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Effects of Ageing on Gross and Cortical Cerebral Autoregulatory Upper Limits
Author(s) -
Thompson Emma,
Coney Andrew,
Marshall Janice
Publication year - 2015
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.29.1_supplement.645.8
Subject(s) - cerebral blood flow , phenylephrine , vasoconstriction , cerebral circulation , medicine , vasodilation , ageing , autoregulation , endocrinology , blood pressure
Ageing leads to impaired endothelium‐dependent vasodilatation and sympathetically‐mediated vasoconstriction in many tissues including brain. We hypothesised cerebral autoregulation is modulated by these influences and ageing is associated with impaired autoregulation at the upper limit (UL). In anaesthetised young (Y) male Wistar rats (6‐8 weeks, n=25), basal arterial blood pressure (ABP) was 127±2mmHg, whereas in old (O) rats (52‐58 weeks, n=12), ABP was 148±2mmHg* (*=P<0.05). Phenylephrine was infused (0.1–200µg/kg/min i.v.) to raise ABP and gross cerebral blood flow (CBF) was recorded from common carotid after external carotid ligation. Dual‐line linear regression of gross CBF vs ABP, gave an UL for Y rats of 168±2mmHg. In 8 Y rats, cortical red cell flux (cRCF) was simultaneously monitored by laser speckle imaging; in these, gross CBF UL was 166±4mmHg, but cCBF UL was higher at 170±5mmHg*. By contrast in O rats, gross CBF UL was 180±3mmHg * (vs Y rats), and cCBF UL was 179±1mmHg (NS vs gross CBF UL in O rats, or cCBF UL in Y rats). We suggest in Y rats, a higher UL for cCBF vs gross CBF reflects further capacity for autoregulatory constriction of smaller cerebral vessels even when larger, proximal vessels have reached their UL. This may protect cortical tissue circulation. Since O rats were hypertensive compared to Y rats and hypertension has been shown to increase the UL, this may explain the higher gross CBF UL in O rats. However, as the UL for cCBF and gross CBF were similar in O rats, it seems the extended autoregulatory range for smaller cerebral vessels is lost with ageing. This could result in fragile cortical vessels being exposed to increased pressure when ABP rises and increase the risk of haemorrhagic stroke. British Heart Foundation funding is gratefully acknowledged.