Ventilator patient monitor

Claim 3

The method according to claim 1 wherein the step of developing said accurate expiration signal comprises: a. generating a gas flow-rate signal from the gas flow received by said ventilator monitor; b. generating a mouth pressure signal from the gas pressure within the mouth of said patient; and c. processing said gas flow-rate signal and said mouth pressure signal to determine the time of exhalation of the patient.

Claim 6

The method according to claim 3 wherein the step of generating said expiration valve gas pressure signal includes the steps of: a. generating a real-time mouth pressure signal from the mouth pressure of the patient; b. generating an end of patient expiration mouth pressure signal from said real-time mouth pressure signal; and c. subtracting said end of patient expiration mouth pressure signal obtained at the end of a previous expiration from said real-time mouth pressure signal to form a difference signal representing a real-time estimate of the gas pressure across the expiration valve.

Claim 7

The method according to claim 4 wherein the step of generating said end of expiration mouth pressure signal includes the steps of: a. generating a logical first-estimate expiration pulse train from said gas flow-rate signal that assumes a third predetermined state during a first estimate of the expiration time of the patient, and a fourth predetermined state at all other times; b. threshold detecting said gas flow-rate signal at a preselected minimum level to produce a threshold signal having a fifth predetermined value when the flow-rate signal is below said minimum level and being representative of the flow-rate signal when said minimum level is exceeded, said preselected minimum level being representative of the gas flow-rate from the patient when expiration starts and ends; and c. tracking said real-time mouth pressure signal, during the time period when both said first-estimate expiration signal is in the third predetermined state and said gas flow-rate signal exceeds said preselected minimum level, to produce said end of expiration mouth pressure signal.

Claim 8

The method according to claim 3, wherein the step of comparing said gas pressure signal and said product signals to generate said logical comparison signal further includes generating an accurate expiration signal to control the gating of said flow-rate signal, the generating of said accurate expiration signal including the steps of: a. generating a flow-rate threshold signal from said flow-rate signal with said first predetermined state if the flow-rate signal is below a preselected signal level and said second predetermined state when the flow-rate signal exceeds the preselected signal level, said preselected signal level being representative of a minimum gas flow-rate defining expiration; b. generating an expiration valve pressure threshold signal from said difference signal with said first predetermined state if the difference signal is below a preselected signal level and said second predetermined state when the difference signal exceeds the said preselected signal level, said preselected level being representative of a minimum expiration valve pressure defining expiration; and c. gating the flow-rate threshold signal, the pressure threshold signal, and said logical comparison signal to generate said accurate expiration signal having said first and second predetermined states, the state of the accurate expiration signal being said second predetermined state when said pressure and flow-rate threshold signals are simultaneously in said first predetermined state, and the reciprocal of said logical comparison signal at all other times to include within the expiration time the time when said flow-rate and said difference signal levels are simultaneously below the preselected threshold levels.

Claim 9

A ventilator monitoring system responsive to the mouth pressure of a patient and the gas flow through an expiration valve to measure the gas volume expired by the patient by eliminating the inclusion of the measured volume of the gas flow through a leaking expiration valve during inspiration of the patient from the total measured volume of the monitored gas flow from the expiration valve, said system comprising: first means coupled to the mouth of the patient for detecting gas pressure within the mouth and generating a mouth pressure signal; second means coupled to an output port of said expiration valve for measuring the gas flow through said valve and for generating a gas flow-rate signal and a first-estimate expiration signal; third means responsive to said mouth pressure signal, said gas flow-rate signal, and said first-estimate expiration signal for generating an accurate expiration signal that defines the time period that the patient is expiring gas from his lungs; and fourth means responsive to said accurate expiration signal for gating said gas flow-rate signal to permit integration of a portion of the flow-rate signal to provide a measure of the patient expired gas volume, said gating being operable to eliminate the inclusion of that portion of the flow-rate signal corresponding to the inspiratory gas leaking through the expiration valve from the gas flow-rate signal that corresponds to the expiratory gas from the patient, thereby to limit the gas volume value obtained by integration to the volume of gas expired by the patient.

Claim 10

A ventilator monitoring system responsive to the mouth pressure of a patient and the gas flow through an expiration valve to measure the gas volume expired by the patient by eliminating the inclusion of the measured volume of the gas flow through a leaking expiration valve during inspiration of the patient from the total measured volume of the monitored gas flow from the expiration valve, said system comprising: first means coupled to the mouth of the patient for detecting gas pressure within the mouth and generating a mouth pressure signal; second means coupled to an output port of said expiration valve for measuring the gas flow through said valve and for generating a gas flow-rate signal and a first-estimate expiration signal; third means responsive to said mouth pressure signal, said gas flow-rate signal, and said first-estimate expiration signal for generating an accurate expiration signal that defines the time period that the patient is expiring gas from his lungs; and fourth means responsive to said accurate expiration signal for gating said gas flow-rate signal to permit integration of a portion of the flow-rate signal to provide a measure of the patient expired gas volume, said gating being operable to eliminate the inclusion of that portion of the flow-rate signal corresponding to the inspiratory gas leaking through the expiration valve from the gas flow-rate signal that corresponds to the expiratory gas from the patient, thereby to limit the gas volume value obtained by integration to the volume of gas expired by the patient.

