Autonomic control of the cerebral circulation during normal and impaired peripheral circulatory control

Objective-To determine whether oscillations in the cerebrovascular circulat ion undergo autonomic modulation in the same way as cardiovascular oscillat ions. Design-Cardiovascular and cerebrovascular oscillations were monitored at re st and during sympathetic stimulation (head up tilt). The association with and transmission of the oscillations in the sympathetic (low frequency, LF) and respiratory (high frequency, HF) bands was assessed. Subjects-13 healthy volunteers, 10 subjects with vasovagal syncope, and 12 patients with complicated non-insulin dependent diabetes mellitus. Main outcome measures-Power spectrum analysis of cerebral blood flow veloci ty, arterial blood pressure, and heart rate. Coherence analysis was used to study the association between each pair of oscillations. Phase analysis sh owed the delay of the oscillations in the cardiovascular signals with respe ct to the cerebrovascular signals. Results-The power in the sympathetic (LF) components in all the oscillation s increased during head up tilt (p < 0.01) in the controls and in the subje cts with vasovagal syncope, but not in patients with diabetes. Significant coherence (> 0.5) in the LF band was present between cerebrovascular and ca rdiovascular oscillations in most of the controls and in subjects with vaso vagal syncope, but not in the diabetic patients (< 50% of the patients). In the LF band, cerebrovascular oscillations preceded the cardiovascular osci llations (p < 0.05) at rest in all groups: the phase shifts were reduced (p < 0.05) during head up tilt for all cardiovascular signals in healthy and syncopal subjects, but only for heart rate in diabetic patients. Conclusions-The cerebrovascular resistance vessels are subject to autonomic modulation; low frequency oscillations in cerebral blood flow velocity pre cede the resulting fluctuations in other cardiovascular signals. Autonomic neuropathy and microvascular stiffness in diabetic patients reduces this mo dulation.