Research Express@NCKU Volume 5 Issue 6 - August 29, 2008 [ http://research.ncku.edu.tw/re/articles/e/20080829/1.html ]
Epidemiological Study on the Effect of
Pre-hypertension and Family History of
Hypertension on Cardiac Autonomic Function
Jin-Shang Wu
12*, Feng-Hwa Lu
12, Yi-Ching Yang
12, Thy-Sheng Lin
3,
Jia-Jin Chen
4, Chih-Hsing Wu
2, Ying-Hsiang Huang
2, Chih-Jen
Chang
121Department of Family Medicine, College of Medicine, National Cheng Kung University,
2Department of Family Medicine, National Cheng Kung University Hospital,
3Department of Neurology, College of Medicine, National Cheng Kung University,
4Institute of Biomedical Engineering, National Cheng Kung University, Taiwan, ROC
*Email: [email protected]
J Am Coll Cardiol 2008;51:1896-1901
E
vidence from studies of both animals and humans suggests that the autonomic nervous system plays a crucial role in the development of hypertension, and that autonomic dysfunction underlies the initiation and maintenance of hypertension. Cardiac autonomic function (CAF) can be measured using traditional tests, such as a change in the ratio between the RR intervals during expiration and inspiration (E/I ratio) while deep breathing and the ratio between around the 30th and the 15th RR intervals after standing from the supine position. Heart rate variability (HRV), an indirect measure of cardiac autonomic function (CAF), is a useful tool for evaluating sympathetic and parasympathetic modulation of the heart (Table 1).There has been a hospital-based study of CAF in subjects with high-normal blood pressure of 130-139/85-89 mmHg, rather than 120-139/80-89 mmHg revised by JNC 7 (Seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure). The studies on CAF alteration in normotensive subjects with a family history of hypertension (FHH) defined normotension as a blood pressure < 140/90 mmHg, not the revised values of < 120/80 mmHg. Thus, all the above studies may result in a classification bias. We explored the effects of pre-hypertension and FHH on the CAF from the epidemiological data collected in Taiwan.
Community-dwellers were recruited from an epidemiological study on chronic diseases conducted in Tainan city, Taiwan. A three-stage sampling method was used to generate a stratified systematic cluster sample of households throughout the city. A total of 2416 subjects were eligible from the seven selected areas and 1638 subjects (67.8%) completed the study protocol. Finally, 1436 participants were included in the analysis after excluding 202 subjects who had taken medications known to influence CAF. A positive FHH was confirmed when at least one of the subject’s parents had a documented history of hypertension. According to the JNC 7 criteria, the average of two seated readings of blood pressure can be classified as normotension (blood pressure < 120/80 mmHg without history of hypertension), pre-hypertension (blood pressure of 120-139/80-89 mmHg without history of pre-hypertension), and
hypertension (blood pressure of ≥ 140/90 mmHg or a documented history of hypertension). RR intervals for the beat-to-beat duration of the cardiac cycle were measured continuously with an EKG monitor (CardiSuny α 800, Fukuda M-E Kogyo Inc. Tokyo, Japan) on a personal computer-based data-acquisition system. The analog signals were immediately sent to the signal-acquiring and processing system (DAQPad-6020E and SCB-68, National Instruments, NI) and stored in a personal computer. The EKG signals were processed for R-peak detection using the LabViewTM 6.1 software program (National
hypertension. There were significant differences in age, gender, BMI, the average of two seated systolic/ diastolic blood pressure and heart rate, fasting plasma glucose, cholesterol, triglyceride, and HDL-C, and the prevalence of current alcohol use among these four groups.
Table 2. Comparison of clinical variables among subjects with different blood pressure, including normotension with and without a family history of hypertension, pre-hypertension, and hypertension
NT(-), normotension without a family history of hypertension; NT(+), normotension with a family history of hypertension.; SBP/DBP, average of two seated systolic/diastolic blood pressure readings; HR, average of two seated heart rate readings; * Kruskal-Wallis test.
Figure 1 shows a comparison and adjusted means of CAF among different blood pressure groups from ANCOVA, which was adjusted for age, gender, body mass index, current alcohol use, plasma glucose, cholesterol, triglyceride, and HDL-C. Parasympathetic drive, as indicated by the E/I ratio, the max30/15min ratio, and HF power, decreased in subjects with NT(+), pre-hypertension, and
hypertension. The square root of LF/HF ratio increased in both the pre-hypertension and hypertension individuals, but an increase in LF power existed only in subjects with pre-hypertension.
By mapping the CAF across different blood pressure groups, from NT(-), NT(+), then to
In conclusion, 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. In the future, intervention studies are needed to clarify the role of autonomic function in the preventive strategy of high blood pressure in subjects with FHH and pre-hypertension.
