Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M16/00—Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M16/00—Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes
  • A61M16/021—Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes operated by electrical means
  • A61M16/022—Control means therefor
  • A61M16/024—Control means therefor including calculation means, e.g. using a processor
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/08—Detecting, measuring or recording devices for evaluating the respiratory organs
  • A61B5/082—Evaluation by breath analysis, e.g. determination of the chemical composition of exhaled breath
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M16/00—Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes
  • A61M16/0003—Accessories therefor, e.g. sensors, vibrators, negative pressure
  • A61M2016/0015—Accessories therefor, e.g. sensors, vibrators, negative pressure inhalation detectors
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M16/00—Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes
  • A61M16/0003—Accessories therefor, e.g. sensors, vibrators, negative pressure
  • A61M2016/0015—Accessories therefor, e.g. sensors, vibrators, negative pressure inhalation detectors
  • A61M2016/0018—Accessories therefor, e.g. sensors, vibrators, negative pressure inhalation detectors electrical
  • A61M2016/0021—Accessories therefor, e.g. sensors, vibrators, negative pressure inhalation detectors electrical with a proportional output signal, e.g. from a thermistor
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M16/00—Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes
  • A61M16/0003—Accessories therefor, e.g. sensors, vibrators, negative pressure
  • A61M2016/0015—Accessories therefor, e.g. sensors, vibrators, negative pressure inhalation detectors
  • A61M2016/0018—Accessories therefor, e.g. sensors, vibrators, negative pressure inhalation detectors electrical
  • A61M2016/0024—Accessories therefor, e.g. sensors, vibrators, negative pressure inhalation detectors electrical with an on-off output signal, e.g. from a switch
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M16/00—Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes
  • A61M16/0003—Accessories therefor, e.g. sensors, vibrators, negative pressure
  • A61M2016/0027—Accessories therefor, e.g. sensors, vibrators, negative pressure pressure meter
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M2205/00—General characteristics of the apparatus
  • A61M2205/18—General characteristics of the apparatus with alarm
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M2205/00—General characteristics of the apparatus
  • A61M2205/35—Communication
  • A61M2205/3546—Range
  • A61M2205/3569—Range sublocal, e.g. between console and disposable
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M2205/00—General characteristics of the apparatus
  • A61M2205/35—Communication
  • A61M2205/3576—Communication with non implanted data transmission devices, e.g. using external transmitter or receiver
  • A61M2205/3592—Communication with non implanted data transmission devices, e.g. using external transmitter or receiver using telemetric means, e.g. radio or optical transmission
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M2205/00—General characteristics of the apparatus
  • A61M2205/50—General characteristics of the apparatus with microprocessors or computers
  • A61M2205/502—User interfaces, e.g. screens or keyboards
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M2205/00—General characteristics of the apparatus
  • A61M2205/50—General characteristics of the apparatus with microprocessors or computers
  • A61M2205/52—General characteristics of the apparatus with microprocessors or computers with memories providing a history of measured variating parameters of apparatus or patient
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M2205/00—General characteristics of the apparatus
  • A61M2205/58—Means for facilitating use, e.g. by people with impaired vision
  • A61M2205/582—Means for facilitating use, e.g. by people with impaired vision by tactile feedback
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
  • A61M2230/00—Measuring parameters of the user
  • A61M2230/40—Respiratory characteristics
  • A61M2230/43—Composition of exhalation
  • A61M2230/432—Composition of exhalation partial CO2 pressure (P-CO2)

Definitions

• the invention relates to determining concentrations of molecular gaseous species exhaled by subjects receiving pressure support therapy.
• determining the concentration of one or more gaseous molecular species in expired gas is difficult because expired gas is subject to dilution.
• the dilution may be caused by gas provided by the pressure support system during expiration. Increased leaks to the ambient atmosphere require increased gas to be provided as part of pressure support therapy during expiration causing increased dilution.
• One aspect of the invention relates to a pressure support system comprising a
• the pressure generator is configured to generate a pressurized flow of breathable gas for delivery to an airway of a subject.
• the gas delivery circuit is configured to deliver the pressurized flow of breathable gas from the pressure generator to the airway of the subject.
• the first sensor is configured to generate output signals conveying information related to the breathing phase of the subject.
• the second sensor is configured to generate output signals conveying information related to the composition of gas at or near the airway of the subject.
• the one or more processors are configured to execute computer program modules, the computer program modules comprising a control module, a therapy module, and an exhalation composition module.
