The relationship between blood volume, blood properties and work capacity.

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The mechanism to increase exercise performance or maximal oxygen uptake has been widely studied from the point view of cardiovascular performance or oxygen carrying capacity, while controversy exists as to whether blood volume expansion has the potential to increase maximal oxygen uptake.In this experiment, maximal oxygen uptake was determined on subjexts with wide range of exercise ability, simultaneously with circulating blood volume and plasma volume. The right atrial pressure and ANP during exercise in air and also with water immersion were determined together with the changes in circulating plasma volume, and the mechanism of plasma volume decrease during exercise was analyzed in the relationship with the ability to exercise.As the results, we found highly significant correlation between blood and plasma volumes and maximal oxygen uptake. In addition, our results indicated that the increase of maximal oxygen uptake is more related with the increase of plasma volume than that of blood volume.During exercise at 60% of maximal oxygen uptake, circulating plasma volume showed decrease by about 4% on an average, and the decrease showed correlation with the increases in plasma ANP.Plasma ANP showed high correlation with the product of right atrial pressure and heart rate than with right atrial pressure alone, which suggests that stimuli for ANP secretion is right atrial pressure during heart contraction. Similar results were obtained from the experiment on rats in which circulating blood volume and blood properties were measured continuously on by-passed extra-corporeal circulation.Summarizing these results, it is suggested that the plasma volume expansion is favorable for the maintenance of cardiac output, and regulation of body temperature during exercise. It is also suggested that the increase in plasma volume and the decrease in heart rate with exercise training contribute to maintain exercise performance.