Studies on weightlessness in a primate in the Biosatellite 3 experiment

In June 1969 a male Macaca nemestrina (pigtail macaque) was flown in earth orbit for 8.8 days in NASA Biosatellite 3. The experiment examined in detail central nervous and cardiovascular functions, and included pre- and post-flight whole body metabolic assessment, in-flight urine analysis, and pre-and post-flight bone density measurements. Although the sleep/wake cycle was 24 hr, a phase angle lag of 2 hr from the imposed night/day mode occurred. A definite desynchronosis occurred, with rhythms longer than 24 hr in pCO2, brain and body temperature and heart rate, although arterial blood pressure remained at 24 hr. Sleep states were remarkably fragmented and unusually brief in duration. Vestibular and ocular disturbances were evident. These changes began concurrently with onset of weightlessness and were not secondary to altered fluid balance or body temperature. Sleep patterns lie between those of normal man and man with high cervical cord transection. There was an immediate and sustained increase in central venous pressure in weightlessness and this is considered to have initiated a Henry-Gauer reflex which initially maintained a high urine volume. This, coupled with a high evaporative fluid loss, produced an early dehydration probably associated with electrolyte imbalances. Body weight was 20% lower at recovery than at launch. Ventricular fibrillation supervened 8 hr after recovery.