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A medical ventilator system and method that triggers, cycles, or both based on patient effort, which is determined from cross-correlating patient flow and patient pressure. The medical ventilator is also controlled such that sensitivity to a patient initiated trigger increases as the expiratory phas

A medical ventilator system and method that triggers, cycles, or both based on patient effort, which is determined from cross-correlating patient flow and patient pressure. The medical ventilator is also controlled such that sensitivity to a patient initiated trigger increases as the expiratory phase of the breathing cycle progresses. The present invention also provides adaptive adjustment of cycling criteria to optimize the cycling operation.

대표청구항 ▼

What is claimed is: 1. A system for providing a flow of gas to a patient comprising: a pressure generating system adapted to provide a flow of gas responsive to a control signal; a patient circuit having a first end coupled to the pressure generating system and adapted to communicate the flow of ga

What is claimed is: 1. A system for providing a flow of gas to a patient comprising: a pressure generating system adapted to provide a flow of gas responsive to a control signal; a patient circuit having a first end coupled to the pressure generating system and adapted to communicate the flow of gas with an airway of a patient; a flow monitor operatively coupled to the pressure generating system or the patient circuit; a pressure monitor operatively coupled to the patient circuit; an exhaust assembly adapted to communicate gas from within the patient circuit to ambient atmosphere; and a controller that receives a first output from the flow monitor and a second output from the pressure monitor and outputs the control signal that controls the flow of gas delivered to the patient circuit by the pressure generating system and, hence, the flow of gas at a patient's airway, wherein the controller detects onset of an inspiratory phase of a patient's breathing cycle for triggering an inspiratory flow of gas based on such a patient's inspiratory effort, which is determined based on both a flow related parameter determined from the first output and a pressure related parameter determined from the second output. 2. The system according to claim 1, wherein the pressure generating system includes: a blower that receives a supply of gas from a gas source and provides the flow of gas; a flow controller associated with the blower to control a rate of the flow of gas responsive to the control signal. 3. The system according to claim 1, wherein the flow monitor is a flow sensor is disposed in the first end of the patient circuit. 4. The system according to claim 1, wherein the patient circuit is a two-limb circuit. 5. The system according to claim 1, wherein the exhaust assembly includes an exhaust flow controller to control a rate of the exhaust flow of gas from the patient circuit responsive to an exhaust flow control signal provided by the controller. 6. The system according to claim 1, further comprising a secondary gas flow system that delivers a secondary flow of gas to the patient circuit, wherein the secondary gas flow system includes: a conduit configured and arranged so as to communicate the secondary flow of gas from a source of the secondary flow of gas to the patient circuit; and a second flow monitor adapted to measure the secondary flow of gas in the conduit and to output a third output indicative thereof. 7. The system according to claim 1, wherein the controller establishes a trigger lockout interval, which is a period of time during each expiratory phase of a breathing cycle in which triggering the inspiratory flow of gas is prevented, based on the first output, the second output, or both. 8. The system according to claim 1, wherein the controller: determines a patient flow difference (Qpatient-Q ref) as the flow related parameter, where Qpatient is a current patient flow determined from the first output and Qref is a reference patient flow determined from the first output at a start of a trigger window, which is a period of time during which triggering the inspiratory flow of gas is permitted; determines a patient pressure difference(Pref-P patient) as the pressure related parameter, where Ppatient is a current patient pressure determined from the second output and P ref is a reference patient pressure determined from the second output at the start of the trigger window; determines the patient's inspiratory effort as a product of the patient flow difference and the patient pressure difference; and triggers the inspiratory flow of gas responsive to the patient's inspiratory effort exceeding a threshold. 9. The system according to claim 1, wherein the controller: determines a patient flow difference (Qpatient-Q ref) as the flow related parameter, where Qpatient is a current patient flow determined from the first output and Qref is a reference patient flow determined from the first output at a start of a trigger window, which is a period of time during which triggering the inspiratory flow of gas is permitted; determines a patient pressure difference (Pref-P patient) as the pressure related parameter, where Ppatient is a current patient pressure determined from the second output and P ref is a reference patient pressure determined from the second output at the start of the trigger window; determines the patient's inspiratory effort as a product of the patient flow difference and the patient pressure difference; sums the patient's inspiratory efforts accumulated over a time interval; and triggers the inspiratory flow of gas responsive to the sum of the patient's inspiratory efforts over the time interval exceeding a threshold. 