The effect of an acute increase in central blood volume on the response of cerebral blood flow to acute hypotension

• Published in: Journal of applied physiology (1985) Vol. 119; no. 5; pp. 527 - 533
• Main Authors: Ogoh, Shigehiko, Hirasawa, Ai, Sugawara, Jun, Nakahara, Hidehiro, Ueda, Shinya, Shoemaker, J Kevin, Miyamoto, Tadayoshi
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01.09.2015
• Subjects: Adult; Blood Flow Velocity - physiology; Blood pressure; Blood Pressure - physiology; Blood Volume - physiology; Cerebrovascular Circulation - physiology; Female; Heart Rate - physiology; Homeostasis - physiology; Humans; Hypercapnia - physiopathology; Hypotension - physiopathology; Lower Body Negative Pressure - methods; Male; Middle Cerebral Artery - physiology; Muscular system; Veins & arteries; cardiac output; dynamic regulation; arterial pressure; transcranial Doppler; humans
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00277.2015

The purpose of the present study was to examine whether the response of cerebral blood flow to an acute change in perfusion pressure is modified by an acute increase in central blood volume. Nine young, healthy subjects voluntarily participated in this study. To measure dynamic cerebral autoregulation during normocapnic and hypercapnic (5%) conditions, the change in middle cerebral artery mean blood flow velocity was analyzed during acute hypotension caused by two methods: 1) thigh-cuff occlusion release (without change in central blood volume); and 2) during the recovery phase immediately following release of lower body negative pressure (LBNP; -50 mmHg) that initiated an acute increase in central blood volume. In the thigh-cuff occlusion release protocol, as expected, hypercapnia decreased the rate of regulation, as an index of dynamic cerebral autoregulation (0.236 ± 0.018 and 0.167 ± 0.025 s(-1), P = 0.024). Compared with the cuff-occlusion release, the acute increase in central blood volume (relative to the LBNP condition) with LBNP release attenuated dynamic cerebral autoregulation (P = 0.009). Therefore, the hypercapnia-induced attenuation of dynamic cerebral autoregulation was not observed in the LBNP release protocol (P = 0.574). These findings suggest that an acute change in systemic blood distribution modifies dynamic cerebral autoregulation during acute hypotension.