• the control module is configured to control the pressure generator to adjust the pressurized flow of breathable gas such that pressure at or near the airway of the subject remains at or above an expiratory pressure level if the output signals generated by the first sensor indicate that the breathing of the subject is in an expiratory phase.
• the therapy pressure module is configured to set the expiratory pressure level implemented by the control module during expiratory phases of the breathing of the subject, wherein the therapy pressure module is configured such that during most expiratory phases the expiratory pressure level is set at a predetermined baseline expiratory pressure level, and such that intermittently the expiratory pressure level is lowered below the predetermined baseline expiratory pressure level.
• the exhalation composition module is configured to determine a concentration of a gaseous molecular species in gas exhaled from the lungs of the subject, wherein the exhalation composition module is configured such that the determination of the concentration of the gaseous molecular species in gas exhaled from the lungs of the subject is made based on output signals generated by the second sensor during the intermittent expiratory phases for which the expiratory pressure level is lowered below the predetermined baseline expiratory pressure level.
• Another aspect of the invention relates to a method of providing pressure support to a subject.
• the method comprises generating a pressurized flow of breathable gas for delivery to an airway of a subject; delivering the pressurized flow of breathable gas to the airway of the subject through a flow path; monitoring the breathing phase of the subject; collecting samples indicating a concentration of a gaseous molecular species within the flow path; adjusting the pressurized flow of breathable gas such that pressure at or near the airway of the subject remains at or above an expiratory pressure level if the breathing of the subject is in an expiratory phase; setting the expiratory pressure level implemented during expiratory phases of the breathing of the subject such that during most expiratory phases the expiratory pressure level is set at a predetermined baseline expiratory pressure level, and such that intermittently the expiratory pressure level is lowered below the predetermined baseline expiratory pressure level; and determining a concentration of the gaseous molecular species in gas exhaled from the lungs of the subject based on samples indicating the concentration of the gaseous mo
• Yet another aspect of the invention relates to a system configured to provide pressure support to a subject.
• the system comprises means for generating a pressurized flow of breathable gas for delivery to an airway of a subject; means for delivering the pressurized flow of breathable gas to the airway of the subject through a flow path;
• means for monitoring the breathing phase of the subject means for collecting samples indicating a concentration of a gaseous molecular species within the flow path; means for adjusting the pressurized flow of breathable gas such that pressure at or near the airway of the subject remains at or above an expiratory pressure level if the breathing of the subject is in an expiratory phase; means for setting the expiratory pressure level implemented during expiratory phases of the breathing of the subject such that during most expiratory phases the expiratory pressure level is set at a predetermined baseline expiratory pressure level, and such that during some non-consecutive expiratory phases the expiratory pressure level is lowered below the predetermined baseline expiratory pressure level; and means for determining a concentration of the gaseous molecular species in gas exhaled from the lungs of the subject based on samples indicating the concentration of the gaseous molecular species within the flow path during the non-consecutive expiratory phases for which the expiratory pressure level is lowered below the predetermined baseline expiratory pressure level.
• FIG. 1 illustrates a system configured to provide pressure support therapy to a subject, according to one or more embodiments of the invention.
• FIG. 2 illustrates a schematic model of the sampling of gas exhaled by a subject, in accordance with one or more embodiments of the invention.
• FIG. 3 illustrates a schematic model of the sampling of gas exhaled by a subject
• FIG. 4 a plot of pressure versus time dictated by a therapy regime, in accordance with one or more embodiments of the invention.
• FIG. 1 illustrates a system 10 configured to provide pressure support therapy to a
• the system 10 is also configured to determine the effectiveness of the provided pressure support therapy. This determination includes determining the concentration of one or more gaseous molecular species in gas exhaled by subject 12. For example, a
• determination of the concentration of carbon dioxide (CO 2 ) in gas exhaled by subject 12 ⁇ e.g., end-tidal CO 2 concentration
• determination of the concentration of carbon dioxide (CO 2 ) in gas exhaled by subject 12 ⁇ e.g., end-tidal CO 2 concentration
• system 10 is configured to provide determinations of composition of gas exhaled by subject 12 with relatively low levels of dilution caused by gases from other source ⁇ e.g., ambient atmosphere, the pressure support therapy, etc.).
• system 10 includes one or more of a pressure generator 14, electronic storage 16, a user interface 18, a first sensor 20, a second sensor 22, a processor 24, and/or other components.
