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CLINICAL STUDY

Effect of essential hypertension on cardiac autonomic function in type 2 diabetic patients

Naohiko Takahashi, MD^*, Mikiko Nakagawa, MD, Tetsunori Saikawa, MD, Tatsuhiko Ooie, MD^*, Kunio Yufu, MD^*, Sakuji Shigematsu, MD^*, Masahide Hara, MD^*, Hiroshi Sakino, MD^*, Isao Katsuragi, MD^*, Toshimitsu Okeda, MD^*, Hironobu Yoshimatsu, MD^* and Toshiie Sakata, MD^*

^* Department of Internal Medicine I, School of Medicine, Oita Medical University, Oita, Japan
Department of Laboratory Medicine, School of Medicine, Oita Medical University, Oita, Japan

Manuscript received December 1, 2001; revised manuscript received March 21, 2001, accepted April 5, 2001.

Reprint requests and correspondence: Dr. Naohiko Takahashi, Department of Internal Medicine I, School of Medicine, Oita Medical University, 1-1 Idaigaoka, Hasama, Oita 879-5593, Japan
takanao{at}oita-med.ac.jp

OBJECTIVES

The aim of this study was to examine the effects of essential hypertension on cardiac autonomic function in type 2 diabetic patients.

BACKGROUND

Hypertension is common in type 2 diabetic patients and is associated with a high mortality. However, the combined effects of type 2 diabetes and essential hypertension on cardiac autonomic function have not been fully elucidated.

METHODS

Thirty-three patients with type 2 diabetes were assigned to a hypertensive diabetic group (n = 15; age: 56 ± 8 years, mean ± SD) or an age-matched normotensive diabetic group (n = 18, 56 ± 6 years). Cardiac autonomic function was assessed by baroreflex sensitivity (BRS), heart rate variability (HRV), plasma norepinephrine concentration and cardiac ¹²³I-metaiodobenzylguanidine (MIBG) scintigraphic findings.

RESULTS

Baroreflex sensitivity was lower in the hypertensive diabetic group than it was in the normotensive diabetic group (p < 0.05). The early and delayed myocardial uptake of ¹²³I-MIBG was lower (p < 0.01 and p < 0.05, respectively), and the percent washout rate of ¹²³I-MIBG was higher (p < 0.05) in the hypertensive diabetic group. However, the high frequency (HF) power and the ratio of low frequency (LF) power to HF power (LF/HF) of HRV and plasma norepinephrine concentration were not significantly different. The homeostasis model assessment index was higher in the hypertensive diabetic group than it was in the normotensive diabetic group (p < 0.01).

CONCLUSIONS

Our results indicate that essential hypertension acts synergistically with type 2 diabetes to depress cardiac reflex vagal and sympathetic function, and the results also suggest that insulin resistance may play a pathogenic role in these processes.

Abbreviations and Acronyms   BRS = baroreflex sensitivity   ECG = electrocardiogram   H/M = heart-to-mediastinum   HF = high frequency component (0.15 to 0.45 Hz)   HOMA = homeostasis model assessment   HRV = heart rate variability   LF = low frequency component (0.04 to 0.15 Hz)   LV = left ventricular   MIBG = metaiodobenzylguanidine   NE = norepinephrine   WR = washout rate

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