10. The system according to claim 1, wherein the controller: determines a patient pressure difference (Pref-P patient) as the pressure related parameter, where Ppatient is a current patient pressure determined from the second output and P ref is a reference patient pressure determined from the second output at a start of a trigger window; delays the patient pressure difference in time to determine a delayed patient pressure difference; determining a current patient flow from the first output as the flow related parameter; determines a product of a current patient flow and the delayed patient pressure difference as the patient's inspiratory effort; sums the patient's inspiratory efforts accumulated over a time interval; and triggers the inspiratory flow of gas responsive to the sum of the patient's inspiratory effort exceeding a threshold. 11. The system according to claim 1, wherein the controller detects onset of an expiratory phase of a patient's breathing cycle for cycling from providing the inspiratory flow of gas to allowing an expiratory flow of gas from the exhaust assembly based on such a patient's expiratory effort, which is determined based on both the first output and the second output. 12. The system according to claim 11, wherein the controller: determines a patient flow difference (Qref-Q patient), where Qpatient is a current patient flow determined from the first output and Qref is a reference patient flow determined from the first output at a start of a cycling window, which is a period of time during which the expiratory flow of gas from the patient circuit is permitted; determines a patient pressure difference (Ppatient-Pref), where Ppatient is a current patient pressure determined from the second output and Pref is a reference patient pressure determined from the second output at the start of the cycling window; determines the patient's expiratory effort as a product of the patient flow difference and the patient pressure difference; and cycles from providing the inspiratory flow of gas to allowing an expiratory flow of gas from the exhaust assembly responsive to the patient's expiratory effort exceeding a threshold. 13. The system according to claim 11, wherein the controller: determines a patient pressure difference (Ppatient-Pref,), where Ppatient is a current patient pressure determined from the second output and Pref is a reference patient pressure determined from the second output at a start of a cycling window, which is a period of time during which the expiratory flow of gas from the patient circuit is permitted; delays a patient flow determined from the first output to determine a delayed patient flow; determines a product of the patient pressure difference and the delayed patient flow as the patient's expiratory effort; sums the patient's expiratory efforts accumulated over a time interval; and cycles from providing the inspiratory flow of gas to allowing an expiratory flow of gas from the exhaust assembly responsive to the sum of the patient's expiratory effort exceeding a threshold. 14. The system according to claim 11, wherein the controller: determines a patient flow difference (Qref-Q patient ), where Qpatient is a current patient flow determined from the first output and Qref is a reference patient flow determined from the first output at a start of a cycling window, which is a period of time during which the expiratory flow of gas from the patient circuit is permitted; determines a patient pressure difference (Ppatient-Pref), where Ppatient is a current patient pressure determined from the second output and Pref is a reference patient pressure determined from the second output at the start of the cycling window; determines the patient's expiratory effort as a product of the patient flow difference and the patient pressure difference; sums the patient's expiratory efforts accumulated over a time interval; and cycles from providing the inspiratory flow of gas to allowing an expiratory flow of gas from the exhaust assembly responsive to the sum of the patient's expiratory efforts over the time interval exceeding a threshold. 15. The system according to claim 1, wherein the controller cycles from providing the inspiratory flow of gas to allowing an expiratory flow of gas from the exhaust assembly by comparing patient flow determined from the first output against a cycle threshold flow and cycles responsive to the patient flow falling below the cycle threshold flow. 16. The system according to claim 15, wherein the controller: monitors patient pressure, via the second output, at an end portion of an inspiratory phase and monitors patient flow, via the first output, at a beginning portion of an expiratory phase to determine whether the system cycled too early or too late; and adjusts the cycle threshold flow for a next breathing cycle responsive to a determination that the system cycled too early or too late. 17. A method of providing a flow of gas to a patient comprising: generating a flow of gas; providing the flow of gas to a patient via a patient circuit; controlling the flow of gas delivered to a patient responsive to a control signal; monitoring the flow of gas in the patient circuit and outputting a first flow signal indicative thereof; monitoring a pressure of the flow of gas in the patient circuit and outputting a first pressure signal indicative thereof; communicating gas from within the patient circuit to ambient atmosphere; and detecting onset of an inspiratory phase of a patient's breathing cycle for triggering an inspiratory flow of gas based on such a patient's inspiratory effort, which is determined based on both a flow related parameter determined from the first flow signal and a pressure related parameter determined from the first pressure signal. 