Effects of Weak External Mechanical Force Stimulation on the Heart Rate Variability of Rats

Motivation: The heartbeat is driven by electric signals generated inside the heart, the cardiac conducting system plays an important role. Although there are pharmacological and electrical methods working on this conducting system, effect of mechanical stimulation has rarely been discussed. Methods: We used waterbed (size 60×40×10 cm) as a media to study the heart rate variability (HRV) affected by beating the bed with weak mechanical force with 0.5-mm-Hg amplitude. The waterbed is specially designed to raise the transmission efficiency for sound wave. Results: Among 7 studies on 5 rats, there were almost no changes in diastolic pressure, systolic pressure and heart rate, but average of CV (coefficient of variance) of 15-minute heart rate sequences increased from the control value 0.0098±0.0023 (mean±SD) to 0.0119±0.0032 (mean±SD) during the stimulation and decreased to 0.0078±0.0020 (mean±SD) in 15 minutes after the stimulation [p values (paired t-test, both compared with the control) < 0.006 and < 0.0007 respectively]. Discussion: Here we show that such a weak mechanical stimulation was sufficient to affect the circulatory system. Since the effect is not directly acting on the conducting system, this small power may influence the arterial system through resonance mechanism.