抄録
The circulating blood volume of healthy adult male volunteers was meas-ured at 12: 00, 18: 00, 24: 00 and 06: 00 under controlled conditions (200 ml fluid intake every three hours, constant supine position, constant room temperature and illumination).
Under these conditions, the circulating blood volume was significantly lower (about 6%, P<0.001) at 24: 00 than at 12: 00 or 18: 00. On the other hand, the hematocrit, measured at the same time, was constant throughout the day. Plasma protein and serum Na and K were slightly, but significantly less at 24: 00 than at 18: 00. An increase of about 5% in the erythrocyte volume in blood depots during the night was observed from the simultaneous determination of the erythrocyte volume and plasma volume. Causal factors of circadian variation of circulating blood volume in this controlled experiment were discussed but the complete explanation of the results remains for further experiments.
The circadian variation in the circulating blood was also measured on subjects during normal active daily life. In these, the circulating blood volume was almost identical at 12: 00 and 24: 00, while the hematocrit decreased by 3.6%(P<0.001).
From these result, it is concluded that erythrocyte is deposited in depots during the night, with concomitant dilution of the blood, so that the circu-lating blood volume remains almost constant with sub jects of normal routine activities.
