A two-years trend in the recovery speed of heart rate during bathing stress

The heart rate (HR) of a healthy male adult was recorded while taking a hot water bath. The recovery speed following the initial overshoot of the HR was calculated almost every other day over a period of two years. Immediately after immersion in the tub, the HR reached a peak within 20 seconds and then exponentially decreased toward the lowest rate in the 120 seconds of bathing. This initial overshoot and the exponential recovery were observed not only in normal subjects but also in patients of atrial fibrillation. It was found that the initial recovery speed of the HR from the stress of bathing had a specific rhythm in the subject. The spectrum analysis of the speed series by the maximum entropy method indicated that slow recovery speed appeared in major cyclic periods of one year and approximately one month. This daily stress test may play a potential role in a chronodiagnostic approach to the autonomic nerve mediated cardiovascular system