• pressure generator 14 is configured to generate a pressurized flow of breathable gas for delivery to the airway of subject 12.
• the pressure generator 14 may control one or more parameters of the pressurized flow of breathable gas ⁇ e.g., flow rate, pressure, volume, humidity, temperature, gas composition, etc.) for therapeutic purposes, or for other purposes.
• pressure generator 14 may be configured to control the flow rate and/or pressure of the pressurized flow of breathable gas to provide pressure support to the airway of subject 12.
• the pressure generator 14 may include a ventilator, a positive airway pressure generator such as, for example, the device described in U.S. Patent No. 6,105,575, hereby incorporated by reference in its entirety, and/or other pressure generation devices.
• the pressure support provided by subject 14 via the pressurized flow of breathable gas may include, for example, non-invasive ventilation, positive airway pressure support, bi-level support, BiPAP®, and/or other types of pressure support therapy.
• the pressurized flow of breathable gas is delivered to the airway of subject 12 via a gas delivery circuit 26.
• Gas delivery circuit 26 is configured to communicate the pressurized flow of breathable gas generated by pressure generator 14 to the airway of subject 12.
• gas delivery circuit 26 includes a conduit 28 and an interface appliance 30.
• Conduit conveys the pressurized flow of breathable gas to interface appliance 30, and interface appliance 30 delivers the pressurized flow of breathable gas to the airway of subject 12.
• Some examples of interface appliance 30 may include, for example, a nasal cannula, a nasal mask, a nasal/oral mask, a full face mask, a total face mask, and/or other interface appliances that communication a flow of gas with an airway of a subject.
• the present invention is not limited to these examples, and contemplates delivery of the pressurized flow of breathable gas to subject 12 using any subject interface.
• gas delivery circuit 26 is illustrated in FIG. 1 as a single-limbed circuit for the delivery of the pressurized flow of breathable gas to the airway of subject 12, this is not intended to be limiting.
• the scope of this disclosure includes double-limbed circuits having a first limb configured to both provide the pressurized flow of breathable gas to the airway of subject 12, and a second limb configured to selectively exhaust gas from gas delivery circuit 26 (e.g., to exhaust exhaled gases).
• the illustration of interface appliance 30 as a single device is not intended to be limiting. It will be appreciated that interface appliance 30 may include at least two separate interface appliances.
• a first interface appliance e.g., a full face mask, a total face mask, etc.
• a second interface appliance e.g., a nasal cannula, etc.
• parameters of the gas received from the airway of subject 12 can be measured (e.g., composition).
• electronic storage 16 comprises electronic storage media that electronically stores information.
• the electronic storage media of electronic storage 16 may include one or both of system storage that is provided integrally (i.e., substantially nonremovable) with system 10 and/or removable storage that is removably connectable to system 10 via, for example, a port (e.g., a USB port, a firewire port, etc.) or a drive (e.g., a disk drive, etc.).
• a port e.g., a USB port, a firewire port, etc.
• a drive e.g., a disk drive, etc.
• Electronic storage 16 may include one or more of optically readable storage media (e.g., optical disks, etc.), magnetically readable storage media (e.g., magnetic tape, magnetic hard drive, floppy drive, etc.), electrical charge-based storage media (e.g., EEPROM, RAM, etc.), solid-state storage media (e.g., flash drive, etc.), and/or other electronically readable storage media.
• Electronic storage 16 may store software algorithms, information determined by processor 24, information received via user interface 18, and/or other information that enables system 10 to function properly.
• Electronic storage 16 may be (in whole or in part) a separate component within system 10, or electronic storage 16 may be provided (in whole or in part) integrally with one or more other components of system 10 (e.g., generator 14, user interface 18, processor 24, etc.).
• User interface 18 is configured to provide an interface between system 10 and subject 12 through which subject 12 may provide information to and receive information from system 10. This enables data, cues, results, and/or instructions and any other communicable items, collectively referred to as "information," to be communicated between the subject 12 and one or more of generator 14, electronic storage 16, and/or processor 24.
• Examples of interface devices suitable for inclusion in user interface 18 include a keypad, buttons, switches, a keyboard, knobs, levers, a display screen, a touch screen, speakers, a microphone, an indicator light, an audible alarm, a printer, a tactile feedback device, and/or other interface devices.
• user interface 18 includes a plurality of separate interfaces.
• user interface 18 includes at least one interface that is provided integrally with generator 14.
