Regional hypoxic cerebral vasodilation facilitated by diameter changes primarily in anterior versus posterior circulation

The inability to quantify cerebral blood flow and changes in macrocirculation cross-sectional area in all brain regions impedes robust insight into hypoxic cerebral blood flow control. We applied four-dimensional flow magnetic resonance imaging to quantify cerebral blood flow (ml center dot min(-1)) and cross-sectional area (mm(2)) simultaneously in 11 arteries. In healthy adults, blood pressure, O-2 Saturation (SpO(2)), and end-tidal CO2 were measured at baseline and steady-state hypoxia (FiO(2) = 0.11). We investigated left and right: internal carotid, vertebral, middle, anterior, posterior cerebral arteries, and basilar artery. Hypoxia (SpO(2) = 80 +/- 2%) increased total cerebral blood flow from 621 +/- 38 to 742 +/- 50ml center dot min(-1) (p<0.05). Hypoxia increased cerebral blood flow, except in the right posterior cerebral arteries. Hypoxia increased cross-sectional area in the anterior arteries (left and right internal carotid arteries, left and right middle, p<0.05; left and right anterior p = 0.08) but only the right vertebral artery of the posterior circulation. Nonetheless, relative cerebral blood flow distribution and vascular reactivity (%cerebral blood flow center dot SpO(2)(-1)) were not different between arteries. Collectively, moderate hypoxia: (1) increased cerebral blood flow, but relative distribution remains similar to normoxia, (2) evokes similar vascular reactivity between 11 arteries, and (3) increased cross-sectional area primarily in the anterior arteries. This study provides the first wide-ranging, quantitative, functional and structural data regarding intracranial arteries during hypoxia in humans, highlighting cerebral blood flow regulation of microcirculation and macrocirculation differs between anterior and posterior circulation.