Leak determination in a breathing assistance system

1. A breathing assistance system for providing breathing assistance to a patient, comprising:

a pneumatic system for providing breathing assistance to a patient; and

a controller configured to control one or more operational parameters of the pneumatic system, the controller configured to estimate a leak flow in a breathing assistance system including a ventilation device connected to a patient by:

accessing data of a flow waveform indicating the flow of gas between the ventilation device and the patient;

identifying a specific portion of the flow waveform as a steady phase portion; and

performing a linear regression of the identified portion of the flow waveform to determine an estimated leak flow in the breathing assistance system;

wherein identifying the steady phase portion comprises:

identifying a reference period of the flow waveform;

determining a representative flow rate for the reference period;

determining a series of one or more consecutive qualifying periods of the flow waveform having representative flow rates that vary from the representative flow rate for the reference period by less than a predetermined amount; and

defining the steady phase portion as including the reference period and the series of one or more consecutive qualifying periods.

2. A controller for a breathing assistance system, the controller including logic instructions embodied in tangible computer readable media and executable by one or more processors to:

access data of a flow waveform indicating the flow of gas between the ventilation device and the patient;

identify a specific portion of the flow waveform as a steady phase portion; and

perform a linear regression of the identified portion of the flow waveform to determine an estimated leak flow in the breathing assistance system;

wherein identifying the steady phase portion comprises:

identifying a reference period of the flow waveform;

determining a representative flow rate for the reference period;

determining a series of one or more consecutive qualifying periods of the flow waveform having representative flow rates that vary from the representative flow rate for the reference period by less than a predetermined amount; and

defining the steady phase portion as including the reference period and the series of one or more consecutive qualifying periods.

3. A method for estimating a leak flow in a breathing assistance system including a ventilation device connected to a patient, the method comprising:

accessing data associated with a flow waveform indicating the flow of gas between the ventilation device and the patient;

identifying a steady phase portion near the end of an exhalation phase; and

performing a linear regression of the identified portion of the flow waveform to determine an estimated leak flow in the breathing assistance system;

wherein identifying the steady phase portion comprises:

identifying a reference period of the flow waveform;

determining a representative flow rate for the reference period;

determining a series of one or more consecutive qualifying periods of the flow waveform having representative flow rates that vary from the representative flow rate for the reference period by less than a predetermined amount; and

defining the steady phase portion as including the reference period and the series of one or more consecutive qualifying periods.

4. A method for controlling breathing assistance provided to a patient, comprising:

providing breathing assistance to a patient according to one or more operational parameters;

estimating a leak flow by:

accessing data of a flow waveform indicating the flow of gas between the ventilation device and the patient;

identifying a steady phase portion near the end of an exhalation phase;

performing a linear regression of the identified portion of the flow waveform to determine an estimated leak flow in the breathing assistance system; and

controlling at least one of the operational parameters based at least on the estimated leak flow;

wherein identifying the steady phase portion comprises:

identifying a reference period of the flow waveform;

determining a representative flow rate for the reference period;

determining a series of one or more consecutive qualifying periods of the flow waveform having representative flow rates that vary from the representative flow rate for the reference period by less than a predetermined amount; and

defining the steady phase portion as including the reference period and the series of one or more consecutive qualifying periods.

5. A method according to claim 3 , wherein identifying the specific portion of the flow waveform further comprises identifying an end portion of an exhalation phase of the flow waveform.

6. A method according to claim 3 , wherein identifying the steady phase portion further comprises determining a portion of the flow waveform having a flow variation within a predetermined variation threshold.

7. A method according to claim 3 , wherein identifying the steady phase portion further comprises:

determining a first representative flow rate for a first portion of the flow waveform;

determining a second representative flow rate for a second portion of the flow waveform;

comparing the first representative flow rate with the second average flow rate; and

determining the steady phase portion based at least on the results of the comparison.

8. A method according to claim 3 , wherein identifying the steady phase portion comprises:

identifying a reference period of the flow waveform;

determining a representative flow rate for the reference period;

for each of a plurality of additional periods of the flow waveform:

determining a representative flow rate for the additional period;

comparing the representative flow rate for the additional period to the representative flow rate for the reference period; and

identifying the additional period as a qualifying additional period if the representative flow rate for the additional period varies from the representative flow rate for the reference period by less than a predetermined amount; and

defining the steady phase portion to include the reference period and each qualifying additional period.

9. A method according to claim 3 , further comprising:

determining whether an breath phase following the exhalation phase is a ventilator controlled inhalation or a patient-triggered inhalation; and

if the inhalation phase is a ventilator controlled inhalation, defining the end of the specific portion as the end of the exhalation phase; and

if the inhalation phase is a patient-triggered inhalation, defining the end of the specific portion as a predetermined time period before the end of the exhalation phase.

10. A method according to claim 3 , comprising determining as the estimated leak flow a flow value corresponding to the end of the exhalation phase based on the results of the linear regression.

11. A method according to claim 4 , wherein controlling at least one of the operational parameters based at least on the estimated leak flow comprises controlling at least one of a pressure and a gas flow rate based at least on the estimated leak flow.

12. A method according to claim 4 , further comprising displaying the estimated leak flow on a display device.

13. A method according to claim 4 , wherein identifying the steady phase portion comprises determining a portion of the flow waveform having a flow variation within a predetermined variation threshold.

14. A method according to claim 4 , wherein identifying the steady phase portion comprises:

determining a first representative flow rate for a first portion of the flow waveform;

determining a second representative flow rate for a second portion of the flow waveform;

comparing the first representative flow rate with the second average flow rate; and

determining the steady phase portion based at least on the results of the comparison.

15. A method according to claim 4 , wherein identifying the steady phase portion comprises:

identifying a reference period of the flow waveform;

determining a representative flow rate for the reference period;

for each of a plurality of additional periods of the flow waveform:

determining a representative flow rate for the additional period;

comparing the representative flow rate for the additional period to the representative flow rate for the reference period; and

identifying the additional period as a qualifying additional period if the representative flow rate for the additional period varies from the representative flow rate for the reference period by less than a predetermined amount; and

defining the steady phase portion to include the reference period and each qualifying additional period.

16. A breathing assistance system according to claim 1 , wherein the controller is further configured to control at least one of the operational parameters of the pneumatic system based at least on the estimated leak flow.

17. A breathing assistance system according to claim 1 , wherein identifying the specific portion of the flow waveform comprises determining a portion of the flow waveform having a flow variation within a predetermined variation threshold.