Determination of cardiac size from chest roentgenograms following Skylab missions

The majority of crewmembers who exhibited postflight decreases in the cardiac silhouette size also showed a decreased orthostatic tolerance to lower body negative pressure. Similar findings were also reported by the Soviet investigators following 30-day bedrest studies and in cosmonauts upon return from space missions. Further radiological data from all three Skylab manned missions are presented and the physiological factors possibly involved in the cardiac silhouette changes are discussed.