Head out of water immersion as simulation study: an heart rate variability study

During head out of water immersion (HOI), the hydrostatic pressure on the tissues of the lower limbs causes an increase in thoracic blood volume and a high vascular perfusion. This blood shift results in changes in autonomic balance. The aim of this study was to evaluate the activity of the autonomic nervous system, as obtained from the analysis of heart rate variability (HRV), during HOI at 2 different temperatures and compare these results with data obtained during parabolic flight. In HOI, two different positions (sitting and standing) were compared. Results showed a shift to vagal activity as well during HOI as in microgravity during parabolic flight.