Effect of Aging on Dynamic Cerebral Autoregulation During Head-Up Tilt

Abstract

Background and Purpose-Physiological aging is associated with many changes in the cardiovascular and cerebrovascular systems, but dynamic cerebral autoregulation (CA) during supine rest shows no age-related changes. Because syncopal syndromes usually occur during orthostatic stress and their prevalence increases with age, it is important to define the effect of aging on dynamic CA during orthostatic stress. Methods-Twenty-five younger subjects (Յ40 years) and 25 sex-matched older subjects (Ն60 years) underwent 70°h ead-up tilt for 30 minutes. Bilateral middle cerebral artery blood flow velocities were measured with transcranial Doppler ultrasound, along with noninvasive continuous measurements of arterial blood pressure, heart rate, and transcutaneous and end-tidal carbon dioxide concentrations. By comparing actual changes in cerebral blood flow velocity to changes predicted by a model based on arterial blood pressure changes, we derived dynamic autoregulatory indexes for each subject for periods before, during, and after tilt. Results-Younger subjects were a mean of 40 years younger than older subjects (28Ϯ8 versus 69Ϯ10 years). Although cerebral blood flow velocity (PϽ0.001) and baroreceptor sensitivity (PϽ0.001) were significantly lower at rest in older subjects, autoregulatory indexes were similar in younger and older subjects at all times before, during, and after tilt (Pϭ0.62). Conclusions-Although increasing age is associated with lower cardiac baroreceptor sensitivity and cerebral blood flow velocity, dynamic CA during orthostatic stress is unaffected by physiological aging.

Altered phase interactions between spontaneous blood pressure and flow fluctuations in type 2 diabetes mellitus: Nonlinear assessment of cerebral autoregulation

“…2 diabetic subjects had autonomic dysfunction with orthostatic hypotension and 8 diabetes subjects also had cardiac-vagal impairment. Diabetic subjects were treated with insulin (4), oral glucose-control agents (9) or diet (7). In 6 hypertensive diabetic subjects, antihypertensive medications were discontinued for 3 days prior to the study.…”

“…Cerebral autoregulation dynamics are usually evaluated by the changes in BFV and BP during the interventions that induce rapid BP reductions or increases such as the Valsalva maneuver, thigh cuff deflation and the head-up tilt [2,9,50,[60][61][62][63]. The conventional approach is valuable, because it allows assessments of the autoregulation responses during rapid variations in systemic pressure under the stressed conditions.…”

“…Conventional approaches model autoregulation with blood pressure as input and blood flow as output [8,9]. A transfer function is typically used to explore the relationship between blood pressure (BP) and blood flow velocity (BFV) by calculating gain and phase shift between the BP and BFV power spectra [2,8,[10][11][12][13][14][15][16].…”

Nonlinear Assessment of Cerebral Autoregulation from Spontaneous Blood Pressure and Cerebral Blood Flow Fluctuations

“…Reliable and noninvasive assessment of cerebral autoregulation is a major challenge in medical diagnostics and post-stroke care. Conventional approaches model autoregulation with BP as input and blood flow as output (using blood flow velocity (BFV) measured by transcranial Doppler ultrasound and beat-to-beat peripheral BP) (Diehl et al 1995(Diehl et al , 1998Olufsen et al 2002;Carey et al 2003) and assume that signals are composed of superimposed sinusoidal oscillations of constant amplitude and period at a presumed frequency range. However, BP and BFV signals recorded in clinical settings are often nonstationary, and are modulated by nonlinearly interacting processes at multiple time-scales corresponding to the beat-to-beat systolic pressure, respiration, spontaneous BP fluctuations, and those induced by interventions.…”

“…Traditional approaches assess autoregulatory responses by challenging cerebrovascular systems using interventions such as the Valsalva maneuver, thigh cuff deflation and the head-up tilt (Carey et al 2003;Panerai 1998;Novak et al 1998;Tiecks et al 1999;Dawson et al 1999;Panerai et al 2001;Novak et al 2003). These intervention procedures induce large intracranial pressure fluctuations and require patients' cooperation and, therefore, such procedures are limited for clinical evaluation of autoregulation.…”