The Medical Aspects of Space Flight Seen from the Viewpoint of Nuclear Medicine

Radionuclide volume measurements performed on crews of selected Apollo missions indicate the following: (1) Invariably, there is a small drop in red-cell mass of the returning crewmembers; (2) plasma-volume decreases similar to those experienced during bedrest are found in crewmen of short Gemini missions. After longer missions, the plasma-volume decrease is no longer present; (3) extracellular- and total-body water changes prove that spaceflight weight loss includes actual tissue losses; and (4) the loss of total-body exchangeable potassium after the Apollo 15 mission is evidence of increased aldosterone secretion.