18. The method according to claim 17, wherein detecting the onset of the inspiratory phase includes: determining a patient flow difference (Qpatient-Q ref) as the flow related parameter, where Qpatient is a current patient flow determined from the first flow signal and Qref is a reference patient flow determined from the first flow signal at a start of a trigger window, which is a period of time during which the expiratory flow of gas is permitted; determining a patient pressure difference (Pref-P patient) as the pressure related parameter, where Ppatient is a current patient pressure determined from the first pressure signal and Pref is a reference patient pressure determined from the first pressure signal at the start of the trigger window; and determining the patient's inspiratory effort as a product of the patient flow difference and the pressure difference. 19. The method according to claim 18, further comprising triggering an inspiratory flow of gas responsive to the patient's inspiratory effort exceeding a threshold. 20. The method according to claim 17, wherein detecting the onset of the inspiratory phase includes: determining a patient flow difference (Qpatient-Q ref) as the flow related parameter, where Qpatient is a current patient flow determined from the first flow signal and Qref is a reference patient flow determined from the first flow signal at a start of a trigger window, which is a period of time during which the expiratory flow of gas is permitted; determining a patient pressure difference (Pref-P patient) as the pressure related parameter, where Ppatient is a current patient pressure determined from the first pressure signal and Pref is a reference patient pressure determined from the first pressure signal at a start of a trigger window; determining the patient's inspiratory effort as a product of a patient flow difference and the pressure difference; summing the patient's inspiratory efforts accumulated over a time interval; and triggering an inspiratory flow of gas responsive to the sum of the patient's inspiratory efforts over the time interval exceeding a threshold. 21. The method according to claim 17, wherein detecting the onset of the inspiratory phase includes: determining a patient pressure difference (Pref-P patient) as the pressure related parameter, where Ppatient is a current patient pressure determined from the first pressure signal and Pref is a reference patient pressure determined from the first pressure signal at a start of a trigger window, which is a period of time during which the expiratory flow of gas is permitted; determining a delayed patient pressure difference, where a length of the delay is selected so as to account for an inherent physiological delay between an onset of a pressure drop and a rise in patient flow occurring at a beginning of inspiration; determining a current patient flow from the first flow signal as the flow related parameter; determining a product of the current patient flow and the delayed patient pressure difference as the patient's inspiratory effort; summing the patient's inspiratory efforts accumulated over a time interval; and triggering an inspiratory flow of gas responsive to the sum of the patient's inspiratory effort exceeding a threshold. 22. The method according to claim 17, further comprising detecting onset of an expiratory phase of a patient's breathing cycle for cycling from providing an inspiratory flow of gas to allowing an expiratory flow of gas from the patient circuit based on such a patient's expiratory effort, wherein detecting the onset of an expiratory phase is determined based on both the first flow signal and the first pressure signal. 23. The method according to claim 22, wherein detecting an onset of an expiratory phase includes: determining a patient flow difference (Qref-Q patient), where Qpatient is a current patient flow determined from the first flow signal and Qref is a reference patient flow determined from the first flow signal at a start of a cycling window, which is a period of time during which the expiratory flow of gas from the patient circuit is permitted; determining a patient pressure difference (Ppatient-Pref), where Ppatient is a current patient pressure determined from the first pressure signal and Pref is a reference patient pressure determined from the first pressure signal at the start of the cycling window; determining the patient's expiratory effort as a product of the patient flow difference and the patient pressure difference; and cycling from providing an inspiratory flow of gas to allowing an expiratory flow of gas from the patient circuit responsive to the patient's expiratory effort exceeding a threshold. 