• user interface 18 is also contemplated by the present invention as user interface 18.
• user interface 18 may be integrated with a
• removable storage interface provided by electronic storage 16.
• information may be loaded into system 10 from removable storage (e.g., a smart card, a flash drive, a removable disk, etc.) that enables the user(s) to customize the implementation of system 10.
• removable storage e.g., a smart card, a flash drive, a removable disk, etc.
• Other exemplary input devices and techniques adapted for use with system 10 as user interface 18 include, but are not limited to, an RS-232 port, RF link, an IR link, modem
• any technique for communicating information with system 10 is contemplated by the present invention as user interface 18.
• the first sensor 20 is configured to generate output signals conveying information related to one or more parameters of the pressurized flow of breathable gas.
• the one or more parameters may include, for example, one or more of a flow rate, a volume, a pressure, humidity, temperature, acceleration, velocity, acoustics, changes in a parameter indicative of respiration, and/or other gas parameters.
• the output signals generated by first sensor 20 convey information related to the breathing phase of subject 12.
• the first sensor 20 may include one or more sensors that measure such parameters directly ⁇ e.g., through fluid communication with the pressurized flow of breathable gas at pressure generator 14 or in gas delivery circuit 26).
• the first sensor 20 may include one or more sensors that generate output signals related to one or more parameters of the pressurized flow of breathable gas indirectly.
• first sensor 20 may include one or more sensors configured to generate an output based on an operating parameter of pressure generator 14 (e.g., a valve driver or motor current, voltage, rotational velocity, and/or other operating parameters), and/or other sensors.
• first sensor 20 is illustrated as a single sensor at a single location within gas delivery circuit 26, this is not intended to be limiting.
• the first sensor 20 may include a plurality of sensors which may be located proximately or separately with respect to each other. Sensors providing the functionality attributed herein to first sensor 20 may be disposed in any of a plurality of locations, such as for example, within pressure generator 14, within (or in communication with) conduit 28, within (or in communication with) interface appliance 30, and/or other locations.
• the second sensor 22 is configured to generate output signals conveying information related to the composition of gas at or near the airway of subject 12.
• the output signals generated by second sensor 22 convey information related to the
• the output signals generated by second sensor 22 may be used to determine end-tidal CO 2 for subject 12.
• detecting CO 2 concentration in a sample of alveolar gas will provide enhanced accuracy.
• obtaining such a sample in a sampling chamber accessible to second sensor 22 is easy, as all of the gas expired from the lungs of subject 12 must flow out of interface appliance 30.
• obtaining an alveolar gas sample may be more difficult because as gas exits the airway of subject 12 it can be actively diluted by air supplied by pressure generator 14 in an effort to maintain pressure in the presence of leaks to ambient air.
• interface appliance 30 may include two separate interface appliances, one to deliver the pressurized flow of breathable gas, and one to acquire samples of gas exhaled by subject 12.
• interface appliance 30 may include a mask configured to deliver the pressurized flow of breathable gas, and a nasal cannula underneath the mask that is installed in the nares of subject 12 to collect gas exhaled by subject 12.
• Processor 24 is configured to provide information processing capabilities in system 10.
• processor 24 may include one or more of a digital processor, an analog processor, a digital circuit designed to process information, an analog circuit designed to process information, a state machine, and/or other mechanisms for electronically processing information. Although processor 24 is shown in FIG. 1 as a single entity, this is for illustrative purposes only. In some implementations, processor 24 may include a plurality of processing units. These processing units may be physically located within the same device (e.g., pressure generator 14), or processor 24 may represent processing functionality of a plurality of devices operating in coordination.
• processor 24 may be configured to execute one or more
• the one or more computer program modules may include one or more of a breath phase module 32, a control module 34, a therapy pressure module 36, a exhalation composition module 38, and/or other modules.
• Processor 24 may be configured to execute modules 32, 34, 36, and/or 38 by software; hardware; firmware; some
• modules 32, 34, 36, and 38 are illustrated in FIG. 1 as being co-located within a single processing unit, in implementations in which processor 24 includes multiple processing units, one or more of modules 32, 34, 36, and/or 38 may be located remotely from the other modules.
• the description of the functionality provided by the different modules 32, 34, 36, and/or 38 described below is for illustrative purposes, and is not intended to be limiting, as any of modules 32, 34, 36, and/or 38 may provide more or less functionality than is described.
