Control for pressure of a patient interface
A method of an apparatus control pressure in the patient interface. A vent valve may be used with a respiratory device, where the vent valve may selectively block fluid communication between components, such as the flow generator, the patient interface, and/or the vent. An expiratory flow model may be used to determine an expiratory characteristic such as an expiratory flow rate or pressure in the patient interface where an indicative measure may not be available. The expiratory flow model may receive inputs based on a measure of the patient's respiration, such as the tidal volume, peak inspiratory flow rate or length of inspiration. The expiratory characteristic may be used by a controller to control a pressure in the patient interface to provide respiratory therapy to a patient at or close to a target pressure.
1. An apparatus for controlling a supply of breathable gas at a positive pressure for amelioration or treatment of a respiratory disorder, the apparatus comprising:
a controller configured to:
control a therapy apparatus for providing a supply of breathable gas, the therapy apparatus configured to couple with a patient interface to deliver the supply of breathable gas to an airway of a patient,
determine an estimate of pressure in the patient interface for a breathing cycle of the patient based on an expiratory flow model, wherein the estimate of pressure in the patient interface is determined without using a measure indicative of pressure in the patient interface obtained during an expiratory portion of the breathing cycle, and
adjust a pressure in the patient interface based on the determined estimate of pressure in the patient interface and a target pressure.
2. The apparatus of claim 1 , wherein the expiratory flow model comprises one or a combination of a look-up table or a mathematical relationship.
3. The apparatus of claim 1 , wherein the expiratory flow model comprises a relationship between flow rate and time during the expiratory portion of the breathing cycle.
4. The apparatus of claim 3 , wherein the expiratory flow model is formed based on values sensed during an inspiratory portion of the breathing cycle.
5. The apparatus of claim 3 , wherein the expiratory flow model is calculated to model a flow verse time curve of typical patient expiration.
6. The apparatus of claim 3 , wherein the expiratory flow model is an inverted sawtooth.
7. The apparatus of claim 6 , wherein a slope and an amplitude of the inverted sawtooth are determined such that an expiratory volume of the inverted sawtooth equals a measured inspiratory volume and an expiratory time of the inverted sawtooth is a proportion of a measured inspiratory time.
8. The apparatus of claim 3 , wherein the expiratory flow model is an inverted step function.
9. The apparatus of claim 8 , wherein the inverted step function is calculated such that an expiratory volume of the inverted step function equals a measured inspiratory volume and an expiratory time of the inverted step function is a proportion of a measured inspiratory time.
10. The apparatus of claim 1 , wherein the controller is further configured to determine one of an estimate of expiratory flow rate or a phase of expiration based on the expiratory flow model.
11. The apparatus of claim 1 , wherein the controller is configured to determine a pressure adjustment for the pressure in the patient interface from a difference between the determined estimate of pressure in the patient interface and the target pressure.
12. The apparatus of claim 1 , wherein aspects of the expiratory flow model are determined based on a measure of inspiration.
13. The apparatus of claim 12 , wherein the measure of inspiration comprises one or more of: a ventilation volume, a tidal volume, a peak inspiratory flow, a length of time in inspiration, a lung compliance, a lung resistance, and/or an end of inspiration.
14. The apparatus of claim 1 , wherein the estimate of pressure in the patient interface is determined based on an elapsed time from a reference time.
15. The apparatus of claim 14 , wherein the reference time is a time of end of inspiration.
16. The apparatus of claim 14 , wherein the reference time is detected by the controller.
17. The apparatus of claim 1 , further comprising the therapy apparatus, wherein the therapy apparatus includes a blower.
18. The apparatus of claim 1 , further comprising the patient interface.
19. A control method in a processor, the control method comprising:
controlling a therapy apparatus for providing a supply of breathable gas, the therapy apparatus configured to couple with a patient interface to deliver the supply of breathable gas to an airway of a patient;
determining an estimate of pressure in the patient interface for a breathing cycle of the patient based on an expiratory flow model, wherein the estimate of pressure in the patient interface is determined without using a measure indicative of pressure in the patient interface obtained during an expiratory portion of the breathing cycle; and
adjusting a pressure in the patient interface based on the determined estimate of pressure in the patient interface and a target pressure.
20. An apparatus for controlling a supply of breathable gas at a positive pressure for amelioration or treatment of a respiratory disorder, the apparatus comprising:
a controller configured to:
control a therapy apparatus for providing a supply of breathable gas, the therapy apparatus configured to couple with a patient interface to deliver the supply of breathable gas to an airway of a patient,
determine an expiratory characteristic for a breathing cycle of the patient based on an expiratory flow model, wherein the expiratory characteristic is determined without using a measure indicative of the expiratory characteristic obtained during an expiratory portion of the breathing cycle, and
adjust a pressure in the patient interface based on the determined expiratory characteristic,
wherein the expiratory flow model comprises a relationship between flow rate and time during the expiratory portion of the breathing cycle,
wherein the expiratory flow model is an inverted sawtooth, and
wherein a slope and an amplitude of the inverted sawtooth are determined such that an expiratory volume of the inverted sawtooth equals a measured inspiratory volume and an expiratory time of the inverted sawtooth is a proportion of a measured inspiratory time.
21. An apparatus for controlling a supply of breathable gas at a positive pressure for amelioration or treatment of a respiratory disorder, the apparatus comprising:
a controller configured to:
control a therapy apparatus for providing a supply of breathable gas, the therapy apparatus configured to couple with a patient interface to deliver the supply of breathable gas to an airway of a patient,
determine an expiratory characteristic for a breathing cycle of the patient based on an expiratory flow model, wherein the expiratory characteristic is determined without using a measure indicative of the expiratory characteristic obtained during an expiratory portion of the breathing cycle, and
adjust a pressure in the patient interface based on the determined expiratory characteristic,
wherein the expiratory flow model comprises a relationship between flow rate and time during the expiratory portion of the breathing cycle,
wherein the expiratory flow model is an inverted step function, and
wherein the inverted step function is calculated such that an expiratory volume of the step function equals a measured inspiratory volume and an expiratory time of the inverted step function is a proportion of a measured inspiratory time.