Respiratory gas analyzer including a carbon dioxide and respiratory quotient computer

• US 3,895,630 A
• Filed: 06/21/1974
• Issued: 07/22/1975
• Est. Priority Date: 06/04/1973
• Status: Expired due to Term

• Current Assignee: John A. Bachman
• Original Assignee: John A. Bachman
• Inventors: Bachman, John A.
• Primary Examiner(s): Gaudet, Richard A.
• Assistant Examiner(s): Cohen, Lee S.
• Application Number:
  US05/481,517
• Time in Patent Office: 396 Days
• Field of Search: 128/2.07,2.08 73/421.5R,23R,27R,195 23/254E,255E
• US Class Current: 600/531
• CPC Class Codes: A61B 5/083 Measuring rate of metabolism by using breath test, e.g. measuring rate of oxygen consumption

Abstract

A respiratory gas analyzer system and apparatus for medical purposes is provided. The system includes a thermal conductivity cell for measuring the amount of carbon dioxide in a sample of a subject'"'"''"'"'s expired air. The system also includes a computer which periodically calculates and provides a digital display of the carbon dioxide production in the expired air. The latter computer also calculates and digitally displays the ratio of carbon dioxide production to oxygen depletion in the expired air, which is known as the '"'"''"'"''"'"''"'"'respiratory quotient'"'"''"'"''"'"''"'"'.

Claims

1. Apparatus for automatically periodically measuring the volume of air expired by a subject during each of a succession of given time intervals, and for measuring and computing the carbon dioxide production in the expired air for each of the time intervals, said apparatus including:

metering means for receiving the expired air from the subject and for generating electrical output pulses having a repetition frequency representative of the volume of air expired by the subject during successive time intervals and under standard temperature conditions;

volume computer means including multiplier circuit means coupled to said metering means for multiplying each pulse of the electrical output pulses therefrom by a predetermined number, and further including divider circuit means coupled to said multiplier circuit means for subsequently dividing the pulses from said multiplier circuit means by a predetermined number, so as to compute the volume of air expired by the subject during each of time intervals corrected to body temperature conditions and to produce electrical output pulses representative of the corrected volume;

sampling means coupled to said metering means for extracting a sample of the expired air therefrom having a proportionate relationship to the total volume of air expired by the subject during each of the given time intervals;

carbon dioxide measuring means coupled to said sampling means for measuring the concentration of carbon dioxide in each sample of the expired air and for producing output electrical pulses having a repetition frequency representative of the concentration of carbon dioxide in each such sample; and

carbon dioxide computer means coupled to said carbon dioxide measuring means and to said volume computer means and including multiplying circuit means for multiplying the output pulses from the carbon dioxide measuring means with the output pulses from the volume computer means to produce electrical output pulses representative of the carbon dioxide production in the expired air of the subject for each given time interval.

2. The apparatus defined in claim 1, and which includes oxygen measuring means coupled to said sampling means for measuring the concentration of oxygen in each sample of the expired air and for producing output electrical pulses having a repetition frequency representative of the concentration of oxygen in each such sample;

and oxygen uptake computer means coupled to the oxygen measuring means and to the volume computer means and including multiplying circuit means for multiplying the output pulses from the oxygen measuring means with the output pulses from the volume computer means for producing electrical output pulses representing the oxygen uptake in the expired air of the subject for each given time interval.

3. The apparatus defined in claim 2, in which the carbon dioxide computer meanS includes circuit means coupled to the oxygen uptake computer means for comparing the output pulses from said carbon dioxide measuring means with the output pulses from the oxygen measuring means to determine the ratio between carbon dioxide production and oxygen depletion in the expired air of the subject for each of the given time intervals.

4. The apparatus defined in claim 3, and which includes separate display means connected to said volume computer means, to said oxygen uptake computer means and to said carbon dioxide computer means;

and circuit means included in said carbon dioxide computer means for generating a timing signal and for applying said timing signal to said volume computer means and to said oxygen uptake computer means for simultaneously controlling the output information from all of the computer means to said display means.

5. The apparatus defined in claim 2, in which said carbon dioxide computer means is coupled to said oxygen uptake computer means for deriving a signal representative of ambient pressure therefrom;

and circuit means included in said carbon dioxide computer means for utilizing said ambient pressure signal to correct the carbon dioxide production calculations in said carbon dioxide computer means to ambient pressure conditions.

6. The apparatus defined in claim 2, in which said oxygen uptake computer means is coupled to said carbon dioxide computer means to permit said carbon dioxide computer means to modify the oxygen uptake in the expired air computation by the oxygen uptake computer means so as to compensate for the carbon dioxide production in the expired air and thereby to provide a true oxygen depletion computation for the expired air.

7. The apparatus defined in claim 1, in which said carbon dioxide measuring means includes a thermal conductivity cell having a first channel through which the expired air sample flows, and a second channel in which dry reference air is circulated, and which includes electrical bridge circuit means including sensing means in said first and second channels for comparing the thermal conductivity of the air in said first and second channels, and output circuit means connected to said bridge circuit means for producing an electrical analog output signal indicative of the thermal conductivity of the sample in said first channel as compared with the reference air in said second channel.

8. The apparatus defined in claim 7, and which includes control circuit means including solenoid valves interposed between the sampling means and the first channel of the thermal conductivity cell for replacing the sample in said first channel with dry reference air, and which further includes automatic zeroing circuit means connected to said bridge circuit means and responsive to a setting signal for balancing said bridge circuit means to reduce the output of said output circuit means to zero when the dry reference air is in the first channel.

9. The apparatus defined in claim 8, in which said zeroing circuit means includes network means for developing, storing and applying a reference balancing value to said bridge circuit means to maintain a zero reference value in said output circuit means for subsequent thermal conductivity measurements until a reset signal is received to recycle said dry reference air.

10. The apparatus defined in claim 1, in which said carbon dioxide measuring means includes an infrared cell having a channel through which the expired air sample flows, and which includes circuit means coupled to the cell for producing an electrical analog output signal indicative of the percent concentration of the sample in the cell.

11. The apparatus defined in claim 10, and which includes control circuit means including selenoid valves interposed between the sampling means and the channel of the infrared cell for replacing the sample in the channel with dry reference air, and which further includes automatic zeroing circuit means for reducing the analog output signal to zero when the dry reference air is in the cell.

12. Carbon dioxide measuring apparatus for measuring the concentration of carbon dioxide in a sample of expired air, said apparatus including;

a thermal conductivity cell having a first channel and a second channel;

first and second electrical sensing means respectively mounted in the first and second channels;

electric bridge circuit means connected to said sensing means for producing an electrical analog output when the thermal conductivity of a gas in the first channel is different from the thermal conductivity of a gas in the second channel;

output circuit means connected to said bridge circuit means;

means for introducing the expired air sample to the first channel of said cell;

means for circulating dry reference air in the second channel of said cell;

a source of dry reference air;

electrically operated solenoid valve means interposed between said introducing means and said first channel of said cell for selectively replacing the expired air sample in the first channel of said cell with dry reference air from said source; and

zeroing control circuit means connected to said solenoid valve means and to said bridge circuit means for controlling said solenoid valve means for the selective replacement of the expired air sample in the first channel with the dry reference air, and for balancing said bridge circuit means for zero output when the dry reference air is in the first channel.

13. The apparatus defined in claim 12, in which said zeroing circuit means includes network means for developing, storing and applying a reference balancing value to said bridge circuit means to maintain a zero reference value in said output circuit means for subsequent thermal conductivity measurements until a reset signal is received to recycle said dry reference air.