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

Andrew D. Robertson, Heather Edgell, Richard L. Hughson
2014 American Journal of Physiology. Heart and Circulatory Physiology  
Robertson AD, Edgell H, Hughson RL. Assessing cerebrovascular autoregulation from critical closing pressure and resistance area product during upright posture in aging and hypertension. 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
more » ... ined 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 pos-Address for reprint requests and other correspondence: Values are group means Ϯ SD. Technical limitations limited sample sizes in YNG/OLD/cHTN/uHTN to 23/17/21/10 for MBFICA and CVRICA, and to 6/10/12/5 for CrCPICA and RAPICA. P value determined by one-way ANOVA across groups. H129 CBF AND POSTURE IN AGING AND HYPERTENSION AJP-Heart Circ Physiol •
doi:10.1152/ajpheart.00086.2014 pmid:24858843 fatcat:gd2pvbd6rrfwvkrdyd3hwycu3u