The Journal of Neurophysiology Vol. 86 No. 2 August 2001, pp. 559-564
Copyright ©2001 by the American Physiological Society

Noise-Enhanced Heart Rate and Sympathetic Nerve Responses to Oscillatory Lower Body Negative Pressure in Humans

 ¹Educational Physiology Laboratory, Graduate School of Education, The University of Tokyo, Tokyo 113-0033;  ²Cardiology Division, Saiseikai Futsukaichi Hospital, Fukuoka 818-8516; and  ³Research Institute of Angiocardiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan

Hidaka, Ichiro, Shin-Ichi Ando, Hideaki Shigematsu, Koji Sakai, Soko Setoguchi, Taku Seto, Yoshitaka Hirooka, Akira Takeshita, and Yoshiharu Yamamoto. Noise-Enhanced Heart Rate and Sympathetic Nerve Responses to Oscillatory Lower Body Negative Pressure in Humans. J. Neurophysiol. 86: 559-564, 2001. By injecting noise into the carotid sinus baroreceptors, we previously showed that heart rate (HR) responses to weak oscillatory tilt were enhanced via a mechanism known as "stochastic resonance." It remains unclear, however, whether the same responses would be observed when using oscillatory lower body negative pressure (LBNP), which would unload the cardiopulmonary baroreceptors with physically negligible effects on the arterial system. Also, the vasomotor sympathetic activity directly controlling peripheral resistance against hypotensive stimuli was not observed. We therefore investigated the effects of weak (0 to approximately 10 mmHg) oscillatory (0.03 Hz) LBNP on HR and muscle sympathetic nerve activity (MSNA) while adding incremental noise to the carotid sinus baroreceptors via a pneumatic neck chamber. The signal-to-noise ratio of HR, cardiac interbeat interval, and total MSNA were all significantly improved by increasing noise intensity, while there was no significant change in the arterial blood pressure in synchronized with the oscillatory LBNP. We conclude that the stochastic resonance, affecting both HR and MSNA, results from the interaction of noise with the signal in the brain stem, where the neuronal inputs from the arterial and cardiopulmonary baroreceptors first come together in the nucleus tractus solitarius. Also, these results indicate that the noise could induce functional improvement in human blood pressure regulatory system in overcoming given hypotensive stimuli.