title: The interaction of carbon dioxide and hypoxia in the control of cerebral blood flow.
abstract: Both hypoxia and carbon dioxide increase cerebral blood flow (CBF), and their effective interaction is currently thought to be additive. Our objective was to test this hypothesis. Eight healthy subjects breathed a series of progressively hypoxic gases at three levels of carbon dioxide. Middle cerebral artery velocity, as an index of CBF; partial pressures of carbon dioxide and oxygen and concentration of oxygen in arterial blood; and mean arterial blood pressure were monitored. The product of middle cerebral artery velocity and arterial concentration of oxygen was used as an index of cerebral oxygen delivery. Two-way repeated measures analyses of variance (rmANOVA) found a significant interaction of carbon dioxide and hypoxia factors for both CBF and cerebral oxygen delivery. Regression models using sigmoidal dependence on carbon dioxide and a rectangular hyperbolic dependence on hypoxia were fitted to the data to illustrate this interaction. We concluded that carbon dioxide and hypoxia act synergistically in their control of CBF so that the delivery of oxygen to the brain is enhanced during hypoxic hypercapnia and, although reduced during normoxic hypocapnia, can be restored to normal levels with progressive hypoxia.
authors.affiliation: Department of Physiology, University of Toronto, Toronto, ON, Canada, M5S 1A8.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Mardimae
authors.forename: Dahlia Y
authors.initials: DY
authors.lastname: Balaban
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Machina
authors.forename: Anne
authors.initials: A
authors.lastname: Battisti-Charbonney
authors.forename: Jay S
authors.initials: JS
authors.lastname: Han
authors.forename: Rita
authors.initials: R
authors.lastname: Katznelson
authors.forename: Leonid L
authors.initials: LL
authors.lastname: Minkovich
authors.forename: Ludwik
authors.initials: L
authors.lastname: Fedorko
authors.forename: Patricia M
authors.initials: PM
authors.lastname: Murphy
authors.forename: Marcin
authors.initials: M
authors.lastname: Wasowicz
authors.forename: Finola
authors.initials: F
authors.lastname: Naughton
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Meineri
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Fisher
authors.forename: James
authors.initials: J
authors.lastname: Duffin
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D001784:Blood Gas Analysis; D002245:Carbon Dioxide / Q000097:blood / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000097:blood / Q000503:physiopathology*; D001239:Inhalation; D008297:Male; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000502:physiology; D010100:Oxygen / Q000097:blood / Q000502:physiology; D012039:Regional Blood Flow / Q000502:physiology
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen