Cardiovascular dynamics among differently trained individuals during simulated microgravity exposure in the form of head-down tilt

Abstract

Introduction: Human morphology and physiology are not designed inherently to function in microgravity. Hence, exposure to hypo or microgravity, as it occurs during space exploration, poses challenges in the form of peculiar adaptive physiological processes in healthy astronauts. These changes may vary (to a certain extent) depending on type of physical fitness (namely, aerobic or anaerobic) and may have definitive impact on short duration space mission. The study aimed to examine the cardiovascular dynamics during short duration exposure to simulated microgravity condition in differently trained individuals. Material and Methods: Temporal variations in body fluid distribution were studied during 6° head-down tilt (HDT) for 4-hours in 31 healthy males in age range of 20–40 years divided into three groups based on their physical training, namely; resistance trained (RT), endurance trained (ET), and untrained (UT). This was based on their history of physical training, VO2 max, and peak anaerobic power. Results: Heart rate in the ET group and RT group showed increasing and decreasing trend respectively, however, statistically remained non-significant. Systolic and diastolic pressures showed a significant increase in the ET group at the 4th h of HDT as compared to baseline and the 1st h. No significant variation in pulse pressure could be seen. Mean arterial pressures showed significant increase in the ET group at the 4th h of HDT as compared to baseline and the 1st h of HDT. Stroke volume and cardiac output did not vary significantly. Conclusion: ET individuals in the present study demonstrated decreased sensitivity of baroreceptors than RT or UT individuals, whereas, the RT group demonstrated more stability/resilience in terms of cardiovascular dynamics than ET and UT groups under exposure to short duration simulated microgravity.