Implication of base heart rate in autonomic nervous function, blood pressure and health-related QOL

Increased resting heart rate (HR) and increased sympathetic nervous activity are independent risk factors for cardiovascular disease. Recently, base heart rate (HRo: minimum stable HR during sleep) has been reported to relate to cardiac stroke volume and age. However, little is known about the relevance of HRo. The aim of our study was to evaluate how HRo is associated with HR variability (HRV), blood pressure and health-related quality of life (HRQOL) in healthy subjects. A total of 139 volunteers participated in this study that measured 24-hr HR, HRV, and blood pressure. HRo was estimated from the trendgram and the histogram of HR during the nighttime (sleep) period, and calculated as the 1% lowest value of its integral. HRQOL was assessed by Medical Outcome Study Short-Forum 36-Item Health Survey. Sympathetic nervous activity (ratio of low frequency to high frequency component: LF/HF) and parasympathetic nervous activity (high frequency component: HF) were calculated by ECG monitoring. HRo was positively correlated with 24-hr LF/HF and nighttime LF/HF. HRo was negatively correlated with 24-hr HF and nighttime HF. Moreover, HRo was positively correlated with the scores of social functioning and role-physical. Using multivariate analysis, HRo is related to LF/HF, body mass index, and the score of social functioning (HRQOL). HRo may be a useful indicator for assessing sympathetic nervous activity and HRQOL in normotensive healthy subjects.