Assessing cerebrovascular autoregulation from critical closing pressure and resistance area product during upright posture in aging and hypertension

Abstract

Robertson AD, Edgell H, Hughson RL. Assessing cerebrovascular autoregulation from critical closing pressure and resistance area product during upright posture in aging and hypertension. Am J Physiol Heart Circ Physiol 307: H124 -H133, 2014. First published May 23, 2014 doi:10.1152/ajpheart.00086.2014.-Static cerebral autoregulation (sCA) is believed to be resistant to aging and hypertensive pathology. However, methods to characterize autoregulation commonly rely on beat-by-beat mean hemodynamic measures and do not consider within-beat pulse wave characteristics that are impacted by arterial stiffening. We examined the role of critical closing pressure (CrCP) and resistance area product (RAP), two measures derived from the pulse wave, across supine lying, sitting, and standing postures in young adults, normotensive older adults, and older adults with controlled and uncontrolled hypertension (N ϭ 80). Traditional measures of sCA, using both intracranial and extracranial methods, indicated similar efficiency across all groups, but within-beat measures suggested different mechanisms of regulation. At rest, RAP was increased in hypertension compared with young adults (P Ͻ 0.001), but CrCP was similar. In contrast, the drop in CrCP was the primary regulator of change in cerebrovascular resistance upon adopting an upright posture. Both CrCP and RAP demonstrated group-by-posture interaction effects (P Ͻ 0.05), with older hypertensive adults exhibiting a rise in RAP that was absent in other groups. The posturerelated swings in CrCP and RAP were related to changes in both the pulsatile and mean components of arterial pressure, independent of age, cardiac output, and carbon dioxide. Group-by-posture differences in pulse pressure were mediated in part by an attenuated heart rate response in older hypertensive adults (P ϭ 0.002). Examination of pulsatile measures in young, elderly, and hypertensive adults identified unique differences in how cerebral blood flow is regulated in upright posture. middle cerebral artery; carotid arteries; Doppler ultrasound; pulse pressure ORTHOSTATIC INTOLERANCE is a primary contributing factor to hospitalizations of older adults, with syncope being a prevalent trigger for admittance to emergency departments (46). Syncope and falls are often precipitated by symptoms of cerebral hypoperfusion, including dizziness and confusion (39). Even in young adults, cerebral blood flow (CBF) is lower when sitting or standing compared with lying supine (33, 41). Hence, a lower resting CBF, as observed in aging and hypertension (6), increases the risk for transient hypoperfusion in upright postures and emphasizes the need for effective cerebrovascular control. Cerebral autoregulation (CA) characterizes the efficiency in maintaining CBF despite changes in arterial blood pressure (ABP) (48) and is commonly assessed by the change in cerebrovascular resistance (CVR) for a given change in pressure (21,26,48). When considering CVR as the solitary regulator (i.e., CVR ϭ ABP/CBF), CA has proven to be a robust physio...

Does gradual change in head positioning affect cerebrovascular physiology?

“…This contrasts with a previous report by Robertson et al. () who found a nonsignificant rise in RAP but significant CrCP reduction, particularly in healthy older adults during upright posture, suggesting that CrCP played a dominant role in response to posture change. Castro et al.…”

Cerebral hemodynamics in orthostatic intolerance with normal head-up tilt test

“…Mean arterial pressure was calculated by the following formula: MAP = (BPsys + 2*BPdia)/3 (MAP, mean arterial pressure; BP sys, systolic blood pressure; BPdia, diastolic blood pressure). Cerebral critical closing pressure was calculated by according to a method that has previously been reported and is based on linear regression of CBFV and arterial blood pressure . We calculated the CCP according to the following formula: CCP = BPsys−[BFVsys*(BPsys−BPdia)/(BFVsys−BFVdia)] (CCP, cerebral critical closing pressure; BFVsys, systolic flow velocity of middle cerebral artery (MCA); and BFVdia, diastolic flow velocity of MCA).…”

“…Transcranial Doppler (TCD) has been widely used as a tool to assess the hemodynamic changes in OI patients because of the characteristics of real‐time scan, low cost, non‐invasiveness, continuous monitoring, frequent and repeated measurement, and good accessibility although various neuroimaging techniques such as cerebral angiography, functional CT or MR scans, perfusion CT or MR scans, SPECT, and PET scan can also be used in evaluating the cerebral hemodynamic state . Several parameters including cerebral blood flow, cerebral vascular resistance (CVR), pulsatile index, and CCP and several maneuvers including breath holding, add of vasodilator agents, Valsalva maneuver, and lower body negative pressure have been be used in various investigations with TCD . Although the pathophysiology of OI was known as cerebral hypoperfusion in upright position, studies using TCD and HUT tests exhibited the variable results according to the enrolled patients and methods of HUT and TCD tests.…”

Neurovascular coupling in humans: Physiology, methodological advances and clinical implications

“…Describes how much perfusion pressure increases or decreases for a given change in cerebral blood flow. 145,146 CCP MAP -(vmean  RAP) The instantaneous (i.e., over a single heart beat) theoretical perfusion pressure at which cerebral blood flow ceases (i.e., becomes zero). Generally calculated as the pressure corresponding to zero cerebral blood flow when calculating the instantaneous relationship between blood pressure and cerebral blood flow.…”

“…This value is generally above zero due to significant collapsing forces exerted on the vasculature from intracranial pressure and tension within the vessel walls themselves. [145][146][147] PI (vmax-vmin)/vmean Ratio of cerebral pulsatile blood flow to average cerebral blood flow. This is considered to be related to small cerebral vessel elasticity and tone.…”