Metabolic gas exchange and noninvasive cardiac output monitor

A respiratory gas analyzer for measuring the metabolic activity or cardiac output of a subject, comprising:

• a respiratory connector operative to be supported in contact with a subject so as to pass inhaled and exhaled gasses as the subject breathes;
• means for connecting to a source of respiratory gasses;
• a bi-directional flow meter adapted to generate electrical signals as a function of the volume of gasses which pass through it in either direction;
• a pass-through carbon dioxide scrubber operative to absorb carbon dioxide from gasses which pass through it;
• a capnometer;
• a valve shiftable between a first configuration and a second configuration;
• conduits interconnecting said respiratory connector, said means for connecting to a source of respiratory gasses, said scrubber, said flow meter, said capnometer and said valve;
• computer means for receiving the outputs of the flow meter and the capnometer;
• means for controlling the position of the valve;
• said computer being connected to said means for controlling the valving so as to interconnect the components in either a first configuration in which, upon inhalation by a subject substantially the entire inhaled volume is passed from the source of respiratory gasses, through the flow meter to the subject and upon exhalation by a subject substantially all of the exhaled gasses are passed through the flow meter in a direction opposite to the inhaled gasses, or a second configuration in which upon inhalation by a subject only a fraction of the inhaled gasses are passed through the flow meter from the source of respiratory gasses, with the balance constituting previously exhaled gasses stored in said conduits, and upon exhalation by a subject only a fraction of the exhaled gasses are passed through the flow meter in a direction opposite to the inhaled gasses, the balance being stored in said conduits, whereby the computer may calculate the cardiac output of a subject based on the difference between the carbon dioxide content of the exhaled gasses between the time the valve is in the first configuration and the time the valve is in the second configuration and the difference in the end-tidal carbon dioxide content of the exhaled breath between the times the valves are in the first configuration and the valves are in the second configuration;
• and means operative at such time as said valve is in said first configuration, whereby upon exhalation by a subject, the exhaled gasses are passed first through the scrubber, then through the flow meter in a direction opposite to the inhaled gasses, whereby the computer may generate a signal proportional to the integral of the difference between the inhaled and exhaled gas volumes over a period of time to calculate a subject's metabolic rate.