One of the physiological answers in diving is bradycardia, however the mechanisms that cause this diminution of the heart rate are unknown.

Aim: 

In the present study we were to know the effects of the hyperbaric pressure on the modulation of the heart rate, where the possible alterations of heart rate variability were observed.

Methods: 

Ten subjects (dive-masters and instructors - 38.89 6.33 years old, 72.71 8.64 kg of total weight, and 1.72 0.05 mts of height (mean SD), were put under 1, 2, 3, and 4 Atmospheres Absolute. The protocol was made in a hyperbaric chamber, with the knocked down subject and measured by ten minutes/atmosphere. Heart rate variability analysis was made in the frequency domain (Fast Fourier Transform and Wavelet).

Results: 

we confirmed bradYcardia with the increase of the atmospheres. The significant diminutions appear from 3 and 4 atmospheres absolute. The energy of the signal (total power in standardized values) increases becoming progressively significant to 4 atmospheres absolute. High frequency and low frequency ranges of heart rate variability showed the same response in both cases. The peaks of frequency bands did not present conclusive results. Nevertheless, with the Wavelet it was verified that the frequency spectrum tends to move towards the zone of high frequency, an index of cardiac parasympathetic modulation, with the increase of the pressures.

Conclusion: 

These results suggest that increased parasympathetic activity is an important factor in the reduction of heart rate in the present hyperbaric environment.