Claim 11

The ventilator monitoring apparatus as in claim 7 wherein said first means comprises: a pressure transducer coupled to the mouth of the patient; and means for amplifying the output of said pressure transducer to provide a mouth pressure signal that varies linearly with the mouth pressure of the patient.

Claim 12

The ventilator monitoring apparatus as in claim 7 wherein said second means comprises gas flow-rate detection means coupled to the output port of the expiration valve, said gas flow-rate detection means having an output signal that is linearly related to the gas flow-rate through the expiration valve.

Claim 13

The ventilator monitoring apparatus as in claim 7 wherein said third means comprises: valve pressure estimation means responsive to said analog mouth pressure signal, said analog gas flow-rate signal, and said first estimate expiration signal for generating a signal representative of the pressure across the expiration valve; valve condition indicating means responsive to said valve pressure estimation means and said gas flow-rate signal for generating a logical signal having a first predetermined state defining an open valve, and a second predetermined state defining a closed valve; a low valve pressure voltage threshold circuit coupled to the output of the valve pressure estimation means to provide a logical indication of the first predetermined state when the signal representing the valve pressure falls below a preset level, and the second predetermined state when the signal representing the valve pressure exceeds the preset level, said preset level being representative of a valve pressure threshold value that defines a valve pressure error level; a low valve flow-rate voltage threshold circuit coupled to the gas flow-rate signal to provide a logical indication of the first predetermined state when the signal representing the gas flow-rate falls below a preset level, and the second predetermined state when the gas flow-rate signal exceeds the last-named preset level, said last-named preset level being representative of a gas flow-rate threshold value that defines a gas flow-rate error level; and gating circuit means responsive to inputs from the valve condition indicating means, the low valve pressure voltage threshold circuit, and the low valve flow-rate voltage threshold circuit for generating said accurate expiration signal having said first and second predetermined states, the state of the accurate expiration signal being said second predetermined state when said pressure and flow-rate threshold circuits are simultaneously in said first predetermined state, and the reciprocal of the output of said valve condition indicating means at all other times to include within the expiration time the time when said valve pressure and flow-rate signal levels are simultaneously below the preset threshold levels.

Claim 14

The ventilator monitoring apparatus as in claim 10 wherein said valve condition indicating means comprises: an amplifier circuit coupled to said analog gas flow-rate signal with gain equivalent to a preselected value to obtain an output signal that is proportional to the product of the expiration valve flow-rate and the preselected value, said preselected value being representative of an expiration valve resistance threshold value that defines an open versus a closed expiration valve; and a comparator circuit responsive to the generated expiration valve pressure signal and said valve flow-threshold resistance product signal to provide a logical signal having said first predetermined state if the actual valve resistance is less than said preselected threshold resistance, and said second predetermined state if the actual valve resistance exceeds the preselected threshold resistance.

Claim 15

The ventilator monitoring apparatus as in claim 10 wherein said valve condition indicating means comprises: first amplifier circuit coupled to said analog gas flow-rate signal with gain equivalent to a first preselected value to obtain an output signal that is proportional to the product of the expiration valve flow-rate and the first preselected value, said first preselected value being representative of a minimum expiration valve resistance threshold value that defines an open versus a closed expiration valve; a second amplifier circuit coupled to said analog gas flow-rate signal with a gain equivalent to a second preselected value to obtain an output signal that is proportional to the product of the expiration valve flow-rate and the second preselected value, said second preselected value being representative of a maximum expiration valve resistance threshold value that defines an open versus a closed expiration valve; a first comparator circuit responsive to said expiration valve pressure signal and the output signal of said first amplifier circuit to provide a first logical signal having said first predetermined state if the actual valve resistance is less than said first preselected threshold resistance, and said second predetermined state if the actual valve resistance exceeds said first preselected threshold resistance; a second comparator circuit responsive to said expiration valve pressure signal and the output signal of said second amplifier circuit to provide a second logical signal having said first predetermined state if the actual valve resistance is less than said second preselected threshold resistance, and said second predetermined state if the actual valve resistance exceeds said second preselected threshold resistance; an inverter circuit responsive to the output of said first comparator circuit; and a flip-flop circuit responsive to the outputs of said inverter circuit and said second comparator circuit to provide an output signal assuming said second predetermined state after the increasing actual valve resistance crosses the second preselected threshold resistance, and the first predetermined state after the decreasing actual valve resistance crosses said first preselected threshold resistance.

Claim 16

The ventilator monitoring apparatus as in claim 7 wherein said fourth means comprises: a gate circuit responsive to said accurate expiration signal and coupled to said scond means to block transmission of that portion of said gas flow-rate signal that is representative of the gas flow that leaks through the expiration valve during patient inspiration; and patient expired gas volume accumulation means coupled to said gate circuit for integrating a gated gas flow-rate signal to provide an expired gas volume signal representative of the volume of gas expired by the patient.