Method and device for monitoring and improving patient-ventilator interaction
First Claim
1. A method for detecting the onset of inspiratory effort (Tonset) in a patient on mechanical ventilation, comprising the steps of:
- (a) monitoring airway pressure, rate of gas flow, and volume of gas flow of the patient;
(b) applying a gain factor (Kf) to the signal representing rate of gas flow to convert the gas flow signal into a gas flow pressure signal;
(c) applying a gain factor (Kv) to the signal representing volume of gas flow, also to convert the gas volume signal into a gas volume pressure signal;
(d) generating a composite pressure signal comprising the sum of airway pressure signal, gas flow pressure signal, and gas volume pressure signal, with all signals having suitably adjusted polarity;
(e) adjusting Kf and Kv to result in a desired linear trajectory of composite pressure signal baseline in the latter part of the exhalation phase;
(f) comparing (i) current composite pressure signal values with selected earlier composite pressure signal values, and/or (ii) current composite pressure signal values with values expected at current time based on extrapolation of composite pressure signal trajectory at specified earlier times, and/or (iii) the current rate of change in the composite pressure signal with a selected earlier rate of change in the composite pressure signal;
(g) comparing differences obtained from such comparison(s) made in step (f) with selected threshold values; and
(h) identifying Tonset when at least one of said differences exceeds said threshold values.
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Abstract
Method and apparatus for non-invasively determining the time onset (Tonset) and end (Tend) of patient inspiratory efforts. A composite pressure signal is generated comprising the sum of an airway pressure signal, a gas flow pressure signal obtained by applying a gain factor (Kf) to a signal representing gas flow rate and a gas volume pressure signal obtained by applying a gain factor (Kv) to a signal representing volume of gas flow. Kf and Kv values are adjusted to result in a desired linear trajectory of composite pressure signal baseline in the latter part of the exhalation phase. The current composite pressure signal is compared with (i) selected earlier composite pressure signal values and/or (ii) value expected at current time based on extrapolation of composite pressure signal trajectory at specified earlier times and/or (iii) the current rate of change in the composite pressure signal with a selected earlier rates of change. The differences obtained by the comparison are compared with selected threshold values. Tonset is identified when at least one of the differences exceeds the threshold values.
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Citations
46 Claims
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1. A method for detecting the onset of inspiratory effort (Tonset) in a patient on mechanical ventilation, comprising the steps of:
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(a) monitoring airway pressure, rate of gas flow, and volume of gas flow of the patient;
(b) applying a gain factor (Kf) to the signal representing rate of gas flow to convert the gas flow signal into a gas flow pressure signal;
(c) applying a gain factor (Kv) to the signal representing volume of gas flow, also to convert the gas volume signal into a gas volume pressure signal;
(d) generating a composite pressure signal comprising the sum of airway pressure signal, gas flow pressure signal, and gas volume pressure signal, with all signals having suitably adjusted polarity;
(e) adjusting Kf and Kv to result in a desired linear trajectory of composite pressure signal baseline in the latter part of the exhalation phase;
(f) comparing (i) current composite pressure signal values with selected earlier composite pressure signal values, and/or (ii) current composite pressure signal values with values expected at current time based on extrapolation of composite pressure signal trajectory at specified earlier times, and/or (iii) the current rate of change in the composite pressure signal with a selected earlier rate of change in the composite pressure signal;
(g) comparing differences obtained from such comparison(s) made in step (f) with selected threshold values; and
(h) identifying Tonset when at least one of said differences exceeds said threshold values. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 18, 23)
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15. A method for detecting the onset of inspiratory effort (Tonset) in a patient on mechanical ventilation, comprising the steps of:
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(a) monitoring airway pressure and rate of gas flow of the patient;
(b) applying a gain factor (Kf) to the signal representing rate of gas flow to covert the gas flow signal into a gas flow pressure signal;
(c) generating a composite pressure signal comprising the sum of airway pressure signal and the gas flow pressure signal, with the two signals having suitably adjusted polarity;
(d) comparing (i) the current composite pressure signal values with values expected based on extrapolation of composite pressure signal trajectory at specified earlier times, and/or (ii) the current rate of change of composite pressure signal with a selected earlier rate of change of composite pressure signal;
(e) comparing differences obtained from such comparison(s) made in step (d) with selected threshold values; and
(f) identifying Tonset when at least one of said differences exceeds said threshold values. - View Dependent Claims (16, 17, 19)
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20. A method for cycling off the inflation phase of a mechanical ventilator comprising:
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measuring the average interval between patient inspiratory efforts in a patient in a suitable number of elapsed breaths (TTOT) with said average being updated at suitable intervals;
identifying onset of current inspiratory effort;
monitoring time from said onset of inspiratory effort; and
generating a signal that causes the ventilator to cycle off when time elapsed since onset of inspiratory effort exceeds a specified fraction of TTOT. - View Dependent Claims (21)
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22. A method for cycling off the inflation phase of a ventilator in pressure support ventilation comprising:
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measuring the interval between successive inspiratory efforts in a suitable number of elapsed breaths (TTOT);
measuring inspiratory flow rate at specified times in those elapsed breaths which triggered ventilator cycles, said specified times corresponding to a specified fraction of the TTOT, measured from the onset of inspiratory effort of said each breath or from the trigger time of the ventilator;
calculating the average of the flow values obtained at said specified times in said elapsed breaths; and
generating a signal that causes the ventilator to cycle off when inspiratory flow in the current inflation phase decreases below said average flow value.
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24. A device for detecting the onset of inspiratory effort (Tonset) in a patient on mechanical ventilation, comprising:
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circuitry for measuring airway pressure, rate of gas flow and volume of gas flow of the patient;
amplifier to apply a gain factor (Kf) to the signal representing rate of gas flow to convert said signal into a gas flow pressure signal;
amplifier to apply a gain factor (Kv) to the signal representing volume of gas flow to convert said signal into a gas volume pressure signal;
summing amplifier that generates a composite pressure signal comprising the sum of airway pressure signal, the gas flow pressure signal, and the gas volume pressure signal, with all signals having suitably adjusted polarity;
means to permit adjustment of Kf and Kv to provide a desired trajectory of composite pressure signal baseline in the latter part of the exhalation phase;
circuitry to direct said composite pressure signal to a Tonset identification circuitry during a suitable period in the expiratory phase, said identification circuitry comprising circuitry to detect a change in trajectory; and
means for generating a signal corresponding to Tonset when measured change in trajectory of composite pressure signal exceeds a specified threshold. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 44, 45, 46)
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38. A device for estimating a desirable duration of inflation phase of a ventilator, comprising:
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circuitry to identify inspiratory efforts of a patient;
means to calculate the time difference between patient inspiratory efforts (patient TTOT);
means for displaying a value corresponding to a specified fraction of patient TTOT, said specified fraction being a user input or a default value between 0.3 and 0.5. - View Dependent Claims (39, 40, 41)
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42. A device for determining the desirable inspiratory flow threshold for terminating inflation cycles in the pressure support ventilation mode comprising:
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circuitry for estimating desirable duration of inflation phase of the ventilator;
means to measure inspiratory flow in recently elapsed breaths after said desirable duration has elapsed from the ventilator'"'"'s trigger time, or from the onset of inspiratory effort preceding triggered breaths, or from a specified point in between the latter two points; and
means for displaying the value of said measured flow. - View Dependent Claims (43)
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Specification