The Japanese journal of physiology
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When mixed venous blood is oxygenated in alveolar air with higher PCO2, the PCO2 within the red cell is though to exceed the alveolar PCO2 due to the Haldane effect and to block the inward CO2 diffusion. If the direction of the CO2 diffusion is not reversed during the contact time, the HCO2-gain in the plasma will not exceed the amount estimated from venoalveolar PCO2 difference by using a CO2 dissociation curve of separated plasma. In order to clarify the validity of the above thought, the venoarterial CO2 content difference was measured by using a van Slyke apparatus and a PCO2 electrode at various alveolar PCO2 levels in rebreathing dogs. ⋯ The reduction, however, was slightly stronger in normoxia than in hyperoxia with alveolar PO2 of 300 to 420 mmHg. These data seem to support the following explanation: When venous blood was oxygenated in normoxic air with PCO2 higher than true venous, the inward CO2 diffusion was inhibited by the Haldane effect and the reversed diffusion after the oxygenation could also be disregarded during the contact time. Because the oxygenation was accelerated in hyperoxia and the direction of the CO2 diffusion was reversed earlier than in normoxia, the plasma CO2 content became higher in hyperoxia than in normoxia.
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The transvascular fluid shift after blood volume modification was analyzed by means of continuous blood volume determination and stimulation analysis. On splenectomized dogs, 15% of the circulating blood was withdrawn and retransfused, while the circulating blood volume, hematocrit and colloid osmotic pressure were continuously monitored. Based on the results, the transvascular fluid shift was stimulated by a two-compartment model. ⋯ The compliance of the vascular space, 4.62 +/- 0.82 ml/mmHg . kg of body weight, was almost identical with that of the interstitial fluid space, 4.75 +/- 1.52 ml/mmHg . kg of body weight. The whole body capillary filtration coefficient was 0.74 +/- 0.39 ml/min . mmHg . kg of body weight, which is within the range of the reported values of the capillary filtration coefficient for muscle and intestine. It is suggested that the rapid transvascular fluid shift after blood volume modification is provided with the fact that the compliances of intravascular and interstitial fluid spaces are almost identical.