A new indirect method for measuring arteriovenous O2 content difference and cardiac output from O2 and CO2 concentrations by rebreathing air.

Abstract

A new indirect method for measuring the arteriovenous 02 content difference (avDo 2) was developed. The avDo 2 was calculated by dividing the gradient of the C02 dissociation curve by that of a gas exchange ratio against Pco2. The latter slope was obtained from 02 and C02 concentrations in rebreathing air. The validity of the method was tested preliminarily in human subjects by comparing the cardiac output calculated from avDo 2 and 02 uptake (o2) with that measured hitherto by other authors, and then in dogs by comparing the calculated avDo, with the measured value. In the dog experiments, the rebreathing was performed 7 times in each of 7 dogs. Immediately after the rebreathing arterial and mixed venous blood were sampled and analyzed for avDo2. For each rebreathing period the avDo, was calculated by using the C02 dissociation curve obtained in the individual dogs. The correlation coefficient between the measured and calculated avDo2 was 0.87, demonstrating reasonable validity of the method. The Vo2 was further measured from the time interval during which a known amount of pure 02 was consumed. Then, the cardiac output was calculated by dividing the Vo2 by the measured and calculated avDo2. The correlation coefficient between the respective cardiac output values was 0.88, indicating the reliability of using the calculated avDo 2.

A method for estimating contact time of red blood cells through lung capillary from O2 and CO2 concentrations in rebreathing air in man.

“…KAGAWA and MOCHIZUKI (1987) designated the (a-v)Co2 at the PAco2, where the pH~ in arterial blood equals that in venous blood, as the standard (a-v)Co2 ((a-v)Co2*). Furthermore, they developed a method to obtain the (a-v)Co2* by a modification of the method originated by MOCHIZUKI et al (1984). Let the middle between trPvco2 and oxPvco2 be Pm2 and the slope of the C02 dissociation curve at Pmt be a'(Pm2) (vol%.Torr-1).…”

“…Moreover, let the slope of the R-P02 line obtained from gas analysis of rebreathing air be 6. MOCHIZUKI et al (1984) estimated the (a-v) Cot by dividing the a'(Pm2) by 8. Since the (a-v)Co2 thus obtained, however, was not accurate enough, KAGAWA and MOCHIZUKI (1987) derived a correcting factor (F(H)) from the numerical solution of 02 and C02 diffusions in the RBC and attempted to estimate the (a-v)Co2*:…”

“…Taking the above differences into account, the difference in DL(C02) between 180 and 155 ml • min -1 • Torr -1 seems to be permissible. During the outward CO2 diffusion, the inward HCO3 -shift always occurs, raising the intracellular P~o2 SHIMOUCHI et al, 1984;KAGAWA and MoCHIzuKI,1984;MOCHIZUKI et al, 1985). According to the experimental data on the CO2 diffusion in RBC suspension (PIIPER, 1964;CONSTANTINE et al, 1965;NnzEKI et al, 1983), the permeability of CO2 across the RBC membrane is not so great as to be disregarded.…”

Theoretical analyses for arterial-venous O2 content difference and Haldane effect during rebreathing.

“…KAGAWA and M. MOCHIZUKI MocHIZUKI et al (1984) derived an equation to determine the arterial-venous 02 content difference ((a-v)Co2) from the a' and the slope of a gas exchange ratio versus the Pco2 in rebreathing air (9), as given by (a-v)C02 = a'/0. When the C02 equilibrium is not reached, the (v-a)Cco2(H) becomes less than the product of a' • (oxPvco2 -trPvco2).…”

Cardiodynamic factors affecting hyperpnea during steady-state exercise in man.

“…It has been reported that a comparison between the Q values determined by this method and the direct Fick method results in a correlation coefficient of 0.88 in dogs (MOCHIZUKI et a!.,1984). Mixed venous tension of C02 (Pvco2) was determined from the above R-Pco2 replationship by taking the point when R = 0, and converting it into terms of the concentration in the blood (CV02) ~by reading off the C02 dissociation curve.…”