Ventilator patient synchronization

• US 7,727,160 B2
• Filed: 11/28/2005
• Issued: 06/01/2010
• Est. Priority Date: 05/23/2001
• Status: Expired due to Fees

• Current Assignee: ResMed Pty Ltd. (ResMed Incorporated)
• Original Assignee: Resmed Limited (ResMed Incorporated)
• Inventors: Green, Paul Anthony, Bassin, David John
• Primary Examiner(s): Nasser; Robert L
• Application Number:
  US11/287,746
• Publication Number:
  US 20060079799A1
• Time in Patent Office: 1,646 Days
• Field of Search: None
• US Class Current: 600/529
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/0069 the speed thereof being controlled by respiratory parameters, e.g. by inhalation
• CPC Class Codes: A61M 16/024 including calculation means, e.g. using a processor
• CPC Class Codes: A61M 2016/0027 pressure meter
• CPC Class Codes: A61M 2016/0039 in the inspiratory circuit
• CPC Class Codes: A61M 2230/04 Heartbeat characteristics, e.g. ECG, blood pressure modulation

Abstract

A method and apparatus that provides an expert system for determining respiratory phase during ventilatory support of a subject. Discrete phase states are partitioned and prior probability functions and observed probability functions for each state are defined. The probability functions are based upon relative duration of each state as well as the flow characteristics of each state. These functions are combined to determine phase probabilities for each state using Bayes'"'"' theorem. The calculated probabilities for the states may then be compared to determine which state the subject is experiencing. A ventilator may then conform respiratory support in accordance with the most probable phase. To provide a learning feature, the probability functions may be adjusted during use to provide a more subject specific response that accounts for changing respiratory characteristics.

Claims

1. A method for estimating a subject'"'"'s respiratory phase by probability functions while the subject is being provided with respiratory support from a ventilator, said ventilator including a processor for computations, wherein the respiratory support of said ventilator matches the phase of the respiratory cycle of the subject, comprising the steps of:

partitioning the respiratory cycle into discrete phase states including respiratory states of inspiration and expiration and additional states within inspiration and expiration and

calculating the probabilities of the subject being in each phase state from probability functions.

2. The method of claim 1 wherein calculating the probabilities is a function of an observed probability determination L(Fj|Hi) and a prior probability determination L(Hi) and

the calculated probabilities L(Hi|Fj) are compared to an estimate of the actual phase in the patient'"'"'s respiratory cycle that the patient is

3. The method of claim 2 wherein the observed probability function L(Fj|Hi) is defined by dividing the range of values for flow or derivative of flow into discrete sub-ranges and then comparing those sub-ranges to each state and assessing probability based upon a typical or previously observed respiratory flow curve'"'"'s relationship with that sub-range.

4. The method of claim 3 wherein noise in the flow signal defines the smallest division into which flow signals may be divided.

5. The method of claim 2 wherein the prior probabilities of each particular state are determined by a function of relative duration of the state.

6. The method of claim 2 wherein the probabilities are determined from defined continuous likelihood density functions.

7. The method of claim 5 wherein the relative duration of each state is the ratio of each state'"'"'s duration to the duration of an entire respiratory cycle.

8. The method of claim 1 wherein the discrete phase states have durations derived by partitioning the respiratory cycle into sections in relation to a peak flow or differing rates of change of flow.

9. The method of claim 1 wherein the calculated probabilities are adjusted based upon state succession.

10. The method of claim 1 wherein the respiratory flow is observed or measured from the patient and the measure is applied to a probability function that is based upon predetermined likelihoods between that measure and each potential phase state.

11. The method of claim 10 wherein each predetermined likelihood is the likelihood that a particular range of flow is associated with a particular state.

12. A method for estimating a subject'"'"'s respiratory phase while the subject is being provided with respiratory support from a ventilator, said ventilator including a processor for computations, comprising the steps of:

partitioning the respiratory cycle into discrete phase states,

calculating the probabilities of the subject being in each phase state while providing respiratory support, and

utilizing previously calculated state probabilities to adjust prior probabilities wherein the respiratory patterns or characteristics of the subject are learned by said processor.

13. The method of claim 12 further comprising modifying the partitioning of phase states by using previously recorded breath data.

14. The method of claim 12 further comprising revising the relationship between observed respiratory characteristics and the likelihoods for each state by using previously recorded breath data.

15. A method for improving a ventilator'"'"'s synchronization with a patient, said ventilator including a processor for computation, wherein the most likely respiration phase is determined based on flow and rate of change of flow information using Bayes'"'"' theorem or some similar formula for assessing conditional probability, comprising the steps of:

dividing or partitioning the respiratory cycle into a number of distinct states,

making flow and pressure observations continuously and at each time point in a measuring

determining probabilities or likelihoods of a patient'"'"'s respiratory cycle being in each of the distinct states in a calculating step, and

determining the likelihood of the phase corresponding to each of the states.

16. The method of claim 15, wherein the distinct states comprise early inspiration, mid-inspiration, late inspiration, early expiration, mid-expiration, late expiration, pause, sigh and cough.

17. The method of claim 15 wherein determining the likelihood of the phase is by use of Bayes'"'"' theorem.

18. The method of claim 16, wherein in a system that distinguishes between a plurality of states, probability calculations for each distinct state are made according to the equation

L(Hi|Fj)=L(Hi)L(Fj|Hi)/Σ

_n(L(Hn)L(Fj|Hn).

19. The method of claim 18 further comprising assessing the prior likelihood of each of the identified states L(Hi).

20. The method of claim 19 wherein the prior likelihood is determined before use of a ventilator and/or adjusted during use.

21. The method of claim 18 wherein likelihoods are determined for the distinct respiratory states occurring given flow and rate of change of flow observations L(Hi|Fj).

22. The method of claim 21 comprising determining the patient'"'"'s phase as the phase which corresponds to the most likely state.

23. The method of claim 22 further comprising using the estimated respiratory phase to adjust the flow, volume or pressure of air being delivered to the patient in order to improve ventilator synchronization.

24. The method of claim 19, wherein the prior likelihood or prior probability of each state L(Hi) is chosen to depend upon the state and its relative duration.

25. The method of claim 24 wherein the dependence a ratio of the duration of the state to the duration of a respiratory cycle.

26. The method of claim 25 wherein the states are chosen on the basis of magnitude of flows.

27. The method of claim 26 wherein the respiratory cycle is divided according to the rate of change of flow.

28. The method of claim 15 wherein the number of states and their definitions are adaptively refined depending upon breath data.

29. The method of claim 28 wherein more states are used to define a region where the flow rate is changing rapidly.