Method of measuring cardiac related parameters non-invasively via the lung during spontaneous and controlled ventilation

Abstract

An apparatus to measure pulmonary blood flow and cardiac output (Q) comprising: a) a breathing circuit which, at exhalation, keeps exhaled gas separate from inhaled gas and at inhalation, when V E is greater than first gas set (FGS) flow, results in a subject inhaling FGS first and then a second gas set (SGS), for the balance of inhalation; b) a gas sensor for monitoring gas concentrations at the patient-circuit interface; c) a gas flow control means for controlling the rate of FGS flow into the breathing circuit; d) machine intelligence consisting of a computer or logic circuit capable of controlling the gas flow control means which receives the output of the gas sensor means and outputs pulmonary blood flow.

1 - 61 . (canceled) 
     
     
         62 . A method of identifying the alveolar ventilation ({dot over (V)} A ), the method comprising:
 (1) using a breathing circuit characterized in that:
 i. on exhalation, exhaled gas is kept substantially separate from inhaled gas; 
 ii. on inhalation, when {dot over (V)} E  is less than FGS flow, the subject inhales FGS first and the balance of the minute ventilation is substantially SGS, 
 and: 
   (2) setting the FGS flow into the circuit at a rate greater than the subjects minute ventilation ({dot over (V)} E );   (3) measuring the end tidal CO 2  concentration (P ET CO 2 ) in a steady state   (4) progressively lowering the FGS flow into the circuit, either breath by breath or continuously, until after a time equal to the time of recirculation of CO 2  within the patient after a rise in P ET CO 2  above a threshold value is observed;   (5) deriving {dot over (V)} A  as the rate of FGS flow at a point of the intersection between two lines comprising:   a. the average P ET CO 2  in steady state; and   b. a line fit to the P ET CO 2  values after the rise begins until the recirculation time.