means known in the art, including using a moving average of several previous inhalation periods 110, or estimates partially based on metabolic requirements associated with age, sex, and BMI.

[0054] Referring specifically to the relaxation transition (RT) 140, regardless of how the termination of TPAP 130 is determined, the transition from TPAP 130 to RPAP 150, i.e., RT 140, may occur according to various different implementations. As shown in Figure 8, in one implementation example, during the inhalation period 110, the pressure decreases from TPAP 130 to RPAP 150 over a period of time. However, in some other exemplary implementation examples, the pressure decreases instantaneously from TPAP 130 to RPAP 150. As used here, “instantaneously” should be understood to mean as quickly as practically feasible given the mechanical and physical constraints of the system and the human body, and this includes less than 1.0 second in some embodiments, less than 0.5 seconds in some embodiments, less than 0.1 seconds in some embodiments, less than 0.05 seconds in some embodiments, and less than 0.01 seconds in some embodiments. According to some implementation examples, RT 140 occurs over a period of about 0 to 2 seconds. However, this time is typically not fixed but rather a function of one or more factors, such as patient flow rate. Further information regarding the overall shape of the RT140 will be discussed below.

[0055] Referring specifically to the relaxed positive airway pressure (RPAP) 150 according to the present invention, as will be described in more detail later, the RPAP 150 is configured to reduce mean airway pressure and improve patient comfort. In some exemplary implementations, the RPAP 150 is supplied in the range of about 1 cmH2O to about 20 cmH2O. In other exemplary embodiments, the RPAP is supplied in the range of about 1 to about 15 cmH2O, about 1 to about 10 cmH2O, or about 1 to about 5 cmH2O. In any case, a minimum pressure is maintained throughout the RPAP 150, which is lower than that of TPAP 130 unless otherwise specifically mentioned for a particular application and use. Maintaining a minimum pressure throughout the patient's respiratory cycle has proven important for several reasons. Supplying zero pressure or atmospheric pressure during the inhalation period 110 is uncomfortable for the patient. This is because the drop to atmospheric pressure requires a greater effort from the patient's diaphragm to draw sufficient negative pressure into the patient's lungs for breathing. This can cause discomfort, especially if the drop to zero pressure occurs suddenly near the start of inhalation. Furthermore, if the pressure drops to zero during inhalation, it can lead to airway narrowing, increasing the likelihood of needing higher pressure during exhalation or being exposed to higher pressure for extended periods, as will be discussed later. Additionally, by supplying continuous positive pressure, a constant flow of fresh air through the machine (e.g., conduit 400 and outlet 404) is maintained, which helps to avoid potential CO2 rebreathing.

[0056] The RPAP150 shown in Figure 8 is nearly uniform once RT140 is completed, but it is assumed that RPAP150 may fluctuate between approximately 0 cmH2O and approximately 5 cmH2O during any respiratory cycle. For example, since RPAP150 is at least partially based on the patient's airflow, it may fluctuate over time with the patient's respiration. Furthermore, although the RPAP150 shown in Figure 8 is the minimum pressure, it is assumed that, without departing from the spirit and scope of the invention, the pressure profile may drop below RPAP (including temporarily below 0 cmH2O) during RT140, between RT140 and TT160, or over a period of time between TT160. Similarly, without departing from the spirit and scope of the invention, the pressure may increase above RPAP over a period of time between RT140 and TT160. Such positive or negative pressure differences occurring between RT140 and TT160 are considered part of RPAP150 without departing from the spirit and scope of the invention.

[0057] As mentioned above, RPAP150 is applied over a period of time, but there is no minimum time required to maintain RPAP150. Rather, as will be discussed later, the reduced pressure during RPAP150 provides improved comfort to the patient, and the higher TPAP130 is considered more important for effective patient treatment. Therefore, in at least some implementations, the duration for which RPAP150 is maintained is the result of the time required to maintain TPAP130 to effectively provide patient treatment, and the time required to transition from TPAP130 to RPAP150 during RT140 and from RPAP150 to TPAP130 during TT160. However, in some implementations of the present invention, the duration for which RPAP150 is maintained is between approximately 0.05 seconds and approximately 5 seconds. As shown in the exemplary implementation in Figure 8, considering the relatively short period during which RT140 occurs, the duration for which RPAP150 is maintained includes most of the inhalation period 110. Furthermore, the duration for which RPAP 150 is maintained is expected to extend from approximately 0% to approximately 90% of the expected length of the next exhalation period 120 after the start of the next exhalation period. According to some exemplary embodiments, the duration for which RPAP is maintained after the start of the next exhalation period is between approximately 10% to approximately 90%, approximately 20% to approximately 90%, approximately 30% to approximately 90%, approximately 40% to approximately 90%, or approximately 50% to approximately 90% of the expected length of the next exhalation period. While RPAP may typically be extended only up to 90% of the expected length of the next exhalation period, according to some exemplary embodiments, the duration for which RPAP is maintained after the start of the next exhalation period is approximately 91%, approximately 92%, approximately 93%, approximately 94%, approximately 95%, approximately 96%, approximately 97%, approximately 98%, or approximately 99% of the expected length of the next exhalation period. In some specific implementations, RPAP is extended for approximately 0 to 5 seconds after the start of the next exhalation period 120. According to some exemplary embodiments, RPAP is extended for approximately 1 to 4 seconds, approximately 1 to 3 seconds, or approximately 1 to 2 seconds after the start of the next exhalation period.

