Key result
Sympathetic stimulation via head-up tilt increased low-frequency cerebrovascular oscillations in controls and vasovagal syncope subjects (p<0.01), but this modulation was absent in diabetic patients.
Why the study?
Does sympathetic stimulation via head up tilt alter cerebrovascular and cardiovascular oscillations in healthy subjects, patients with vasovagal syncope, and patients with diabetes?
Observational (n=35)
Does sympathetic stimulation via head up tilt alter cerebrovascular and cardiovascular oscillations in healthy subjects, patients with vasovagal syncope, and patients with diabetes?
p-value: p=< 0.01
Cerebrovascular resistance vessels undergo autonomic modulation that precedes cardiovascular fluctuations, a mechanism that is blunted in patients with diabetes.
Blunted cerebrovascular autonomic modulation during tilt in diabetes may signal orthostatic vulnerability; hypothesis-generating and requires prospective validation before clinical application.
OBJECTIVE: To determine whether oscillations in the cerebrovascular circulation undergo autonomic modulation in the same way as cardiovascular oscillations. DESIGN: Cardiovascular and cerebrovascular oscillations were monitored at rest 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 velocity, arterial blood pressure, and heart rate. Coherence analysis was used to study the association between each pair of oscillations. Phase analysis showed the delay of the oscillations in the cardiovascular signals with respect to the cerebrovascular signals. RESULTS: The power in the sympathetic (LF) components in all the oscillations increased during head up tilt (p < 0.01) in the controls and in the subjects with vasovagal syncope, but not in patients with diabetes. Significant coherence (> 0.5) in the LF band was present between cerebrovascular and cardiovascular oscillations in most of the controls and in subjects with vasovagal syncope, but not in the diabetic patients (< 50% of the patients). In the LF band, cerebrovascular oscillations preceded the cardiovascular oscillations (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 precede the resulting fluctuations in other cardiovascular signals. Autonomic neuropathy and microvascular stiffness in diabetic patients reduces this modulation.
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Cencetti et al. (1999) conducted an observational in Vasovagal syncope and complicated non-insulin dependent diabetes mellitus (n=35). Sympathetic stimulation (head up tilt) vs. Rest was evaluated on Power in the sympathetic (LF) components of cerebrovascular and cardiovascular oscillations (p=< 0.01). Sympathetic stimulation via head-up tilt increased low-frequency cerebrovascular oscillations in controls and vasovagal syncope subjects (p<0.01), but this modulation was absent in diabetic patients.
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