Epidemiological Study on the Effect of Pre-Hypertension and Family History of Hypertension on Cardiac Autonomic Function

Objectives: This study sought to examine the hypothesis that cardiac autonomic function (CAF) is altered in pre-hypertensive subjects and normotensive subjects with a family history of hypertension (FHH). Background: The findings on the FHH effect in CAF have been inconsistent, and little is known about altered CAF in pre-hypertensive subjects under The Seventh Report of the Joint National Commission on High Blood Pressure criteria of normotension and pre-hypertension. Methods: A total of 1,436 community dwellers were classified as having normotension without FHH (NT[-]), normotension with FHH (NT[+]), pre-hypertension, and hypertension. Cardiac autonomic function was determined by standard deviation of RR intervals (SDNN), power spectrum in low frequencies (LF) and high frequencies (HF) and LF/HF ratio in supine position for 5 min, the ratio between the longest RR interval at approximately the 30th beat and the shortest RR interval at approximately the 15th beat after standing (30 max/15 min ratio), and the ratio between the longest RR interval during expiration and the shortest RR interval during inspiration (E/I ratio). Results: There was a significant difference in all CAF indexes among subjects with NT(-), NT(+), pre-hypertension, and hypertension. Multivariate analyses with an analysis of covariance model showed that 30 max/15 min ratio, E/I ratio, and HF power decreased in subjects with NT(+), pre-hypertension, and hypertension when compared with NT(-) subjects. Pre-hypertensive and hypertensive subjects displayed higher square roots of LF/HF ratios. Only pre-hypertensive subjects had higher LF power. Conclusions: Our study provides evidence that CAF plays a role in pre-hypertension and that altered autonomic function is already present in subjects with FHH. An autonomic imbalance shifting with augmented sympathetic tone was more enhanced in pre-hypertension.