Contribution of abdomen and legs to central blood volume expansion in humans during immersion.

The hypothesis was tested that the abdominal area constitutes an important reservoir for central blood volume expansion (CBVE) during water immersion in humans. Six men underwent 1) water immersion for 30 min (WI), 2) water immersion for 30 min with thigh cuff inflation (250 mmHg) during initial 15 min to exclude legs from contributing to CBVE (WI+Occl), and 3) a seated nonimmersed control with 15 min of thigh cuff inflation (Occl). Plasma protein concentration and hematocrit decreased from 68 +/- 1 to 64 +/- 1 g/l and from 46.7 +/- 0.3 to 45.5 +/- 0.4% (P < 0.05), respectively, during WI but were unchanged during WI+Occl. Left atrial diameter increased from 27 +/- 2 to 36 +/- 1 mm (P < 0.05) during WI and increased similarly during WI+Occl from 27 +/- 2 to 35 +/- 1 mm (P < 0.05). Central venous pressure increased from -3.7 +/- 1.0 to 10.4 +/- 0.8 mmHg during WI (P < 0.05) but only increased to 7.0 +/- 0.8 mmHg during WI+Occl (P < 0.05). In conclusion, the dilution of blood induced by WI to the neck is caused by fluid from the legs, whereas the CBVE is caused mainly by blood from the abdomen.