[Activation of respiratory sinus arrhythmia in monkeys during space flight]

During the first day in space the rhesus monkey, called Vernyi, flown on Cosmos-1667 showed higher values of the daytime, night, and daily respiratory sinus arrhythmia (RSA) when compared to those observed before launch and before or the first day of a simulation study. During orbital flight, the mean daily value of RSA was in the range 13.08-16.00 beats/min. In the simulation study, this parameter increased from 4.68 beats/min during the first day to 15.16 beats/min on the 6th day. The mean RSA values during days 1 through 3 were significantly higher in real than in simulation flight. Analysis of rheopneumograms revealed a correlation between respiration parameters and RSA variations. In space, there was no correlation between RSA and HR, which was reported in the simulation study (r = -0.625). Assuming that RSA is a noninvasive indicator of parasympathetic control over cardiac rhythm, it can be postulated that the primate body adapted to microgravity via activation of parasympathetic mechanisms controlling the heart function.