Equilibrium disorders and R-R intervals in ECG

Vagal and sympathetic nerve activities influenced by posterior cerebral circulation in rabbits

Vagal and sympathetic nervous activities in the rabbit were recorded while vertebral blood flow was partially blocked by the injection of adenosine 5'-diphosphate (ADP; platelet aggregator). When a small dose of ADP (0.2 mg/kg) was administered into a unilateral vertebral artery, sympathetic nerve (SN) activity increased, and its magnitude was inversely correlated with the extent of the decrease in blood pressure (BP). A larger dose (2 mg/kg) of ADP suppressed SN activity on the injected side, whereas the change was small on the non-injected side. Vagal nerve (VN) activity showed a monophasic excitatory response on both sides, although the change was larger on the injected than on the non-injected side. As a result, asymmetry in autonomic nerve activity was more distinct in SN than in VN. The present study demonstrated that asymmetry of autonomic nervous function can result from changes in blood flow in the cerebellum and brainstem.

Cerebral autoregulation in patients with orthostatic hypotension

The present study was conducted to determine the relationship between autonomic nervous function and cerebral autoregulation in 17 patients with vertigo or dizziness. Autonomic nervous function was examined by measuring systolic blood pressure response and dynamic electrocardiogram R-peak to R-peak response upon standing up. Regional cerebral autoregulation was examined by comparing cerebral blood flow in both supine and standing positions with single photon emission computed tomography. Moreover, the relationship of each of these three measures to postural provocation of symptoms was studied. The findings indicated that autonomic nervous dysfunction does not influence cerebral autoregulation, but autonomic nervous dysfunction was related to postural provocation of symptoms. This might indicate that impaired autoregulation in the brain stem or the peripheral vestibule, which could not be detected by the single photon emission computed tomography, played a role in inducing vertigo or dizziness in patients with orthostatic hypotension.