Metabolic gas exchange and noninvasive cardiac output monitor

• US 6,135,107 A
• Filed: 11/13/1998
• Issued: 10/24/2000
• Est. Priority Date: 03/11/1996
• Status: Expired due to Fees

• Current Assignee: Microlife Medical Home Solutions Inc.
• Original Assignee: James R. Mault
• Inventors: Mault, James R.
• Primary Examiner(s): Weiss, John G.
• Assistant Examiner(s): SRIVASTAVA, VIRENDRA KUMAR
• Application Number:
  US09/191,782
• Time in Patent Office: 711 Days
• Field of Search: 128/204.22, 128/204.23, 128/205.27, 128/205.23, 600/532, 600/529, 600/531
• US Class Current: 128/204.23
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence
• CPC Class Codes: A61B 5/0836 Measuring rate of CO2 production
• CPC Class Codes: A61M 15/00 Inhalators drug delivery in endotracheal tubes A61M16/04

Abstract

A respiratory gas analyzer for measuring the metabolic activity and the cardiac output of a subject includes a bi-directional flow meter and a capnometer sensor interconnected by conduits and valving between a mouthpiece and a source of respiratory gasses which may be a controlled source or the atmosphere. A pass-through carbon dioxide scrubber may be plugged into the conduits and the valving controlled so that upon inhalation by the subject gasses are passed through the flow meter to the mouthpiece and upon exhalation the exhaled gasses are passed first through the scrubber and then through the flow meter in a direction opposite to the inhaled gasses. A computer connected to receive the signals from the flow meter and the capnometer can then calculate the subject'"'"'s metabolic activity. When the valving is shifted a portion of the exhaled gasses are stored in the conduit so that upon inhalation the subject inhales a substantial portion of rebreathed gasses. The computer can then calculate the patient'"'"'s cardiac output as a function of the changes in total carbon dioxide content of the exhaled gas before and after the valve is shifted from a direct input to a rebreathed position and the difference in end-tidal carbon dioxide between these two positions. The carbon dioxide scrubber may be removed from the circuitry during calculation of cardiac output to conserve the scrubber life.

Claims

1. 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 flow meter adapted to generate electrical signals as a function of the volume of gasses which pass through it;

a respiratory gas analyzer;

a valve shiftable between a first configuration and a second configuration;

means for controlling the position of the valve;

conduits interconnecting said respiratory connector, said means for connecting to a source of respiratory gasses, said flow meter and said respiratory gas analyzer;

a computer for receiving the outputs of the flow meter and the respiratory gas analyzer;

said computer being operative to determine the carbon dioxide content of the gasses flowing through said respiratory gas analyzer and being connected to said means for controlling the position of the valve 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, to the subject through the respiratory connector and upon exhalation by a subject substantially all of the exhaled gasses are passed through the flow meter and the respiratory gas analyzer, or a second configuration in which upon inhalation by a subject only a fraction of the gasses passes through the respiratory connector are derived from said source of respiratory gasses, with the balance of the gasses passed through the respiratory connector constituting previously exhaled gasses, whereby the computer may calculate the cardiac output of a subject based on the difference between the carbon dioxide content and the end-tidal carbon dioxide content of the exhaled gasses between the times the valve is in the first configuration and the valve is in the second configuration and the computer may calculate a subject'"'"'s metabolic activity based on the outputs of the flow meter and respiratory gas analyzer when the valve is in the first position.