Fluid shifts into and out of superficial tissues under microgravity and terrestrial conditions

The microgravity environment can be expected in man to induce a swelling of facial tissues and a shrinking of the tissues in the lower limbs together with a loss in body weight. To quantitate fluid shifts into and out of superficial tissues an ultrasound A-mode method was used in one cosmonaut during a 7-day spaceflight. Measurements were taken from frontal and tibia tissues, where the underlying bone provides a good backwall echo. During the spaceflight the cosmonaut showed a swelling of facial tissues during the first 3 days. At the same time the superficial tissues of the caudal areas shrank by 20%. In space he lost 7.7% of body weight. After the spaceflight the superficial tissues were dried out but regained their water content within the next 4 days even before body weight returned to control level. Per kilogram of body weight an increase of 400 cm3 entered the superficial tissue layers of the body. It is concluded that water loss as well as wasting of tissues contribute to the loss in body weight during space flight.