Method and apparatus for detecting ineffective inspiratory efforts and improving patient-ventilator interaction

1. A system for detecting an ineffective effort of a patient being mechanically ventilated by a ventilator, the system comprising:

a flow sensor that is configured to:

monitor a respiratory flow of air of the patient during expiration that is after cycling of the ventilator and before triggering of the ventilator; and

generate a signal indicative of the respiratory flow of the patient during expiration;

a processing system that includes at least one processor, the processing system configured to:

determine a peak expiratory flow (PEF) of the patient based on the generated signal;

calculate a second derivative of the signal that is indicative of the respiratory flow of the patient during expiration;

determine an occurrence of a significant declivity within the signal when the second derivative of the signal is greater than a negative, non-zero threshold; and

detect perturbations within the generated signal by classifying the perturbations between at least ineffective efforts and non-ineffective efforts based on determination of the occurrence of the significant declivity within the signal.

2. A system as claimed in claim 1 , wherein said non-ineffective efforts include at least one of a signal representative of: cardiogenic oscillation, a cough, secretions, and/or a swallow.

3. A system as claimed in claim 1 , further comprising a noise filter that is configured to remove non-ineffective efforts from the generated signal.

4. A system as claimed in claim 1 , wherein the processing system is further configured to detect perturbations by detecting a local maximum within the generated signal.

5. A system as claimed in claim 2 , wherein the processing system is further configured to determine an elapsed time period since the onset of a potential swallow.

6. The system of claim 1 , wherein the processing system is further configured to determine that a cough has occurred when the PEF exceeds a threshold.

7. The system of claim 6 , whereby said threshold is approximately 200 L per minute.

8. The system of claim 4 , wherein the processing system is further configured to determine a flow value that occurs at said local maximum.

9. The system of claim 8 , wherein the processing system is further configured to determine that a potential swallow has occurred when the flow value is near zero.

10. The system of claim 9 , wherein the processing system is further configured to start a swallow timer when the flow value at said local maximum is near zero.

11. The system of claim 10 , wherein the processing system is further configured to determine that a swallow has occurred when said swallow timer is greater than about 500 ms.

12. The system of claim 1 , wherein the processing system is further configured to calculate a standard deviation based on the generated signal, wherein the negative threshold is a percentage of the standard deviation.

13. The system of claim 12 whereby said percentage is approximately 33%.

14. The system of claim 2 , wherein the processing system is further configured to modify the generated signal by removing a signal representative of cardiogenic oscillation by down-sampling or noise-filtering.

15. The system of claim 2 , wherein the processing system is further configured to modify the generated signal by removing a signal representative of cardiogenic oscillation by distinguishing cardiogenic oscillations on the basis of amplitude.

16. The system of claim 15 whereby cardiogenic signals have an amplitude of less than approximately 4 L per minute.

17. The system of claim 1 , wherein the processing system is further configured to determine an end of the significant declivity by detecting a local minimum.

18. The system of claim 17 , wherein the processing system is further configured to determine an amplitude of the significant declivity.

19. The system of claim 18 , wherein determination of the amplitude of the significant declivity includes subtracting a flow value at said local minimum from a flow value at a local maximum.

20. The system as claimed in claim 18 , wherein the processing system is further configured to determine that a cough has occurred when the amplitude of the significant declivity is greater than a threshold.

21. The system of claim 20 whereby said threshold is the PEF.

22. The system of claim 20 whereby said threshold is approximately 200 L/min.

23. A ventilator system for a patient, comprising:

a blower to produce a source of pressurized breathable gas;

a patient interface to deliver the breathable gas to the patient's airways; and

a system according to claim 1 ,

wherein the ventilator system controls the delivery of breathable gas from the blower based on a breathing effort measurement that is determined in accordance with the processing system.

24. A system as claimed in claim 23 wherein a Positive End Expiratory Pressure (PEEP) is adjusted based on the breathing effort measurement.

25. A system as claimed in claim 24 wherein when the patient has COPD said adjustment of PEEP is limited to 6 cm H2O.

26. A system as claimed in claim 24 , further comprising a sensor that is configured to measure oxygen saturation of the patient.

27. A system as claimed in claim 26 , wherein adjustment of PEEP is a function of the measured oxygen saturation.

28. A method of determining a measure of patient compliance with a mechanical ventilator, the method comprising:

detecting ineffective efforts with the system of claim 24 ;

recording, onto a storage medium, a signal that is indicative of the said ineffective efforts over time;

calculating a parameter based on the stored signal;

determining a measure of patient compliance based on the calculated parameter.

29. A method of detecting the onset of exacerbations of a patient that is mechanically ventilated, the method comprising:

detecting ineffective efforts of a patient with the system of claim 24 ;

determining a rate at which the ineffective efforts occur; and

determining that an onset of exacerbations have occurred when said rate changes.

30. A method of detecting the respiratory rate of a mechanically ventilated patient, the method comprising:

detecting the presence of ineffective efforts based on the system of claim 24 ;

monitoring a rate at which said ineffective efforts occur;

monitoring a rate of ventilator assisted breaths; and

determining a respiratory rate of the patient from a sum of the rate of ineffective efforts and the rate of ventilator assisted breaths.