title: Changes in human cerebral blood flow and cerebral blood volume during hypercapnia and hypocapnia measured by positron emission tomography.
abstract: Hypercapnia induces cerebral vasodilation and increases cerebral blood flow (CBF), and hypocapnia induces cerebral vasoconstriction and decreases CBF. The relation between changes in CBF and cerebral blood volume (CBV) during hypercapnia and hypocapnia in humans, however, is not clear. Both CBF and CBV were measured at rest and during hypercapnia and hypocapnia in nine healthy subjects by positron emission tomography. The vascular responses to hypercapnia in terms of CBF and CBV were 6.0 +/- 2.6%/mm Hg and 1.8 +/- 1.3%/mm Hg, respectively, and those to hypocapnia were -3.5 +/- 0.6%/mm Hg and -1.3 +/- 1.0%/mm Hg, respectively. The relation between CBF and CBV was CBV = 1.09 CBF0.29. The increase in CBF was greater than that in CBV during hypercapnia, indicating an increase in vascular blood velocity. The degree of decrease in CBF during hypocapnia was greater than that in CBV, indicating a decrease in vascular blood velocity. The relation between changes in CBF and CBV during hypercapnia was similar to that during neural activation; however, the relation during hypocapnia was different from that during neural deactivation observed in crossed cerebellar diaschisis. This suggests that augmentation of CBF and CBV might be governed by a similar microcirculatory mechanism between neural activation and hypercapnia, but diminution of CBF and CBV might be governed by a different mechanism between neural deactivation and hypocapnia.
authors.affiliation: Department of Radiology and Nuclear Medicine, Akita Research of Brain and Blood Vessels, Akita, Japan. hito@akita-noken.go.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ito
authors.forename: Iwao
authors.initials: I
authors.lastname: Kanno
authors.forename: Masanobu
authors.initials: M
authors.lastname: Ibaraki
authors.forename: Jun
authors.initials: J
authors.lastname: Hatazawa
authors.forename: Shuichi
authors.initials: S
authors.lastname: Miura
mesh_terms: D000328:Adult; D001810:Blood Volume / Q000502:physiology*; D002245:Carbon Dioxide / Q000097:blood; D002560:Cerebrovascular Circulation / Q000502:physiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006935:Hypercapnia / Q000000981:diagnostic imaging / Q000503:physiopathology*; D016857:Hypocapnia / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008297:Male; D010100:Oxygen / Q000097:blood; D014055:Tomography, Emission-Computed
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen