Autonomic Nervous Functions in Fetal Type Minamata Disease Patients: Assessment of Heart Rate Variability

Autonomic Nervous Functions in Fetal Type Minamata Disease Patients:
Assessment of Heart Rate Variability

TOMOKO OKA,^1,2 MAKOTO MATSUKURA,² MIWAKO OKAMOTO,³ NORIAKI HARADA,⁴
TAKAO KITANO,¹ TERUHISA MIIKE² and MAKOTO FUTATSUKA¹

¹Department of Public Health, and ²Department of Child Development, Kumamoto University School of Medicine, Kumamoto 860-0811, ³Meisuien, Minamata Municipal Welfare Institute for Minamata Disease Patients, Kumamoto 967-0008, ⁴Department of Human Environment and Preventive Medicine, Yamaguchi 755-8505

In order to assess the cardiovascular autonomic nervous functions in patients with fetal type Minamata disease (FMD), we investigated blood pressure (BP), and conducted time and frequency domain analysis of heart rate variability (HRV). Subjects were 9 patients in Meisuien recognized as FMD, and 13 healthy age matched control subjects. HRV and BP were assessed after subjects rested in a supine position for 10 minutes. Electrocardiographic (ECG) data were collected for 3 minutes during natural breathing. Time domain analysis (the average of R-R intervals [Mean RR], standard deviation of R-R intervals [SD RR], coefficient of variation [CV]), and frequency domain analysis by fast Fourier transformation (FFT) (power of low frequency [LF] and high frequency [HF] component, expressed in normalized units[nu]) were then conducted. In the time domain analysis, the mean RR of the FMD group was significantly lower than that of the control group. Neither SD RR nor CV showed significant differences between the two groups, but both tended to be lower in the FMD group. In the frequency domain analysis, the HF component of the FMD group was significantly lower than that of the control group. Pulse pressure (PP) was significantly lower in the FMD subjects. These findings suggest that parasympathetic nervous dysfunction might exist in FMD patients, who were exposed to high doses of methylmercury (MeHg) during the prenatal period. Decrease of PP might be due to degenerative changes of blood vessels driven by exposure to high doses of MeHg.

Keywords —— fetal type Minamata disease; autonomic nervous functions; heart rate variability; methylmercury

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Tohoku J. Exp. Med., 2002, 198, 215-221

Address for reprints: Tomoko Oka, Department of Public Health, Kumamoto University School of Medicine, 2-2-1 Honjo, Kumamoto 862-0976, Japan.

e-mail: 001m9010@med.stud.kumamoto-u.ac.jp