最低心拍数による自律神経トーヌスの推定

Estimation of autonomic nervous tone by evaluating minimal hourly heart rate

　心拍数の日内変動は，身体活動状態に影響を受け，個人差および日差変動が大きい。しかし，安静時の心拍数は各個人特有の自律神経トーヌスを反映し，一定の日内変動を示すことが考えられる。本研究は，安静時自律神経トーヌスの日内変動をホルター心電図による時刻別最低心拍数変動により推定し，運動および加齢の自律神経トーヌスに及ぼす影響を検討したものである。

Autonomic nervous tone was estimated by using Holter ECG in 12 healthy old volunteers (group I), 8 healthy young volunteers (group II), 8 young joggers (group III) and 10 old patients with hypertension medi-cating propranolol (group IV).

By repeated twice recordings of Holter ECG in ten subjects, minimal hourly heart rate (MHHR) at rest showed higher reproducibility and lower deviation than mean and maximum hourly heart rate. Sympathetic tone was predominant in the day time, whereas that of vagal tone was predominant at night. We estimated the autonomic nervous tone by comparing MHHR in the day time and at night.

MHHRs of group I in the day time and at night were 72±14BPM (mean±SD) and 62±12BPM, those of group II were 68±11BPM and 53±7BPM, group III were 54±7BPM and 41±3BPM and group IV were 57±9BPM and 51±7BPM, respectively.

At night MHHR was higher in group I than in group II. In the day time the difference of MHHR between group I and group II was lower than that at night. This result suggested both sympathetic and vagal tones were decreased by aging. The difference of MHHR between group II and group III at night was equal to that in the day time. MHHR was lower in group III than in group IV both in the day time and at night. These results suggested sympathetic tone of group III was almost equal to group II and difference of MHHR between group II and group III was due to the effect of predominant vagal tone.

To evaluate the alteration of MHHR was useful for the estimation of intrinsic autonomic nervous tone.