• processor 24 may be configured to execute one or more additional modules that may perform some or all of the functionality attributed below to one of modules 32, 34, 36, and/or 38.
• the breath phase module 32 is configured to determine the phase of respiration of subject 12.
• the breath phase module 32 determines the phase of respiration based on the output signals generated by first sensor 20. For example, fluctuations in flow rate, pressure and/or other parameters indicated in the output signals generated by first sensor 20 may be implemented by breath phase module 32 to determine the phase of respiration of subject 12. Determining the phase of respiration includes determining whether the breathing of subject 12 is in the inspiratory phase or the expiratory phase.
• breath phase module 32 is configured to determine more than breathing transitions from inspiratory phase to expiratory phase and vice versa. For example, may be configured to determine when the breathing of subject 12 reaches one or more points in the inspiratory phase and/or expiratory phase.
• processor 24 includes one or more processors within a first device that includes pressure generator 14, and one or more processors within a second device configured to determine information related to the composition of gas exhaled by subject 12.
• breath phase module 32 may include one or more modules executed on the device configured to determine information related to the composition of gas exhaled by subject 12. The one or more modules of the second may determine respiration phase based on determinations of respiration phase made by the first device in order to adjust the pressurized flow of breathable gas according to the therapy regime.
• the control module 34 is configured to control pressure generator 14 to adjust the pressurized flow of breathable gas such that pressure at or near the airway of subject 12 follows a therapy regime.
• the therapy regime may dictate a target pressure at or near the airway of subject 12 as a function of the phase of the breathing of subject 12.
• breath phase module 32 determines the phase of respiration of subject 12
• control module 34 implements this determination to determine the target pressure at or near the airway of subject 12 dictated by the therapy regime.
• the control module 34 then controls pressure generator 14 to adjust the pressurized flow of breathable gas to achieve and/or maintain this target pressure.
• the therapy regime specifies an expiratory pressure level and an inspiratory pressure level.
• the inspiratory pressure level is substantially higher than the expiratory pressure level.
• control module 34 controls pressure generator 14 to adjust the pressurized flow of breathable gas such that pressure at or near the airway of subject 12 is adjusted toward the inspiratory pressure level. Maintenance of relatively high pressure at or near the airway of subject 12 during the inspiratory phase of respiration makes it easier for subject 12 to inhale.
• control module 34 controls pressure generator 14 to adjust the pressurized flow of breathable gas such that pressure at or near the airway of subject 12 is reduced to less than inspiratory phase pressure so that subject 12 does not have to exhale "against" too much pressure.
• control module 34 does not permit pressure at or near the airway of subject 12 to fall below the expiratory pressure level.
• the expiratory pressure level may be set to a level that will facilitate exhalation by subject 12, and yet safeguards against alveolar deterioration and prevent airway closure.
• the therapy pressure module 36 is configured to adjust the pressures dictated by the therapy regime. These adjustments include adjusting the pressures dictated by the therapy regime to facilitate determinations of end-tidal CO 2 .
• control module 34 causes pressure generator 14 to adjust the
• the expiratory pressure level is reached relatively soon after respiration changes from the inspiratory to expiratory phase, which results in an increase in flow rate of the pressurized flow of breathable gas to maintain pressure at or near the airway of subject 12.
• obtaining accurate end-tidal C0 2 requires obtaining sufficiently pure expired gas for second sensor 22 to measure CO 2 composition with relatively low amounts of dilution.
• the increase in flow rate of the pressurized flow of breathable gas during expiration to maintain the expiratory pressure level is a primary source of dilution of gas exhaled by subject 12, and makes obtaining sufficiently pure expired gas for second sensor 22 to measure CO 2 composition challenging.
• FIG. 2 is a schematic model of the sampling of gas exhaled by a subject.
• the shaded box represents a volume 40 defined by an interface appliance similar to or the same as interface appliance 30 (shown in FIG. 1 and described herein) and the airway of the subject.
• the sample of gas used by a composition sensor that is the same as or similar to second sensor 22 (shown in FIG. 1 and described herein) is labeled as element 42.
• the dark shading represents gas that is purely expired from the alveoli of the lungs, and therefore contains an alveolar CO 2 concentration.
• the light shading represents other gases that function to dilute the expired gas.
• the diluting gases comprise primarily the pressurized flow of breathable gas provided from a pressure generator that is the same as or similar to pressure generator 14 (shown in FIG. 1 and described herein). As was discussed above, leaks 44 between the volume 42 and atmosphere require an increased amount of gas to be delivered in pressurized flow of breathable gas to maintain pressure, thereby increasing dilution.
