[Changes in cardiac output and orthostatic tolerance of astronauts]

Examinations of 14 cosmonauts who performed orbital flights of 14 to 175 days were used to correlate cardiac output (CO) inflight with orthostatic tolerance and LBNP reactions postflight. In 3 crewmembers CO was lower than or close to the preflight level. In 4 cosmonauts CO was higher thant preflight. The remaining 7 crewmembers showed lower orthostatic tolerance and stronger LBNP reactions. The difference between mean CO values before and during flight was in negative correlation with orthostatic tolerance (r = -0.6) and in positive correlation with LBNP reactions (r = 0.7). The correlation coefficients were derived from small samples but an identical relationship between the two different tests with inflight CO variations gives evidence that such a relationship actually exists.