Adjustment of ventilator pressure-time profile to balance comfort and effectiveness

Abstract

The invention is a ventilator whose servo-controller adjusts the degree of support by adjusting the profile of the pressure waveform as well as the pressure modulation amplitude. As the servo-controller increases the degree of support by increasing the pressure modulation amplitude, it also generates a progressively more square, and therefore efficient, pressure waveform; when the servo-controller decreases the degree of support by decreasing the pressure modulation amplitude, it also generates a progressively more smooth and therefore comfortable pressure waveform.

1 . A pressure support ventilator comprising:
 a flow generator to generate a flow of gas at a pressure, the pressure being a function of at least a waveform, an amplitude, and a smoothness parameter; and   a processor configured to determine a measure of ventilation of the patient, and to automatically adjust the smoothness parameter within a preset range to servo-control the measure of ventilation to at least equal a target ventilation.   
     
     
         2 . The pressure support ventilator of  claim 1 , wherein the waveform is a function of time. 
     
     
         3 . The pressure support ventilator of  claim 1 , wherein the waveform is a function of phase in a respiratory cycle. 
     
     
         4 . The pressure support ventilator of  claim 1 , wherein the waveform is a function of time and phase in a respiratory cycle. 
     
     
         5 . The pressure support ventilator of  claim 1 , wherein the waveform approximates a waveform shape of eupneic transdiaphragmatic pressure versus phase curve. 
     
     
         6 . The pressure support ventilator of  claim 1 , wherein the pressure is a function of at least a first smoothness parameter and a second smoothness parameter. 
     
     
         7 . The pressure support ventilator of  claim 6 , wherein the first smoothness parameter is configured to servo-control the measure of ventilation during inspiration, and the second smoothness parameter is configured to servo-control the measure of ventilation during expiration. 
     
     
         8 . The pressure support ventilator of  claim 1 , wherein the first smoothness parameter is configured to servo-control the measure of ventilation during early inspiration and expiration, and the second smoothness parameter is configured to servo-control the measure of ventilation during late inspiration and expiration. 
     
     
         9 . The pressure support ventilator of  claim 1 , wherein the smoothness parameter is adjusted to generate a pressure waveform that progressively varies between a square profile and a smooth profile. 
     
     
         10 . The pressure support ventilator of  claim 9 , wherein when the smoothness parameter increases, the pressure waveform progressively becomes a more smooth and less square pressure waveform, and wherein when the smoothness parameter decreases, the pressure waveform progressively becomes a less smooth and more square pressure waveform. 
     
     
         11 . The pressure support ventilator of  claim 9 , wherein the pressure waveform includes a first, non-decreasing portion during inspiration and a second, non-increasing portion during expiration. 
     
     
         12 . The pressure support ventilator of  claim 11 , wherein when the smoothness parameter changes, the first, non-decreasing portion progressively varies between a raised cosine waveform and a rising step waveform, and the second, non-increasing portion progressively varies between a quasi-exponential decay waveform and a descending step waveform. 
     
     
         13 . The pressure support ventilator of  claim 1 , wherein the processor is further configured to automatically adjust the amplitude within a preset range to servo-control the measure of ventilation to at least equal the target ventilation. 
     
     
         14 . The pressure support ventilator of  claim 1 , wherein the smoothness parameter is controlled to be a function of the amplitude. 
     
     
         15 . The pressure support ventilator of  claim 1 , wherein the servo-control is performed firstly by increasing or decreasing the amplitude, and secondarily adjusting the smoothness parameter if the measure of ventilation remains below the target ventilation. 
     
     
         16 . The pressure support ventilator of  claim 1 , wherein when the measure of ventilation is inadequate, a degree of ventilatory support is increased by at least one of increasing the amplitude and decreasing the smoothness parameter, and when the measure of ventilation exceeds that required by the patient, the degree of ventilatory support is decreased by at least one of decreasing the amplitude and increasing the smoothness parameter. 
     
     
         17 . A pressure support ventilator comprising:
 means for delivering a controlled supply of breathable gas to a patient's airway at a pressure, the pressure being a function of at least a waveform, an amplitude and a smoothness parameter;   means for determining a measure of ventilation of the patient; and   means for automatically adjusting the smoothness parameter within a preset range to servo-control the measure of ventilation to at least equal a target ventilation.   
     
     
         18 . The pressure support ventilator of  claim 17 , wherein the waveform is a function of time. 
     
     
         19 . The pressure support ventilator of  claim 17 , wherein the waveform is a function of phase in a respiratory cycle. 
     
     
         20 . The pressure support ventilator of  claim 17 , wherein the means for automatically adjusting controls the smoothness parameter to generate a pressure waveform that progressively varies between a square profile and a smooth profile.