The Annals of physiological anthropology
Print ISSN : 0287-8429
Computerized System for Determination of Cardiac Output
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1984 Volume 3 Issue 1 Pages 63-68


The CO2 rebreathing method for the determination of cardiac output has been computerized.CO2 concentration of expired air is analyzed by a infrared CO2 analyzer.The output voltageof the CO2 analyzer is sampled by a micro computer through a 12-bit analog-to-digitalconverter.The values of end-tidal CO2 percentages (FETCO2) during nomal respiration and thepeak values of CO2 percentages in the lung-bag system (FbCO2) during rebreathing are detectedby the computer automatically.The detemination of the partial pressure of CO2 in mixed venous blood (PvCO2) is perfomedby computer analysis.The rise in the partial pressure of CO2 in the lung-bag system (PbCO2)with time (T) is expressed by the equation [chemical formula] This equation can be transfomed logerithmically to [chemical formula] At first, Pvco2 is assumed to be a slightly large value than the last value of PbCO2 and theregression equation of ln (1-PbCO2/PvCO2) on T is calculated by means of the least-squaresanalysis.Then PvCO2 is successively changed positively, and the regression equations arecalculated on each time.The value of PvCO2 which maximize the value of coefficient ofdetermination (r2) is adopted as the very value of PvCO2.The partial pressure of CO2 in arterialblood (PaCO2) is a ssumed to be the same as in end-tidal air.A comparison was made between the cardiac output determined by this computerized andthe conventional CO2 rebreathing methods as described by Jernerus et al.(1963).The valuesobtained by the two methods were almost identical, all of 9 paired deteminations of cardiacoutput obtained during exercise were within 10% of one another and 33 of 36 values during restand recovery were within 20% of one another.The correlation coefficient between the valuesobtained by the two methods was 0.992.The computerized method is a more precise and moreconvenient technique for deteming cardiac output.

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