[0058] According to several implementations, the duration for which RPAP150 is maintained is determined by one or more environmental parameters, including at least one of atmospheric pressure, ambient temperature, humidity, and altitude above or below mean sea level. Similarly, according to several other exemplary implementations, the duration for which RPAP150 is maintained is determined by one or more physiological parameters of the patient, including at least one of the patient's height, weight, BMI, degree of pharyngeal collapse, sex, age, measured respiratory rate, measured I:E ratio, measured tidal volume, and measured ventilation per minute. The measurements can be determined based on a single measurement, or, in some preferred embodiments, based on multiple measurements taken over time, such as a rolling average. Again, variations in clinical requirements regarding the type and duration of CPAP therapy with respect to the above environmental and physiological parameters are well known and readily applicable to the present invention for those skilled in the art. As discussed here, the effects of clinical parameters, respiratory rate, I:E, and tidal volume tend to directly influence the duration of RPAP by the time it is applied. However, RPAP may also depend on the patient's comfort level while awake.

[0059] In addition to being determined by any of the above parameters, or instead, in some implementations, RPAP150 is maintained until a trigger event occurs. In some exemplary implementations, RPAP150 is maintained until the patient flow rate becomes substantially zero, i.e., until the start of the next expiratory period 120. In some other exemplary implementations, RPAP150 is maintained until the patient flow rate after the start of the next expiratory period 120 reaches a threshold (e.g., until it falls below the threshold after a peak expiratory flow rate has occurred). In yet another exemplary implementation, RPAP150 is maintained after the start of the next expiratory period 120 until the derivative of the airflow rate (e.g., first, second, or higher order) reaches a threshold. These trigger events are merely illustrative, and other trigger events can be used without departing from the spirit and scope of the invention.

[0060] With respect to the airflow threshold in particular, one example of an airflow threshold that triggers the termination of RPAP150 is 2 L / min, but the airflow threshold can include any value in the range of about 1 L / min to about 5 L / min without departing from the spirit and scope of the invention. In some implementations, the airflow threshold is determined based on the peak expiratory flow rate measured during the next exhalation period 120 after RPAP150 has started. In some other implementations, the airflow threshold is determined based on the peak expiratory flow rate measured during the previous exhalation period 120. For example, in some specific implementations, the airflow threshold is between about 10% and about 100% of the peak expiratory flow rate measured during the previous exhalation period 120. According to some exemplary embodiments, the airflow threshold is between about 10% and about 90%, about 10% and about 80%, about 10% and about 70%, about 10% and about 60%, or about 10% and about 50% of the peak expiratory flow rate measured during the previous exhalation period 120. The airflow threshold is typically at least 10% of the peak expiratory flow rate, but according to some exemplary embodiments, the airflow threshold is about 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% of the peak expiratory flow rate measured during the previous expiratory period 120. The airflow threshold may also be determined based on the average peak expiratory flow rate measured during one or more previous expiratory periods 120, for example, at least three previous expiratory periods 120. Naturally, it will be readily understood that patient flow rate is typically estimated by filtering the mechanical flow rate (which is measured directly from the system flowmeter 304 or other similar sensor) to some extent. Since the mechanical flow rate is the sum of patient flow rate and leak flow rate, filtering can be used to remove the portion of leak flow rate. However, other means of measuring patient flow rate directly or indirectly are also possible without departing from the spirit and scope of the invention.

[0061] Furthermore, while a trigger event may immediately cause the termination of RPAP150 and the start of TT160, some implementations involve an additional time interval between the occurrence of such a trigger event and the termination of RPAP150 and the start of TT160. In some implementations, RPAP150 is maintained for a predetermined period after the start of the next exhalation period. For example, in some exemplary implementations, RPAP150 is maintained for approximately 0 to 2 seconds after the trigger event, e.g., the start of the next exhalation period 120. However, such delays can be applied to any trigger event.

[0062] In another exemplary implementation, RPAP150 is maintained over a variable period based on one or more input values. For example, in some exemplary implementations, RPAP150 is maintained between approximately 0% and approximately 80% of the expected length of the next exhalation period 120. In some exemplary embodiments, RPAP is maintained between approximately 10% and approximately 80%, approximately 20% and approximately 80%, approximately 30% and approximately 80%, approximately 40% and approximately 80%, or approximately 50% and approximately 80% of the expected length of the next exhalation period 120. This expected length can be determined by any number of means known in the art, including using a moving average of several previous exhalation periods 120, or estimates partially based on metabolic requirements associated with age, sex, and BMI.

[0063] Specifically, regarding the treatment transition (TT) 160, regardless of how the termination of RPAP 150 is determined, during the transition from RPAP 150 to TPAP 130, i.e., during TT 160, the pressure increases over a period of time from RPAP 150 to TPAP 130. Unlike RT 140, which can occur rapidly, TT 160 is considered preferable to occur over a longer period. This is because a sudden increase in pressure is easily perceived by the patient and reduces comfort. According to some exemplary implementations, RT 140 occurs over a relaxation transition period of approximately 250 milliseconds to approximately 5 seconds. However, this period is typically not fixed and is a function of one or more factors, such as patient flow rate. Additional information regarding the overall shape of RT 140 is provided below.

