Autonomic nervous system non-stationary response to controlled changes in barometric pressure

Autonomic Nervous System (ANS) controls a number of bodily functions, such as the heart rate (HR). However, the ANS response is strongly dependent on the surrounding environment. In particular, changes in barometric pressure have important effects on ANS response, but they are difficult to assess in extreme conditions such as a hyperbaric environment. The main goal of this study was to evaluate the dependence of indices related to the ANS response derived from the electrocardiographic signal (ECG) with barometric pressure. In order to do that, a database consisting of ECG recordings of 30 subjects who were introduced into a hyperbaric chamber was used. The analysed indices were derived from the heart rate variability signal: the power of the low-frequency band (P
LF
: 0.04–0.15 Hz), the power of the high-frequency band (P
HF
: 0.15–0.4 Hz), the ratio of instantaneous P
LF
with respect to the sum of instantaneous P
LF
and instantaneous P
HF
, and the ratio of instantaneous P
LF
with respect to instantaneous P
HF
. High inter-subject variability was observed in the results, but significant differences were found in both P
LF
and P
HF
when pressure gradually increased to 5 atm (initial phase) and then decreased (final phase) with respect to the baseline. Changes in the power ratios were not so significant in general.