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CLINICAL RESEARCH: HYPERTENSION

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

Jin-Shang Wu, MD, MS^_*,, Feng-Hwa Lu, MD, MS^_*,, Yi-Ching Yang, MD, MPH^_*,, Thy-Sheng Lin, MD, MS, Jia-Jin Chen, PhD, Chih-Hsing Wu, MD, Ying-Hsiang Huang, MD, MS and Chih-Jen Chang, MD^_*,,_*

^_* Department of Family Medicine, National Cheng Kung University, Taiwan, Republic of China
Department of Neurology, College of Medicine, National Cheng Kung University, Taiwan, Republic of China
Institute of Biomedical Engineering, National Cheng Kung University, Taiwan, Republic of China
Department of Family Medicine, National Cheng Kung University Hospital, Taiwan, Republic of China.

Manuscript received August 27, 2007; revised manuscript received November 19, 2007, accepted December 2, 2007.

^_* Reprint requests and correspondence: Dr. Chih-Jen Chang, Department of Family Medicine, National Cheng Kung University Hospital, 138, Sheng Li Road, Tainan, 70441, Taiwan, Republic of China. (Email: jins{at}mail.ncku.edu.tw).

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.

Abbreviations and Acronyms   30 max/15 min ratio = a ratio between the longest RR interval at approximately the 30th beat and the shortest RR interval at approximately the 15th beat after standing   CAF = cardiac autonomic function   E/I ratio = a ratio between the RR intervals during expiration and inspiration   FHH = family history of hypertension   HDL-C = high-density lipoprotein cholesterol   HF = high frequency   HRV = heart rate variability   LF = low frequency   NT(–) = normotension without family history of hypertension   NT(+) = normotension with family history of hypertension   SDNN = standard deviation of normal-to-normal intervals or RR intervals

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