[0064] Referring here to both transitions occurring between RT140 and TT160, as mentioned above, RT140 and / or TT160 can occur over a period of time. In the exemplary implementation shown in Figure 8, both RT140 and TT160 provide a smooth transition between TPAP130 and RPAP150. However, the shape of the pressure profile 100 between RT140 and TT160 is not limited and can follow a function such as an exponential function, a power law function, a parabolic function, a sine function, and a sigmoid function, for example. While a smooth transition is considered preferable, in some embodiments, the shape of the pressure profile 100 between RT140 and / or TT160 may be linear.

[0065] In at least some situations, maintaining a smooth flow signal is advantageous because having a smooth curve is beneficial to avoid problems involving false triggers and event detections. The goal is to trigger when the patient's respiration requires a trigger, not due to irregular perturbations caused by CPAP control instability. Providing a smooth transition reduces the likelihood of false triggers, false event detections, and false flow limit measurements. False triggers, resulting from a mismatch between applied pressure and patient respiration, are likely to cause patient discomfort, and as mentioned above, increased discomfort can lead to reduced therapeutic use. Since RT140 typically begins near the transition from exhalation to inhalation, providing a smooth transition without false triggers during RT140 is particularly important. In contrast, TT160 generally occurs somewhere in the middle of the exhalation phase, making false triggers less likely to be noticed by the patient.

[0066] According to several exemplary implementations, the pressure profile 100 between RT140 and / or TT160 can be determined based on one or more physiological parameters, including at least one of the following: patient height, patient weight, patient BMI, patient pharyngeal collapse degree, 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 measurement can be determined based on a single measurement, or, in some preferred embodiments, based on multiple measurements taken over time, such as a rolling average. In some specific implementations, the pressure profile 100 between RT140 decreases in proportion to the increase in the patient's inspiratory flow rate, while in some other specific implementations, the pressure profile 100 between RT140 decreases in proportion to the decrease in the patient's inspiratory flow rate after the peak airflow rate. In yet another specific implementation, the pressure profile 100 between TT160 increases in proportion to the decrease in the patient's expiratory flow rate. Matching these pressure changes to the patient's own breathing, not only in timing but also in shape, helps to mask the pressure changes and improve patient comfort during the transition. Subsequently, if the patient requires higher TPAP, larger pressure changes can be allowed. The terms “proportional” and “proportionally,” as used here, are not limited to mathematically precise relationships and may include approximate or relatively closely related increases or decreases. Furthermore, the terms “proportional” and “proportionally” are used to describe both direct and inverse proportion.

[0067] According to several other implementation examples, the pressure profile 100 between RT140 and / or TT160 may be determined in relation to one or more environmental parameters, including at least one of atmospheric pressure, ambient temperature, humidity, and altitude above or below mean sea level.

[0068] In yet another implementation example, the pressure profile 100 between RT140 and / or TT160 may also be proportional to one or more aspects of the mechanical flow rate and pressure provided by the positive airway pressure system 200. For example, the pressure change between RT140 and / or TT160 may occur in proportion to the airflow rate supplied to the patient's airway. As described above, the measured airflow rate is typically derived from an estimated patient flow signal, which itself is a filtered version of the mechanical flow signal.

[0069] Similarly, the pressure profile 100 between RT140 and / or TT160 may also be proportional to TPAP130, RPAP150, and / or the difference between TPAP130 and RPAP150, i.e., the comfort setting 170, which will be further described below.

[0070] Below is one example formula for defining the curve between RT140 and / or TT160, where P del is the difference between RPAP150 and TPAP130 (i.e., comfort setting 170), z is time, and β is a coefficient that adjusts the shape of the sigmoid. The overall shape of the sigmoid is mapped to the expected time to give the shape of the sigmoid at each individual stage, for TPAP130 and similarly for RPAP150.

number

[0071] Figure 8 shows only two respiratory cycles, with an inhalation period of 110 and an exhalation period of 120. However, this is merely illustrative, and it should be understood that methods for treating sleep-disordered breathing are performed over periods including multiple inhalation and exhalation periods. Furthermore, while multiple inhalation and exhalation periods are typically consecutive, it is envisioned that the methods of the present invention can also be used with discontinuous inhalation and exhalation periods. That is, under certain circumstances, no pressure is applied to the patient's airway over a partial respiratory cycle, a complete respiratory cycle, or multiple respiratory cycles. In certain examples described later, this is due to the patient waking up. However, this is not always the case, and the methods of the present invention may include one or more partial or complete respiratory cycles in which no pressure is applied to the patient's airway as part of the usual intended treatment.

