Metabolic gas exchange and noninvasive cardiac output monitor

• US 5,836,300 A
• Filed: 03/11/1997
• Issued: 11/17/1998
• Est. Priority Date: 03/11/1996
• Status: Expired due to Term

• Current Assignee: Microlife Medical Home Solutions Inc.
• Original Assignee: James R. Mault
• Inventors: Mault, James R.
• Primary Examiner(s): Yu, Mickey
• Assistant Examiner(s): SRIVASTAVA, VIRENDRA KUMAR
• Application Number:
  US08/814,677
• Time in Patent Office: 616 Days
• Field of Search: 128/204.22, 128/204.23, 600/532, 600/529, 600/531, 600/538, 600/484
• 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 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.

2. The metabolic gas analyzer of claim 1 wherein the scrubber may be connected to the conduits so that 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, or the scrubber may be removed from the conduit so that upon exhalation by a subject exhaled gasses passing through the flow meter in a direction opposite to the inhaled gasses are not first passed through the scrubber.

3. A respiratory gas analyzer useful for calculating the respiratory oxygen consumption per unit time or the cardiac output of a subject, comprising:

a respiratory connector operative to be supported in contact with the mouth of a subject so as to pass inhaled and exhaled gasses as the subject breathes;

means for connecting to a source of respiratory gasses;

a pass-through 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 computer for receiving generated electrical signals from the flow meter and the capnometer;

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

a connector for removably attaching the scrubber to the conduits; and

valve means connected to the conduits for arranging the respiratory gas analyzer in either a first configuration in which, upon inhalation by a subject gasses are passed from the source of respiratory gasses through the flow meter to a subject so that substantially all of the inhaled gasses are passed through the flow meter or a second configuration wherein upon inhalation by a subject a portion of the inhaled gasses are derived from previously exhaled gas stored within the conduits and the balance is derived from the source of respiratory gasses through the flow meter, the computer being operative to calculate an electrical signal which is a function of the cardiac output of a subject based upon the difference in the carbon dioxide content in the expired gasses between the time that the valve is in the first configuration and the valve is in the second configuration, and the difference between the end-tidal carbon dioxide content of the exhaled breath between the times that the valve is in said first configuration and the time that the valve is in said second configuration; and

means for connecting said scrubber to the conduits when said valve is in said first configuration, so that exhaled gasses are passed first through the scrubber, then through the flow meter in a direction opposite to the inhaled gasses, whereby the flow meter is operative to generate a signal proportional to the integral of the difference between the inhaled and exhaled gas volumes over a period of time to calculate the metabolic activity of a subject.

4. The respiratory gas analyzer of claim 3 in which the source of respiratory gasses is the atmosphere.

5. The respiratory gas analyzer of claim 3 in which said portion of inhaled gasses which are derived from the previously exhaled gasses represents about 10-60% of the entire inhaled gas.