The relationship between short-term HRV indices and heart rate response to Deep BreathingTest in normal subjects

Normally, at rest, respiration is associated with a sinus arrhythmia due to modulation of the cardiac parasympathetic supply. Deep Breathing Test (DBT) thus assesses the parasympathetic arm of nervous system control of the cardiovascular function. Parameters computed from the heart rate responses to the DBT, namely I-EHR and the EI ratio quantifies the extent of sinus arrhythmia and parasympathetic activity. The short-term Heart Rate Variability (HRV) indices that reflect cardiac parasympathetic activity are pNN50, RMSSD, and HF power. The indices that mirror the combined modulation of sympathetic and parasympathetic cardiac supply are SDNN and Total power (sum of LF and HF powers). We postulated that as the DBT was done at a low frequency of breathing (0.1 Hz), changes in the cardiac sympathetic activity would also contribute to the heart rate responses of DBT. The current study thus explored whether there was any correlation between the DBT values of I-EHR and EI ratio and the HRV indices reflecting combined activity of the cardiac sympathetic and parasympathetic innervation, namely SDNN and Total power. We also determined whether there was any correlation between the same DBT values and HRV indices reflecting purely cardiac parasympathetic fluctuations, namely RMSSD, pNN50 and HF power. Towards this, we did the DBT in 22 healthy male volunteers (aged 25-35 years) and their resting supine ECG and respiration was recorded over 5 minutes for short-term HRV analysis to obtain the HRV indices. Spearmans correlation test was applied between the DBT results (I-EHR and EI ratio) and the HRV indices. The results of our study showed no correlation between the DBT parameters and the HRV indices. In conclusion, our study shows that among the subjects studied, the DBT value of a person did not predict the persons HRV indices. Thus, we found no relationship between the inherent spontaneous cardiac autonomic activity and the Deep Breathing Test values in our subjects.