Immediate changes in cardiac autonomic tone and stroke volume during microgravity simulation using head-down tilt

Objectives: Gravity plays an important role in the day-to-day functioning of cardiovascular system (CVS) human body. The absence gravity severely affects CVS functioning. Out existing simulation models microgravity, 6° head-down tilt (HDT) is frequently used analog to replicate physiological effects microgravity on earth. Materials and Methods: present study has been designed determine specificity HDT usage as a simulation. heart rate variability (HRV), blood pressure (BP), cardiac output (CO), stroke volume (SV) responses 5 min exposures were investigated for 4°, 6°, 8° HDT. It was hypothesized that graded around will demonstrate reversal autonomic parameters. conducted 28 male subjects aged 20–30 years. Results: reveals there significant rise diastolic mean BP at compared baseline. also observed high-frequency power HRV increased ( P = 0.026), with concomitant reduction low-frequency 0.03) HRV. CO baseline 0.037 0.021, respectively). There no changes any recorded parameters 4° cardiopulmonary receptors might have sensed change passively shifts cephalad. To overcome low problem, tried pump extra through CO. At HDT, it sympathetic activity increased, which not during exposures. Conclusion: suggests head-down-tilt best level producing earth immediate balanced compromise vagal without activation activity. Therefore, our data provide evidence support responses.