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KMID : 0351619630040010033
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Kyungpook Medical Journal
1963 Volume.4 No. 1 p.33 ~ p.46
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DETERMINATION OF MIXED VENOUS AND ARTERIAL PCO₂ FROM FRACTIONAL ANALYSIS OF SINGLE BREATH AND ITS APPLICATION TO THE MEASUREMENT OF CARDIAC OUTPUT IN MAN.
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Abstract
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This method is based upon the O_(2) and CO_(2) analysis of several gas samples collected successively during a single expiration of 7-10 seconds. During this period the CO_(2) rises and the exchange ratio (R) falls rapidly.
Theory; (1) A decrease in blood CO_(2) content, with no change in O_(2) content (R=∞) lowers the PCO_(2). An increase in O_(2) content, with no change in CO_(2) content (R=O) increases the PCO_(2). When R is equal to 0.32, PCO_(2) remains constant.
(2) During expiration the alveolar PCO_(2) increases, reducing the CO_(2) output while the O_(2) uptakes remains unaffected. Thus R is directly related to CO_(2) exchange, which in turn is governed by the venous-alveolar CO_(2) tension difference. As long as the mixed venous PCO_(2) remains unaltered, there must be a linear relationship between alveolar PCO_(2) and R, provided the arterial O_(2) content remains essentially constant.
Application; In each of the gas samples, PCO_(2) and PO_(2), a straight line is obtained as predicted. The true mixed venous PCO_(2) can be read at an R value of 0.32, the arterial-alveolar PCO_(2) at the appropriate R, and the "oxygenated venous blood" PCO_(2) at an R of O. Cardiac output determined by this method at rest amd moderate exercise agree with those obtained by blood analysis methods.
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KEYWORD
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