• therapy pressure module 36 is configured to sporadically adjust the expiratory pressure level of the therapy regime to reduce dilution of expired gas sampled by second sensor 22. This results in the expiratory pressure level for most expiratory phases being set at a baseline expiratory pressure level that facilitates expiration while providing the benefits of airway and/or lung pressure support to subject 12. However, during some expiratory phases, therapy pressure module 36 lowers the expiratory pressure implemented by control module 34 to reduce dilution of expired gases during these expiratory phases.
• FIG. 3 shows volume 40 (also depicted in FIG. 2 and discussed above) during an expiratory phase in which the flow rate of the pressurized flow of breathable gas is reduced, if not ceased altogether.
• this tends to decrease the dilution of expired gases, thereby enabling a more accurate determination of end-tidal C0 2 .
• the reduction in flow of the pressurized flow of breathable gas may further enable the subject to exhale more completely, thereby increasing the volume of expired gas introduced into volume 40 and further decreasing dilution from other gases.
• the reduction of the expiratory pressure level uniformly across respiration may reduce the benefits of the pressure support provided by system 10.
• therapy pressure module 36 enables samples of less diluted expiratory gas to be taken without detrimentally impacting the therapy received by subject 12.
• FIG. 4 illustrates a plot of pressure versus time dictated by a therapy regime.
• pressure dictated by the therapy regime is at an inspiratory pressure level.
• pressure dictated by the therapy regime is at a baseline expiratory pressure level 46.
• the expiratory pressure level is reduced to permit sampling of end-tidal CO 2 with reduced dilution. This reduction in expiratory pressure level may be applied throughout a given expiratory phase, such as is shown in expiratory phase 48, or may be applied during only a portion of the given expiratory phase, such as is shown in expiratory phase 50.
• the determination of which expiratory phases should be provided with a reduced expiratory pressure level by therapy pressure module 36 may be made with a periodicity.
• This periodicity may be quantified by a number of breaths (e.g., expiratory pressure level is reduced every X breaths), and/or by passage of time (e.g., expiratory level is reduced every X seconds).
• This periodicity may be a configurable setting that can be selectively configured by a user via user interface 18.
• the determination of which expiratory phases should be provided with a reduced expiratory pressure level by therapy pressure module 36 may be made stochastically or even randomly (or pseudo- randomly) by therapy pressure module 36. In this embodiment, some control over the relative frequency with which a reduced expiratory pressure level is provided may be provided to a user via user interface 18.
• the amount of reduction below the baseline expiratory pressure may be a configurable setting that can be selectively configured by a user via user interface 18.
• therapy pressure module 36 is configured that for breaths during which the expiratory pressure level is not set below the baseline expiratory pressure level there is still some variance between the expiratory pressure level.
• therapy pressure module 36 may be configured to vary the expiratory pressure level in a periodic sinusoidal fashion.
• the range of expiratory pressures over which the sinusoid travels may be configured such that the expiratory pressure level falls below the baseline expiratory pressure level only at or near the minima of the sinusoid.
• the exhalation composition module 38 is configured to determine a concentration of a gaseous molecular species in gas exhaled from the lungs of subject 12 based on output signals generated by second sensor 22. In one embodiment, this includes a determination of end-tidal CO 2 .
• the determination of the concentration of the gaseous molecular species is made by exhalation composition module 38 using only output signals generated during expiratory phases in which therapy pressure module 36 has set the expiratory pressure level below the baseline expiratory pressure level. This ensures that the determination is based on samples of the concentration of the gaseous molecular species that are less distorted by dilution than samples of the concentration of the gaseous molecular species taken during expirations in which the expiratory pressure level is at or above the baseline expiratory pressure level.
• the effectiveness of the pressure support provided by system 10 may be determined. This determination may be made by processor 24, and may be based on determinations of other respiratory parameters measured and/or estimated from, for example, output signals generated by first sensor 20. Determinations of the effectiveness of the pressure support and/or the determinations of the gaseous molecular species in gas exhaled from the lungs of subject 12 may be implemented by processor 24 to titrate the pressure support. For example, the therapy regime
• control module 34 to determine control of pressure generator 14 may be adjusted based on such determinations to enhance the therapeutic benefit of the pressure support to subject 12.

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• 2010
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