Popis: |
On Earth, human body is designed and adapted to operate under uniform gravitational acceleration, 9.8 m/s2 termed as 1 g. However, exposure to microgravity or weightlessness as experienced by astronauts causes significant alterations in the functioning of human cardiovascular system. Due to limitations in using real microgravity platforms, researchers opted for various ground-based microgravity analogs to study effects of microgravity on human cardiovascular system. Although 6º head-down tilt (HDT) is widely used to study the effects on cardiovascular system in space, the net effect of microgravity on the body of an astronaut is the resultant of postures at different inclinations ranging from 0º to 360º as the astronaut’s posture continuously changes due to the absence of gravity. Therefore, in the present study, an investigation of various cardiac parameters and their circulatory adaptation in 18 healthy male subjects was undertaken by using an indigenously developed 360º rotating platform. Cardiac pulse was recorded from 0º to 360º in steps of 30° inclination using piezoelectric pulse sensor MLT1010 and parameters such as average t1, t2, ratios P2/P1, t2/t1, V/P1, systolic blood pressure(SBP), diastolic blood pressure (DBP), heart rate (HR), stroke volume (SV) and cardiac output (CO) were analyzed. The results showed significant changes in the pulse shape and variation in cardiac parameters during the rotation from 0° to 360°. SBP and DBP were found to be decreased during the upright (90°) and upside-down positions (270°). Similar trend was observed for SV and CO except HR. Interestingly, when rotated from 0º to 360º, the cardiac parameters showed an oscillating pattern and the response became normal after returning to supine posture indicating the ability of the cardiovascular system to reversibly adapt to the postural changes. The changes in cardiac parameters at an inclination 270°, in particular, were found to be comparable with spaceflight studies. Based on our findings, we herewith propose that the rotation at head down tilt inclination (270°) along with other inclinations could represent a better microgravity analog for understanding the cumulative cardiac response of astronauts in space. |