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

Abstract

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 stiVness in diabetic patients reduces this modulation. (Heart 1999;82:365-372)

Altered cerebral regulation in type 2 diabetic patients with cardiac autonomic neuropathy

“…The phase shift results in our study are at slight variance with the results reported by Cencetti et al [23]. During head-up tilt, Cencetti et al observed a significant reduction in phase shift in their controls [23].…”

“…During head-up tilt, Cencetti et al observed a significant reduction in phase shift in their controls [23]. This shortening of phase shift was ascribed to sympathetic activation and subsequent sympathetically mediated vessel stiffening [23].…”

Continuous vs. interval exercise training in hypertensive subjects

“…This 'stretching' could then reverse the glycation-related collagen crosslinking that is responsible for reduced arterial compliance. 7 Increases in the amount of collegen in the arterial wall, hypertrophy of the smooth muscle present in arterial walls and dysfunction of the endothelium have also been hypothesized to underlie increases in arterial stiffness in older adults with hypertension, 7 although the role of exercise in reversing these mechanisms remains uncertain.…”

High fitness is associated with a better cardiovascular risk profile in patients with type 2 diabetes mellitus

“…20 It has been hypothesized that pulsatile stretching of collagen fibers during aerobic exercise could break the collagen links and result in decreased arterial stiffness. 21 However, the impact of aerobic exercise on arterial stiffness in diabetic patients is still uncertain. A 3-month study with 36 elderly diabetic patients randomized to aerobic or anaerobic exercise showed a reduction in arterial stiffness in the aerobic group, 8 whereas another study with 50 patients randomized to exercise training or standard treatment did not show any change in aortic stiffness after a 24-month program.…”