Heart rate variability in healthy volunteers during normobaric and hyperbaric hyperoxia

inhaled supranormal partial pressure of oxygen induces bradycardia and peri pheral vasoconstriction. The exact mechanism of the decreasing heart rate i s not clear, but the autonomic nervous system is partly involved. In the pr esent study the role of the autonomic nervous system in hyperoxic bradycard ia was evaluated by using the power spectral analysis of heart rate variabi lity. Ten healthy volunteers participated in four experiments: (i) hyperbar ic oxygen treatment (100% oxygen at 2.5 ATA), (ii) hyperbaric air treatment (O-2 21% at 2.5 ATA), (iii) oxygen treatment at normal pressure (100% O-2, 1 ATA) and (iv) air breathing at normal pressure (21 % O-2, 1 ATA). During the experiments, ECG was registered and subjected to power spectral analys is. The volunteers rated their perception of temperature, ear discomfort, s weating and excitement on a Visual analogue scale. Statistical comparison o f the results of the four trials was conducted with a two-way ANOVA for rep ealed measurements. Heart rate decreased during all interventions, but ther e were no statistically significant differences between the sessions. High frequency variability of heart rate variability and Hayano's index of HF po wer increased and LF/HF ratio decreased with increasing partial pressure of oxygen. Our results suggest, that normobaric and hyperbaric hyperoxia incr ease parasympathetic influence in the regulation of the heart.