title: The effect of an acute increase in central blood volume on the response of cerebral blood flow to acute hypotension.
abstract: 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.
authors.affiliation: Toyo University, Saitama, Japan; ogoh@toyo.jp.
authors.forename: Shigehiko
authors.initials: S
authors.lastname: Ogoh
authors.affiliation: Toyo University, Saitama, Japan;
authors.forename: Ai
authors.initials: A
authors.lastname: Hirasawa
authors.affiliation: National Institute of Advanced Industrial Science and Technology, Ibaraki Japan;
authors.forename: Jun
authors.initials: J
authors.lastname: Sugawara
authors.affiliation: Morinomiya University of Medical Sciences, Osaka, Japan; and.
authors.forename: Hidehiro
authors.initials: H
authors.lastname: Nakahara
authors.affiliation: Morinomiya University of Medical Sciences, Osaka, Japan; and.
authors.forename: Shinya
authors.initials: S
authors.lastname: Ueda
authors.affiliation: Western University, London, Ontario, Canada.
authors.forename: J Kevin
authors.initials: JK
authors.lastname: Shoemaker
authors.affiliation: Morinomiya University of Medical Sciences, Osaka, Japan; and.
authors.forename: Tadayoshi
authors.initials: T
authors.lastname: Miyamoto
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D001810:Blood Volume / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology; D007022:Hypotension / Q000503:physiopathology*; D008150:Lower Body Negative Pressure / Q000379:methods; D008297:Male; D020768:Middle Cerebral Artery / Q000502:physiology
keywords: arterial pressure; cardiac output; dynamic regulation; humans; transcranial Doppler