[0072] Furthermore, while the pressure profile 100 shown in Figure 8 repeats similarly between each respiratory cycle of the inhalation period 110 and the expiratory period 120, it is assumed that in some exemplary implementations, one or more of TPAP 130, RT 140, RPAP 150, and TT 160 may change between respiratory cycles. Some of these potential changes are described above (e.g., values ​​determined based on the average of measurements taken from the previous cycle), but with respect to TT 160 in particular, it should be understood that in some implementations of the present invention, the rate at which the pressure increases is modified during the expiratory period 120 to ensure that TPAP 130 is reached during TT 160 before the end of the expiratory period 120. If TPAP 130 is not reached before the end of the expiratory period 120, the time constant of the controller 500 of the positive airway pressure system 200 is updated, which sends an instruction to increase the pressure more rapidly during TT 160. Conversely, if the pressure reaches TPAP 130 before the target time threshold, the time constant is updated to slow down the rate at which the pressure increases during TT 160. Airways that are more prone to obstruction are thought to require earlier return to total pressure during the expiratory period of 120 compared to airways that are less prone to obstruction. In such situations, it is expected that an earlier return to TPAP 130 will be necessary.

[0073] To specifically refer to comfort setting 170, as mentioned above, comfort setting 170 is the difference between RPAP150 and TPAP130. In some exemplary implementations, comfort setting 170 is between approximately 0% and 50% of TPAP130. In some exemplary implementations, the comfort setting is between approximately 0% and 40%, 0% and 30%, 0% and 20%, or 0% and 10% of TPAP. In some specific implementations, comfort setting 170 is between approximately 0 cmH2O and 15 cmH2O. Typically, but not always, a larger comfort setting 170 is used when TPAP130 is higher, and a smaller comfort setting 170 is used when TPAP130 is lower. In some specific implementations, comfort setting 170 is provided in the range of approximately 3% to 4 cmH2O, 2% to 5 cmH2O, or 1% to 6 cmH2O. In some exemplary implementations, it is assumed that the patient can select any comfort setting 170, as long as the resulting RPAP 150 is above a predetermined minimum pressure. During operation, it is assumed that a physician or another specialist prescribes the TPAP value or range, and the patient selects a comfort setting. The positive airway pressure system 200 then develops a pressure profile using these two inputs and any number of other parameters as described above. After several days, weeks, months, etc., as the patient adapts to using the positive airway pressure system 200, the comfort setting may be changed automatically by the system itself or manually by the patient and / or physician. Thus, while some comfort settings may be used that do not completely eliminate all sleep disturbance events, these initial comfort settings increase patient adherence and allow for later reductions in the comfort setting over time, providing a more effective treatment. These adjustments can also be made based on sleep state, as will be further described below.

[0074] The various implementation examples and modifications described above for TPAP, RT, RPAP, and TT should be understood to be combinable in any way to achieve a desired pressure profile according to the present invention. To provide one specific example, the pressure profile may be based primarily on patient flow rate, but ensuring that the applied pressure reaches a predetermined maximum value during TPAP and does not fall below a minimum value during RPAP. Specifically, during the inhalation period, the pressure decreases from TPAP to RPAP in proportion to the decrease in patient inspiration from the peak airflow rate. Once the pressure reaches a minimum value in RPAP, it remains substantially constant throughout RPAP until the patient airflow rate reaches peak exhalation during the exhalation period. After peak exhalation, the pressure increases during TT in proportion to the decrease in patient inspiration from the peak exhalation airflow rate until it returns to a maximum value in TPAP.

[0075] Regardless of the specific method used in developing the pressure profile, as previously stated, TPAP130 is configured to maintain the patient's airway and avoid obstructive events, while RPAP150 is configured to reduce mean airway pressure to improve patient comfort. As used here, “obstructive event” may include any situation in which the soft tissues of the pharyngeal wall collapse inward, partially obstructing the airflow (hypopnea) or completely obstructing it (apnea). The duration of TPAP and the duration of TPAP are selected to increase lung volume at the end of each expiratory period, thereby increasing tracheal traction in the upper airway.

[0076] This invention utilizes the viscoelastic properties of airway tissue by forcing tissue expansion during the latter half of the expiratory phase and maintaining the airway until lung volume increases during the first half of the inhalation phase, thereby maintaining airway patency without additional pressure support through tracheal traction at that point.

[0077] A smaller airway cross-sectional area results in increased resistance and decreased airflow, increasing the likelihood of obstructive events such as apnea. However, by applying pressure to a patient's airway, force is transmitted to the airway tissue, where it is stored or "charged." It is important to recognize that the amount of "charge" imparted to the tissue depends not only on the magnitude of the force but also on the duration for which the force is applied. Specifically, because tissues have both elastic and viscous responses, a sudden force may produce an elastic response, but this reverses immediately upon removal of the force. In other words, as soon as the force is removed, the tissue elastically returns to its original shape. For a viscoelastic response to occur, where the tissue remains in an expanded shape for a period of time, the force must be applied over a period of time. In other words, once a viscoelastic response occurs, there is a delay after the force is removed before the tissue returns to its narrower shape.

[0078] Therefore, therapeutic positive airway pressure and the duration for which therapeutic positive airway pressure is maintained are selected to expand the viscoelastic structure within the airway, thereby viscoelastically expanding the airway cross-sectional area. More specifically, therapeutic positive airway pressure and the duration for which therapeutic positive airway pressure is maintained are selected to increase pharyngeal volume and thus reduce resistance in areas prone to obstruction for a period after the applied pressure has decreased. By concentrating pressure application at the end of the expiratory phase and the beginning of the inhalation phase, it becomes possible to have lower pressure for the remainder of the inhalation phase, resulting in a reduction in mean airway pressure and improving overall patient comfort, which is known to improve adherence to treatment.

