Respiratory gas concentration measuring apparatus

• US 4,522,204 A
• Filed: 06/08/1983
• Issued: 06/11/1985
• Est. Priority Date: 06/22/1982
• Status: Expired due to Fees

• Current Assignee: Nihon Kohden Corporation
• Original Assignee: Nihon Kohden Corporation
• Inventors: Yamamori, Shinji, Kurahashi, Muneshige
• Primary Examiner(s): Howell, Kyle L.
• Assistant Examiner(s): SMITH, RUTH S
• Application Number:
  US06/502,133
• Time in Patent Office: 734 Days
• Field of Search: 128/665, 128/666, 128/719, 73/23, 250/214 C, 250/565, 250/343, 356/39-42, 356/418, 356/419
• US Class Current: 600/532
• CPC Class Codes: A61B 5/0836 Measuring rate of CO2 production
• CPC Class Codes: G01N 33/497 of gaseous biological material, e.g. breath

Abstract

A respiratory gas concentration measuring apparatus includes a chopper having a first filter for passing therethrough light from a light source and having a first wavelength which can be absorbed by a gas to be measured and a second filter for passing therethrough light from the light source and having a second wavelength which cannot be absorbed by the gas. The chopper is rotatable to position the first and second filters alternately in a light path. The light having passed through the filters is converted by a photodetector into an electric signal. A first detector detects an output from the first filter based on the electric signal, and a second detector detects an output from the second filter based on the electric signal. The apparatus has a power computing circuit for raising an output from said second detector to an mth power, m being a power exponent preset in the power computing circuit, and a divider circuit for dividing an output from the first detector by an output from the power computing circuit. The power exponent m is the ratio between a temperature-dependent coefficient θ₁ of the output of the first detector which varies exponentially with a temperature variation and a temperature-dependent coefficient θ₂ of the output of the second detector which varies exponentially with a temperature variation.

Claims

1. A system for measuring the concentration of a respiratory gas that absorbs light having a first wavelength, including:

(a) a connector tube having an open first end for receiving the respiratory gas, an opposite open end, and an air-tight window between ends;

(b) a light source located adjacent a first side of the window for directing light through said window;

(c) a chopper located adjacent a second side of the window in the path of the light directed through the window, including

(1) at least one first filter means for passing through the light of a first wavelength from said light source, and

(2) at least one second filter means for passing through the light from said light source of a wavelength that is not absorbed by said respiratory gas;

(d) motor means connected to the chopper to position said first and second filter means alternately in said light path;

(e) a photodetector means located adjacent the chopper for receiving light passing therethrough and converting the light having passed through said filter means into a first electric signal;

(F) a first detector means connected to the photodetector means for receiving the first electric signal therefrom and operated synchronously with said motor means for generating a second electric signal indicative of the amount of light passing through the first filter means;

(g) a second detector means connected to the photodetector means for receiving the first electric signal therefrom and operated synchronously with said motor means generating a third electric signal indicative of the amount of light passing through the second filter means;

the improvement comprising;

(h) a power computing circuit means connected to the second detector means for receiving the third electric signal therefrom and generating a fourth electric signal equal to the third electric signal raised to a preset mth power, m being the ratio between

(1) a temperature-dependent coefficient θ

₁ of the second electric signal which varies exponentially with a temperature variation, and

(2) a temperature-dependent coefficient θ

₂ of the third electric signal which varies exponentially with a temperature variation; and

(i) a divider circuit means connected to the first detector means and the power computing circuit means for receiving the second and fourth electric signals and dividing the second electric signal by the fourth electric signal to produce a temperature independent electric signal indicative of the concentration of the respiratory gas in the connector tube.