Analysis of Role of Peripheral Vestibular Receptors on Orthostatic Tolerance using Heart Rate Variability in Rats

ABSTRACT

BACKGROUND: There is substantial evidence that the vestibular system is involved in the regulation of blood pressure. Heart rate variability (HRV) is useful to investigate the role of the peripheral vestibular receptors and the baroreceptors in the orthostatic tolerance. METHODS: EKG was recorded during postural changes with the head up either after sinoaortic denervation or after bilateral labyrinthectomies in Sprague-Dawley rats. HRV, including mean, standard deviation, coefficient of variation (CV), and power spectrum, were analyzed from R-R intervals of EKG. RESULTS: Phenylephrine increased low frequency region and sodium nitroprusside increased high frequency region in the power spectral analysis of HRV in anesthetized rats. Postural changes decreased blood pressure transiently and then increased blood pressure gradually in control rats, but the depression of blood pressure induced by postural change was greater in rats with both sinoaortic denervation and bilateral labyrinthectomies. The increase of CV of HRV just after sinoaortic denervation or bilateral labyrinthectomies represents an unstable heart rate in resting position, however, CV of HRV was increased markedly by postural change 7 days after bilateral labyrinthectomies. Postural change with sinoaortic denervation increased low-frequency region representing sympathetic activity, whereas bilateral labyrinthectomies increased highfrequency region representing parasympathetic activity in power spectral analysis. CONCLUSIONS: These results suggest that both the peripheral vestibular receptors and the baroreceptors have subsidiary action in orthostatic tolerance and the peripheral vestibular receptors regulate blood pressure during postural change through the sympathetic nervous system.