[0079] The pressure profiles obtained from the present invention differ from any previously developed positive airway pressure systems. Specifically, unlike all previous systems, some exemplary pressure profiles of the present invention reduce the pressure well before the end of the inhalation period and maintain the reduced pressure not only at the start of the expiratory period but also for a period thereafter.

[0080] As mentioned above, the shape of the pressure curve between the relaxation transition and the therapeutic transition is not limited. Therefore, referring to Figure 9, in some exemplary implementations, the relaxation transition can occur in multiple stages to further enhance comfort. As shown in Figure 9, similar to the implementation shown in Figure 8, in the pressure profile 1100 of this exemplary implementation, the pressure decreases from TPAP 1130 to RPAP 1150 immediately after the start of the inhalation period 1110, via RT 1140 which begins during the early part of the inhalation period 1110. Similarly, the pressure increases from RPAP 1150 to TPAP 1130 via TT 1160 which occurs midway through the expiratory period 1120. However, unlike the implementation shown in Figure 8, during RT 1140 shown in Figure 9, there is an initial increase in pressure during the first period 1142, which is followed by the next decrease in pressure during the second period 1144.

[0081] During the first period 1142, the pressure delivered into the patient's airway decreases by an initial amount from TPAP 1130 and is maintained substantially constant at an intermediate pressure 1155, which is lower than TPAP 1130 but higher than RPAP 1150. In this exemplary implementation shown in Figure 9, the first period 1142 ends when the patient's airflow reaches the peak inhalation flow rate 1114, and the second period 1144 ends when the patient's airflow reaches the peak expiratory flow rate 1124. Therefore, the overall period over which RT 1140 occurs in Figure 9 is significantly longer than that of RT 140 shown in Figure 8. However, in another implementation, the first pressure drop from TPAP 1130 to the intermediate pressure 1155 occurs relatively quickly, and the second pressure drop from the intermediate pressure 1155 to RPAP 1150 occurs after the peak inhalation flow rate 1114. More specifically, in these implementations, the second pressure drop begins after the peak inhalation flow rate 1114 and continues until it is completed before the peak expiratory flow rate 1124. Alternative timings for the first and second pressure drops are also possible without departing from the spirit and scope of the invention.

[0082] Regardless of the specific timing of the two pressure drops, the initial pressure drop may be smaller, larger, or substantially equal to the subsequent pressure drop. In some exemplary implementations of the present invention, the initial pressure drop occurring during the first period 1142 is the difference between TPAP 1130 and RPAP 1150, i.e., between approximately 50% and approximately 80% of the comfort setting 1170. In some other exemplary implementations of the present invention, the initial pressure drop occurring during the first period 1142 is the difference between TPAP 1130 and RPAP 1150, i.e., between approximately 20% and approximately 50% of the comfort setting 1170. In some specific implementations, the initial pressure drop is approximately 2 cmH2O to approximately 4 cmH2O. Apart from including two separate pressure drops during RT1140, all other embodiments of TPAP130, RT140, RPAP150, and TT160 described above with respect to Figure 8 are equally applicable to TPAP1130, RT1140, RPAP1150, and TT1160 in Figure 9. Furthermore, although Figure 9 does not show only two pressure drops during RT1140, it is assumed that three or more pressure drops can occur without departing from the spirit and scope of the invention.

[0083] As described above, the overall shape of the pressure profile of the present invention conveniently takes into account the viscoelastic properties of the patient's airway. Referring here to Figure 10, three distinct exemplary pressure profiles 2100a to 2100c are shown, which provide substantially the same therapeutic effect according to the present invention. The pressure profiles shown in Figure 10 are simplified in several respects compared with the implementation examples illustrated in Figures 8 and 9 and described above. Specifically, similar to the pressure profiles described above, in each of the pressure profiles 2100a to 2100c shown in Figure 10, the pressure decreases from TPAP 2130a to 2130c through RT 2140a to 2140c to RPAP 2150a to 2150c, and the pressure increases from RPAP 2150a to 2150c through TT 2160a to 2160c to TPAP 2130a to 2130c. However, unlike the curved RT and TT shown in the previous implementation example, in each of the pressure profiles 2100a to 2100c shown in Figure 10, RT2140a to 2140c and TT2160a to 2160c are linear, and RT2140a to 2140c starts immediately at the beginning of the inhalation period 2110, i.e., at the end of the exhalation period 2120.

[0084] The second pressure profile 2100b is most similar to the previous pressure profiles 100 and 1100 in that TT2160b occurs approximately midway through the expiratory period 2120. Therefore, the therapeutic effect of the implementation example shown by the second pressure profile 2100b is substantially similar to the effect described above. That is, because the viscoelastic airway tissue is sufficiently "charged," even after the applied pressure decreases, the tissue remains in an expanded shape for a period of time, maintaining the airway from the initial stages of the inhalation period until lung volume increases, and at this point, tracheal traction maintains airway patency without additional pressure support.

