Variations in cardiac associated sympathovagal oscillations under short-term heat exposure

Heat stress results in significant cardiovascular adjustments for temperature regulation through heat dissipation. The body employs autonomic and behavioural responses mediated by autonomic nervous system (ANS) to prevent hyperthermia. Therefore, the present study aimed to examine the ANS oscillations to significant heat stress stimuli. Digital lead-II electrocardiogram (ECG) and pulse plethysmogram (PPG) were recorded from control and heat-stressed groups under anesthetised conditions. Tachograms were generated from both ECG and PPG signals. The fast Fourier transform (FFT) was used to analyse the bands using Kubios 3.5.0 software. An unpaired t-test and Bland-Altman test were employed to compare the differences between the two groups. The results demonstrated a significant shift of oscillations toward sympathetic dominance with the withdrawal of parasympathetic activity under heat exposure. The LF oscillations increased and exhibited strong associations between HRV and PRV parameters under the heat stress group. PRV and HRV assess the ANS oscillations and aided with valuable insights into cardiac autonomic function.