Heart rate variability in exposure to high altitude hypoxia of short duration.

The objective of the presented studies is to attempt an evaluation of heart rate (HR) and heart rate variability (HRV) regulatory mechanisms in the presence of autonomous nervous system (ANS) components in transient exposure to high altitude hypoxia. During 24 hrs including a stay in hypobaria, the participants had their HR continuously recorded using the Holter method. The following parameters were calculated at rest and during the stay in a thermobarochamber: spectral power in low frequency bands (LF) 0.04-0. 15 Hz and high frequency bands (HF) 0.15-0.5 Hz, and the sympathetic-parasympathetic balance index LF/HF. Under hypobaric conditions, a decrease in mean spectral power of R-R intervals was noted within both frequency ranges, compared with the study performed in normobaria. The observed differences were larger at daytime.

Effect of low acceleration simulator training on +Gz acceleration tolerance level.

The goal of this paper was studying the effectiveness of frequently repeated low values of long duration acceleration on circulatory system response during gradual onset rate of acceleration on a human centrifuge.

Heart rate variability during centrifuge (+Gz) and lower body negative pressure (LBNP) in pilot candidates.

NASA: Electrocardiograms were recorded in healthy men undergoing centrifugation and lower body negative pressure. Heart rate variability was studied in conjunction with acceleration tolerance. Specific results allowed the authors to conclude that there was significantly lower sympathetic nervous system activity in individuals with high acceleration tolerance.^ieng