Capnometer
First Claim
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1. A capnometer comprising:
- a light source for irradiating an infrared radiation to respiratory gas;
a thermal detector for sensing the transmission of said infrared radiation;
means for turning said light source on and off at predetermined intervals;
a memory for storing output from said thermal detector; and
control means for picking up a maximum value of said detection signal from said thermal detector for the present inspiration phase, for storing said maximum value in said memory and calculating the difference between a subsequently issued detection signal and said maximum value, for compensating a drift resulting from the characteristics of said thermal detector to determine a density signal, for picking up a minimum output value, corresponding to an offset value, of said detection signal from said thermal detector when said light source is turned off momentarily, for calculating the difference between said minimum value and said maximum value for the present inspiration phase, for storing the difference in said memory as a reference value corresponding to carbon dioxide concentration of zero and with a maximum reception of infrared radiation at that time, for storing said reference value in said memory, for calculating the ratio of said density signal to said reference value, and for determining the concentration of carbon dioxide by correcting said density signal in accordance with said ratio.
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Abstract
A capnometer is disclosed with a light sourse for irradiating a respirtory gas, a thermal detector for sensing the transmission of the infrared radiation, a switch device for turning the radiation source on and off in a predetermined period, a memory device for storing output from the thermal deterctor, and a control device for picking up a maximum value of the detection signal from the thermal detector for the present inspiration phase. The maximum value is stored in the memory device and the difference is calculated between a subsequently issued detection signal and the stored maximum value to compensate for drift that has occurred in the thermal detector.
9 Citations
12 Claims
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1. A capnometer comprising:
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a light source for irradiating an infrared radiation to respiratory gas; a thermal detector for sensing the transmission of said infrared radiation; means for turning said light source on and off at predetermined intervals; a memory for storing output from said thermal detector; and control means for picking up a maximum value of said detection signal from said thermal detector for the present inspiration phase, for storing said maximum value in said memory and calculating the difference between a subsequently issued detection signal and said maximum value, for compensating a drift resulting from the characteristics of said thermal detector to determine a density signal, for picking up a minimum output value, corresponding to an offset value, of said detection signal from said thermal detector when said light source is turned off momentarily, for calculating the difference between said minimum value and said maximum value for the present inspiration phase, for storing the difference in said memory as a reference value corresponding to carbon dioxide concentration of zero and with a maximum reception of infrared radiation at that time, for storing said reference value in said memory, for calculating the ratio of said density signal to said reference value, and for determining the concentration of carbon dioxide by correcting said density signal in accordance with said ratio. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method for measuring the concentration of carbon dioxide in respiratory gas, comprising the steps of:
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irradiating an infrared radiation from a light source to said respiratory gas; sensing the transmission of said infrared radiation; turning said light source on and off at predetermined intervals; detecting radiation transmitted through said respiratory gas with a thermal detector; storing output from said thermal detector; detecting a maximum value of a detection signal output from said thermal detector for the present inspiration phase; storing said maximum value in a memory; calculating the difference between a subsequently issued detection signal and said maximum value; compensating a drift resulting due to the characteristics of said thermal detector to determine a density signal; detecting a minimum output value, corresponding to an offset value, of said detection signal from said thermal detector when said light source is turned off momentarily; calculating the difference between said minimum value and said maximum value for the present inspiration phase; storing a value representing the difference in said memory as a reference value corresponding to carbon dioxide concentration of zero and with a maximum reception of infrared radiation at that time; storing said reference value in said memory, calculating the ratio of said density signal to said reference value; and determining the concentration of carbon dioxide in said respiratory gas by correcting said density signal in accordance with said ratio. - View Dependent Claims (8, 9, 10, 11, 12)
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Specification
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Current AssigneeNihon Kohden Corporation
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Original AssigneeNihon Kohden Corporation
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InventorsIto, Masami, Inoue, Masayuki, Sugiura, Masaki, Yamamori, Shinji, Ono, Kohei, Hosaka, Hidehiro
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Primary Examiner(s)ALEXANDER, LYLE
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Application NumberUS08/605,845Time in Patent Office750 DaysField of Search422/83-84, 436/133, 436/134US Class Current436/133CPC Class CodesA61B 5/0836 Measuring rate of CO2 produ...Y10T 436/204998 Inorganic carbon compounds