[0085] Compared to the second pressure profile 2100b, in the first pressure profile 2100a, RPAP 2150a lasts considerably longer, and TT 2160a does not occur until just before the end of the expiratory period 2120. The duration for which TPAP 2130a occurs is also shorter compared to TPAP 2130b in the second pressure profile 2100b. The shorter time for which the pressure exceeds RPAP 2150a means that the airway tissue has less time to viscoelastically expand from the increased TPAP 2130b. However, the comfort setting 2170a in the first pressure profile 2100a (i.e., the difference between RPAP 2150a and TPAP 2130a) is also smaller than the comfort setting 2170b in the second pressure profile 2100b. In other words, because RPAP 2150a is greater, greater pressure is applied to the patient's airway throughout the initial part of the expiratory period 2120. As a result, it is not necessary to maintain TPAP2130a for as long as before the end of the expiratory period 2120 to provide the same overall effect on the viscoelastic tissue of the patient's airway.

[0086] Conversely, in the third pressure profile 2100c, the comfort setting 2170c (i.e., the difference between RPAP2150c and TPAP2130c) is greater than the comfort setting 2170b in the second pressure profile 2100b. However, in the third pressure profile 2100c, RPAP2150c is shorter, TT2160c occurs earlier, and the duration of TPAP2130c is longer compared to the second pressure profile 2100b. Therefore, even with a lower RPAP2150c, the earlier TT2160c and longer TTAP2130c result in the same overall effect on the viscoelastic tissue of the patient's airway.

[0087] Thus, although the pressure applied over time differs in each of the pressure profiles 2100a to 2100c, the overall therapeutic effect is substantially the same. In other words, the duration for which therapeutic positive airway pressure is maintained is proportional to the difference between palliative positive airway pressure and therapeutic positive airway pressure. Therefore, as this difference increases (i.e., the larger the difference), therapeutic positive airway pressure is maintained for a longer period before the end of the expiratory phase. Conversely, the duration for which palliative positive airway pressure is maintained is proportional to the difference between palliative positive airway pressure and therapeutic positive airway pressure. Therefore, as this difference increases (i.e., the larger the difference), palliative positive airway pressure is maintained for a shorter period before the end of the expiratory phase.

[0088] More specifically, as the difference between palliative positive airway pressure and therapeutic positive airway pressure increases, the duration for which palliative positive airway pressure is maintained during the expiratory phase decreases, and therefore therapeutic positive airway pressure is maintained for a longer period before the end of the expiratory phase.

[0089] The relationship between the comfort settings 2170a-c and the corresponding TPAP 2130a-c periods can be linear, a higher-order polynomial, a power law, an exponential function, or other general function. Alternatively or additionally, this relationship may be controlled by one or more of the following: physiological parameters, environmental parameters, or parameters related to the positive airway pressure system itself (e.g., applied airflow rate). Throughout testing, a smooth sigmoid has been shown to be extremely comfortable, and when this transition is implemented, even with a large difference between RPAP and TPAP, the transition is comfortable and unnoticeable when synchronized with the patient's exhalation.

[0090] Furthermore, although pressure profiles 2100a-c are somewhat simplified in Figure 10, it should be understood that the effects of pressure over time shown in Figure 10 are similarly applicable to all of the implementation examples and modifications described above with respect to Figures 8 and 9 with respect to the shape and timing of TPAP, RT, RPAP, and TT.

[0091] Furthermore, it should be understood that the methods described above can be modified 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 expiratory phase and to maintain low pressure for as long as possible. However, at the end of the expiratory phase, a sufficient increase is necessary to maintain airway patency. This can be achieved over a continuous range, from high comfort settings for shorter TPAP durations to longer TPAP durations with lower comfort settings. Essentially, for a given patient, a proportional product of these two factors (e.g., comfort setting and duration) is preferably maintained. 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 duration of TPAP can be increased until RPAP is completely eliminated.

[0092] Therefore, in some exemplary embodiments, the positive airway pressure (PAP) breathing system 200 can determine whether the patient is awake or asleep and change one or more parameters of the pressure profile accordingly. For example, TPAP may be reduced while the patient is awake or in a light sleep state, and TPAP may be gradually increased when the patient reaches a deep sleep state and / or is in a longer sleep state. Furthermore, the timing of TT and / or RT may also be influenced based on whether the patient is awake or asleep, which is substantially similar to the pressure profile described above with respect to Figure 10, except that TPAP, not RPAP, changes. For example, the PAP breathing system 200 may initially start with a low TPAP (i.e., a smaller comfort setting) when the patient is awake, and therefore, similar to the pressure profile 2100a shown in Figure 10, TT occurs fairly close to the end of the expiratory period. When the positive airway pressure system 200 determines that the patient is asleep, in addition to increasing TPAP, there is a correlated movement of TT away from the end of the expiratory period, similar to the pressure profiles 2100b and 2100c shown in Figure 10. By initiating TT earlier within the expiratory period, there is more time for a gradual transition from RPAP to TPAP while supplying the pressure necessary over time to provide the intended therapeutic effect, as described above with respect to Figure 10. Means of determining whether the patient is awake or asleep include, but are not limited to, detection of rapid eye movement (REM), detection of flow restriction or increased upper airway resistance, 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 is asleep.

