Appraisal of Relationship between Hypertension and Short-Term Heart Rate Variability Indices

Background: Hypertension, the silent killer is as an important risk factor for cardiac arrest, stroke, kidney disease and increased mortality rates in adults. Heart Rate Variability (HRV) is a physiological phenomenon of variation in the time interval between heartbeats and is a gold-standard to assess the perpetually changing oscillations of a salubrious heart. Early detection of hypertension by a non-invasive tool as HRV can identify the autonomic regulation in hypertensive individuals at high risk for developing cardiovascular morbidities complications. Aim: To study the autonomic correlates of cardiovascular health in hypertension in terms of short term HRV and to analyze the association between HRV indices and elevated blood pressure. Methods: It was a cross-sectional observational study carried out in Sports Physiology Laboratory in Department of Physiology of a rural medical college in central India. 25 known cases of hypertension (having Systolic BP >140 mmHg and diastolic BP >90 mmHg) in the age group of 35-60 yrs and 75 age matched normotensives as controls (Systolic BP < 120 mm of Hg and Diastolic BP < 80 mm Hg) were selected. ECG was recorded using Power lab data recording system, AD instruments and analysis was done by HRV Module of Lab chart software. The subjects performed an incremental ramp exercise test to the limit of tolerance on a motorized treadmill. Results: The mean age of control males was 39.80±6.68 and mean age of control females was 37.05±2.75. Out of hypertensives, 17 were males (mean age 42.58 ± 6.94) and 8 were females (mean age 42.6±8.84). There was statistically significant difference observed in SDNN, RMSSD, HF%, HF nu between control and cases males but no significant relationship was observed among other parameters in males. On comparing the sympatho-vagal ratio (LF/HF), female cases were having high ratio than control females indicating a dominant sympathetic response. From Pearson’s correlation analysis, a positive non-significant relationship was observed between systolic BP and Frequency domain indices in controls while in cases a negative correlation was found which was also statistically non-significant. A strong positive correlation was found between Systolic BP and SDNN (r=0.55) in hypertensives. The time domain parameters were also found to be negatively correlated with mean heart rate in both controls and cases. Conclusions: This pioneering study analyzed the association between heart rate variability indices and high blood pressure. The analysis of HRV can distinguish parasympathetic from sympathetic influences on the heart and provides important insights into the role of the autonomic nervous system in the pathogenesis of essential hypertension. HRV is reduced in men and women with systemic hypertension. Among normotensive men, lower HRV was associated with greater risk for developing hypertension. These findings clearly exhibit that autonomic dysregulation is present in the early stage of hypertension.