The Influence of Gravity on Cardiorespiratory Regulation: a Comparison of Short-duration Spaceflight and the Esa Short- Arm Human Centrifuge

Respiratory Sinus Arrhythmia (RSA), usually the high frequency (HF) component of heart rate variability (HRV), is a cardiorespiratory interaction mediated by the vagus nerve. RSA is thus considered a marker of the parasympathetic modulation of heart rate. Previous studies reported decrease in RSA after spaceflight. Whether this can be due to autonomic adaption to microgravity or only result from a decreased blood volemia is still a matter of debate. The ESA Short-Arm Human Centrifuge (SAHC) was used to expose 6 male subjects to 3 different G-levels along the head-to-feet axis (Gz). It is hypothesized that hyper-G can generate blood pooling in the legs that can mimic the postspaceflight autonomic response as the one observed through the analysis of RSA during imposed and controlled breathing (ICB) protocols. Results from SAHC experiments are compared to results from similar ICB experiments performed before, during and after a short-duration (the 11 days odISSea) space mission.