[0093] As mentioned above, the exemplary implementations described above are envisioned to be carried out by the positive airway pressure system 200 via an algorithm that controls the device, for example, by adjusting the speed of the fan 302. As a further improvement of the present invention, it is envisioned that one or more physical components may be used to produce the effects described above. For example, a solenoid-operated valve may be provided in or near the outlet 404 and / or exhaust port 406 of the conduit 400 to selectively increase or decrease the pressure. Similarly, a fully pneumatic approach using a pneumatic function extractor (e.g., a pneumatic square root extractor) may be used instead of, or in addition to, the electronic control of the fan 302.

[0094] While the above description focuses on the application of the present invention to the treatment of sleep-disordered breathing, it should be understood that this system and method are also applicable to other forms of pressure support, i.e., ventilation therapy, such as mechanical ventilation. Although the specific pressure profile will vary depending on the type of treatment, many of the concepts regarding the transition between therapeutic and palliative positive airway pressure are similarly applicable as means of increasing comfort during inspiration, in substantially the same manner as described above. Specifically, certain ventilation therapies may require extending therapeutic positive airway pressure over a longer period of the inspiratory phase, but the details regarding the palliative and therapeutic transitions remain readily applicable.

[0095] 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. A method for treating sleep-disordered breathing, The step includes supplying pressure to the patient's airway over a period of time that includes multiple inhalation periods and multiple exhalation periods, 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 therapeutic positive airway pressure is greater than palliative positive airway pressure. The pressure is reduced from therapeutic positive airway pressure to palliative positive airway pressure after the end of the expiratory period.

2. The difference between palliative positive airway pressure and therapeutic positive airway pressure is approximately 3 cmH. ２ O~about 4cmH ２ The method according to claim 1, wherein the interval is O.

3. The method according to claim 1, wherein the difference between palliative positive airway pressure and therapeutic positive airway pressure is less than approximately 40% of therapeutic positive airway pressure.

4. The method according to claim 1, further comprising the step of the patient selecting a relaxed positive airway pressure greater than or equal to a predetermined minimum pressure.

5. The method according to claim 1, wherein therapeutic positive airway pressure is maintained for a certain period of time.

6. The method according to claim 5, wherein the aforementioned period lasts for about 0 seconds to about 2 seconds after the start of the next inhalation period.

7. The method according to claim 5, wherein the period lasts from the start of the next inhalation period for about 0% to about 50% of the expected length of the next inhalation period.

8. The method according to claim 5, wherein the aforementioned period continues until a trigger event occurs.

9. The method according to claim 8, wherein the trigger event is that the inhaled volume after the start of the next inhalation period reaches an inhalation volume threshold.

10. The method according to claim 9, wherein the inhalation volume threshold is determined based on the tidal volume measured during one or more previous inhalation periods.

11. The method according to claim 8, wherein the trigger event is that the airflow rate after the start of the next inhalation period reaches an airflow rate threshold.

12. The method according to claim 11, wherein the airflow threshold is determined based on peak inhalation flow rates measured during one or more previous inhalation periods.

13. The method according to claim 8, wherein the trigger event is a patient flow rate of zero.

14. The method according to claim 5, wherein the duration for which therapeutic positive airway pressure is maintained is proportional to the difference between palliative positive airway pressure and therapeutic positive airway pressure, and therefore, if the difference is larger, therapeutic positive airway pressure is maintained for a longer period before the end of the expiratory period.

15. The method according to claim 14, wherein if the difference between palliative positive airway pressure and therapeutic positive airway pressure is greater, the period during which palliative positive airway pressure is maintained during the expiratory period is reduced, and therefore therapeutic positive airway pressure is maintained for a longer period before the end of the expiratory period.

16. The method according to claim 5, wherein the therapeutic positive airway pressure and the time for which the therapeutic positive airway pressure is maintained are configured to maintain the patient's airway in order to avoid an obstructive event.

17. The method according to claim 1, wherein palliative positive airway pressure is maintained for a period of time.

18. The method according to claim 17, wherein the aforementioned period includes substantially the entire inhalation period.

19. The method according to claim 17, wherein the aforementioned period lasts for about 0 seconds to about 5 seconds after the start of the next exhalation period.

20. The method according to claim 17, wherein the period lasts from the start of the next exhalation period for about 0% to about 80% of the expected length of the next exhalation period.

21. The method according to claim 17, wherein the period continues until the airflow rate after the start of the next exhalation period reaches an airflow rate threshold.

22. The method according to claim 21, wherein the airflow threshold is the peak expiratory flow rate during the next expiratory period.

23. The airflow threshold is a predetermined airflow rate that is less than the peak expiratory flow rate measured during one or more previous exhalation periods. The method according to claim 21.

24. The method according to claim 17, wherein the period is continued until the patient flow rate becomes zero.

25. The method according to claim 17, wherein the duration for which palliative positive airway pressure is maintained is proportional to the difference between palliative positive airway pressure and therapeutic positive airway pressure, and therefore, if the difference is large, palliative positive airway pressure is maintained for a shorter time before the end of the expiratory period.

26. The method according to claim 1, wherein the palliative positive airway pressure is configured to reduce mean airway pressure and improve patient comfort.

27. The method according to claim 1, wherein during the expiratory period, the pressure is increased from palliative positive airway pressure to therapeutic positive airway pressure over the therapeutic transition period.

28. The method according to claim 27, wherein the pressure increases according to a sigmoid function.

29. The method according to claim 27, wherein the pressure increases in proportion to the airflow rate in the patient's airway.