24. The method according to claim 22, wherein detecting an onset of an expiratory phase includes: determining a patient pressure difference (Ppatient-Pref,), where Ppatient is a current patient pressure determined from the first pressure signal and Pref is a reference patient pressure determined from the first pressure signal at a start of a cycling window, which is a period of time during which the expiratory flow of gas from the patient circuit is permitted; delaying a patient flow from the first flow signal to determine a delayed patient flow; determining a product of the patient pressure difference and the delayed patient flow as the patient's expiratory effort; summing the patient's expiratory efforts accumulated over a time interval; and cycling from providing an inspiratory flow of gas to allowing an expiratory flow of gas from the patient circuit responsive to the sum of the patient's expiratory effort exceeding a threshold. 25. The method according to claim 22, wherein detecting an onset of an expiratory phase includes: determining a patient flow difference (Qref-Q patient), where Qpatient is a current patient flow determined from the first flow signal and Qref is a reference patient flow determined from the first flow signal at a start of a cycling window, which is a period of time during which the expiratory flow of gas from the patient circuit is permitted; determining a patient pressure difference (Ppatient-Pref,), where Ppatient is a current patient pressure determined from the first pressure signal and Pref is a reference patient pressure determined from the first pressure signal at the start of the cycling window; determining the patient's expiratory effort as a product of the patient flow difference and the patient pressure difference; summing the patient's expiratory efforts accumulated over a time interval; and cycling from providing an inspiratory flow of gas to allowing an expiratory flow of gas from the patient circuit responsive to the sum of the patient's expiratory efforts over the time interval exceeding a threshold. 26. The method according to claim 17, wherein the controller cycles from providing an inspiratory flow of gas to allowing an expiratory flow of gas from the patient circuit by comparing patient flow determined from the first flow signal against a cycle threshold flow and cycles responsive to the patient flow falling below the cycle threshold flow. 27. The method according to claim 26, further comprising: monitoring patient pressure, via the first pressure signal, at an end portion of an inspiratory phase; monitoring patient flow, via the first flow signal, at a beginning portion of an expiratory phase; determining whether cycling occurred too late based on the patient pressure at the end portion of the inspiratory phase; determining whether cycling occurred too early based on the patient flow at the beginning portion of the expiratory phase; and adjusting the cycle threshold flow for a next breathing cycle responsive to a determination that cycling occurred too early or too late. 28. A system for providing a flow of gas to a patient comprising: gas flow generating means for generating a flow of gas; flow communicating means for communicating the flow of gas to a patient; flow controlling means for controlling the flow of gas delivered to such a patient; flow monitoring means for monitoring a rate of the flow of gas; pressure monitoring means for monitoring a pressure of the flow of gas; exhausting means for communicating gas from the flow delivering means to ambient atmosphere; and processing means for detecting onset of an inspiratory phase of a patient's breathing cycle for triggering an inspiratory flow of gas based on such a patient's inspiratory effort, which is determined based on both (1) a flow related parameter determined from an output of the flow monitoring means and (2) a pressure related parameter determined from an output of the pressure monitoring means. 29. The system according to claim 28, wherein the gas flow generating means includes: a blower that receives a supply of gas from a gas source and provides the flow of gas; a flow controller associated with the blower to control a rate of the flow of gas responsive to the control signal. 30. The system according to claim 28, wherein the flow monitoring means is a flow sensor associated with the flow communicating means. 31. The system according to claim 28, wherein the flow communicating means is a two-limb patient circuit. 32. The system according to claim 28, wherein the exhausting means includes an exhaust flow controller to control a rate of the exhaust flow of gas from the flow communicating means responsive to an exhaust flow control signal provided by the processing means. 33. The system according to claim 28, further comprising a secondary gas flow delivery means for delivering a secondary flow of gas to the flow communicating means. 34. The system according to claim 28, wherein the processing means establishes a trigger lockout interval, which is a period of time during each expiratory phase of a breathing cycle in which triggering the inspiratory flow of gas is prevented, based on the output of the flow monitoring means, the output of the pressure monitoring means, or both. 35. The system according to claim 28, wherein the processing means detects onset of an expiratory phase of a patient's breathing cycle for cycling from providing the inspiratory flow of gas to allowing an expiratory flow of gas from the exhaust assembly based on such a patient's expiratory effort, which is determined based on the output of the flow monitoring means, the output of the pressure monitoring means, or both.