• H Ito, I Kanno, M Ibaraki, T Suhara, and S Miura.
• Department of Radiology and Nuclear Medicine, Akita Research Institute of Brain and Blood Vessels, Akita, Japan. hito@nirs.go.jp
• Acta Physiol (Oxf). 2008 Aug 1; 193 (4): 325-30.

AimInter-individual variations in normal human cerebral blood flow (CBF) at rest condition have been reported. Inter-individual variation of cerebral vascular tone is considered to contribute to this, and several determinants of cerebral vascular tone have been proposed. In the present study, the relationship between CBF and cerebral vascular tone to inter-individual variation at rest condition was investigated using positron emission tomography (PET).MethodsCBF was measured using PET with H(2) (15)O in each of 20 healthy subjects (20-28 years) under three conditions: at rest (baseline), during hypercapnia and during hypocapnia. The vascular response to change in P(a)CO(2) was calculated as the percentage changes in CBF per absolute change in P(a)CO(2) in response to hypercapnia and hypocapnia.ResultsA significant negative correlation between baseline CBF and the vascular response to hypocapnia was observed in the thalamus, temporal cortex, parietal cortex, occipital cortex and cerebral cortex (P < 0.05). A trend towards negative correlation between baseline CBF and the vascular response to hypocapnia was observed in the cerebellum and putamen (P < 0.1). A significant negative correlation between baseline CBF and the vascular response to hypercapnia was observed in the occipital cortex (P < 0.05). No significant correlation was observed between baseline CBF and haemoglobin concentration, and P(a)CO(2).ConclusionThese findings support the assumption that cerebral vascular tone might incline towards vasoconstriction and vasodilatation when baseline CBF is low and high between individuals respectively. Although several determinants of cerebral vascular tone have been proposed, the mechanism of such inter-individual differences in cerebral vascular tone is unknown.

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