30. The method according to claim 27, wherein the pressure increases in proportion to the positive pressure of the therapeutic airway.

31. The method according to claim 27, wherein the pressure increases in proportion to the difference between the relaxation positive airway pressure and the therapeutic positive airway pressure.

32. The method according to claim 1, wherein the pressure is instantaneously reduced from therapeutic positive airway pressure to palliative positive airway pressure during the inhalation period.

33. The method according to claim 1, wherein the pressure decreases from therapeutic positive airway pressure to relaxation positive airway pressure over a relaxation transition period.

34. The method according to claim 33, wherein the pressure decreases according to a sigmoid function.

35. The method according to claim 33, wherein the pressure decreases in proportion to the airflow rate in the patient's airway.

36. The method according to claim 33, wherein the pressure decreases in proportion to the positive pressure of the therapeutic airway.

37. The method according to claim 33, wherein the pressure decreases in proportion to the difference between the relaxation positive airway pressure and the therapeutic positive airway pressure.

38. The method according to claim 33, wherein during the relaxation transition period, the pressure supplied into the patient's airway is reduced by an initial amount from the therapeutic positive airway pressure, then maintained substantially constant at an intermediate pressure, and subsequently reduced from the intermediate pressure to the relaxation positive airway pressure in one or more additional steps.

39. The pressure supplied into the patient's airway is approximately 2 cmH. ２ O~about 4cmH ２ The method according to claim 38, wherein the initial amount during O is reduced.

40. The method according to claim 38, wherein the pressure supplied into the patient's airway is reduced by an initial amount between approximately 20% and approximately 50% of the difference between the relaxation positive airway pressure and the therapeutic positive airway pressure.

41. The method according to claim 38, wherein the pressure supplied into the patient's airway decreases from an intermediate pressure to a relaxed positive airway pressure after a peak inhalation flow rate.

42. The method according to claim 41, wherein the pressure supplied into the patient's airway decreases from intermediate pressure to relaxed positive airway pressure before peak expiratory flow.

43. A method for treating sleep-disordered breathing, The process includes the step of supplying pressure into the patient's airway over a period including multiple inhalation and multiple exhalation periods, wherein the pressure varies between a lower palliative positive airway pressure and a higher therapeutic positive airway pressure. The method involves a relaxed positive airway pressure during a portion of the inhalation period, including the end of the inhalation period, and during a portion of the expiratory period, including the start of the expiratory period.

44. The method according to claim 43, wherein the duration for which therapeutic positive airway pressure is maintained is proportional to the difference between palliative positive airway pressure and therapeutic positive airway pressure, and therefore, if the difference is larger, therapeutic positive airway pressure is maintained for a longer period before the end of the expiratory period.

45. The method according to claim 44, wherein if the difference between palliative positive airway pressure and therapeutic positive airway pressure is greater, the period during which palliative positive airway pressure is maintained during the expiratory period is reduced, and therefore therapeutic positive airway pressure is maintained for a longer period before the end of the expiratory period.

46. The method according to claim 44, wherein the pressure is increased from relaxation positive airway pressure to therapeutic positive airway pressure at least 0.5 seconds after the start of the expiratory period.

47. A method for treating sleep-disordered breathing, The process includes the step of supplying pressure into the patient's airway over a period including multiple inhalation and multiple exhalation periods, wherein the pressure varies between a lower palliative positive airway pressure and a higher therapeutic positive airway pressure. The pressure is therapeutic positive airway pressure during a portion of the expiratory period, including the end of the expiratory period. During a portion of the inhalation period, the pressure is maintained substantially constant at an intermediate pressure lower than therapeutic positive airway pressure and higher than palliative positive airway pressure. Next, the pressure decreases from intermediate pressure to positive pressure in the open airway.

48. The method according to claim 47, wherein the pressure decreases from an intermediate pressure to an open airway positive pressure after the peak inhalation flow rate and before the peak expiratory flow rate.

49. A system for treating sleep-disordered breathing, Flow generator and A conduit operably connected to a flow generator, comprising a conduit having an outlet configured to connect to the patient's respiratory system via a patient interface to supply pressure into the patient's airway over a period including multiple inhalation and multiple exhalation periods, The flow generator provides relaxed positive airway pressure during a portion of the inhalation period, including the end of the inhalation period. The flow generator supplies therapeutic positive airway pressure during a portion of the expiratory period, including the end of the expiratory period, and the therapeutic positive airway pressure is greater than the palliative positive airway pressure. The system reduces pressure from therapeutic positive airway pressure to palliative positive airway pressure after the end of the expiratory phase.

50. The patient interface is a full-face mask, a partial-face mask, or a nasal pillow mask. The system according to claim 49, wherein palliative positive airway pressure, therapeutic positive airway pressure, or both palliative and therapeutic positive airway pressure are adjusted according to the type of patient interface connected to the patient's respiratory system.

51. A computer equipped with a processor, The system according to claim 49, wherein the processor is configured to control a flow generator based on feedback provided from at least one of the following. A flow meter configured to measure the airflow rate supplied by a flow generator. A pressure sensor configured to measure the pressure supplied into a patient's airway. A patient flow sensor configured to monitor the airflow generated by the patient's lungs.

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