A comparative study of heart rate variability (HRV) among adult hypertensive and normotensive subjects in the supine position.

Objectives: To compare heart rate variability (HRV) among adult Hypertensive and Normotensive subjects in supine position.

Methods: It was an analytical cross sectional study conducted on two study groups. The cases (n=60) comprised of outpatients (males and females in the age group 20-50 yrs) attending the Medicine OPD of Medical Collage, Kolkata, who were newly diagnosed as cases of hypertension according to JNC seven criteria while the control group (n=50) comprised of age and sex-matched adult normotensive subjects, who were non-smokers, non-alcoholics and were not suffering from any major cardiac, neurological or chronic illnesses. HRV profiling through short-term (5 min) ECG recording of each subject was carried out in the supine position with the help of a digital ECG recording machine (RMS-Polyrite D), with a sampling rate of 256 Hz. From the data so collected, various HRV parameters - both time domain (SDNN, RMSSD, NN50 and pNN50) and frequency domain (VLF, LF and HF) were calculated. Analysis of these parameters revealed the pattern of autonomic influence (sympathetic or parasympathetic predominance) prevalent among the subjects of the study and control groups.

Results: An overall reduction of the time domain parameters SDNN and RMSSD (considered more as markers of sympathetic activity) and frequency domain parameters (total power, LF and HF, all expressed in ms), which are markers of parasympathetic activity, was noted among the hypertensive subjects. However, the reduction in frequency domain parameters was much more (highly significantly) than that of time domain parameters. Also, both age and hypertension had significant independent effects on HRV but their 3-way interaction was found to be statistically insignificant.

Conclusions: The findings of the study thus points towards an autonomic dysregulation (characterized by decreased vagal activity and increased sympathetic activity), as an underlying basis (i.e. an important factor, among others) for hypertension.