Impact of acute respiratory stress on cardiac autonomic control in young healthy subjects explored by time and frequency domain methods.

To find the possible utility of analysis of heart rate variability in quantifying transient cardiac autonomic modulation, we assessed the impact of breath holding-induced acute respiratory stress on heart rate variability parameters and blood pressure in young healthy subjects. In ten healthy subjects aged between 22-24 years of either sex, R-R intervals and blood pressure were recorded for one minute under resting state, during breath holding and immediately after withdrawal from breath holding. Heart rate variability was quantified by time and frequency domain methods. Mean differences in values were compared separately between resting and during breath holding, during and following withdrawal from breath holding; resting and following withdrawal from breath holding employing paired 't' test. Blood pressure and standard deviation of R-R intervals (SDNN) significantly increased during breath holding and decreased following withdrawal from it. Low frequency power in normalized units (LF nu) significantly decreased, while the high frequency power in normalized units (HF nu) significantly increased with a resulting decrease of the LF/HF ratio following withdrawal from breath holding compared to during breath holding. During the recovery phase only the LF% power significantly decreased as compared with the resting state. Thus, blood pressure and SDNN appeared to better quantify the ability of the heart to meet changing situational demands. LF nu and HF nu or LF/HF ratio reflected the behavior of sympathetic and parasympathetic limbs in adapting to changing situational demand.