Regional variability of cerebral blood oxygenation response to hypercapnia

In functional magnetic resonance imaging studies changes in blood oxygenati on level-dependent (BOLD) signal intensities during task activation are rel ated to multiple physiological parameters such as cerebral blood how volume , and oxidative metabolism, as well as to the regional microvascular anatom y. Consequently, the magnitude of activation-induced BOLD signal changes ma y vary regionally and between subjects. The aim of this study was to use a uniform global stimulus such as hypercapnia to quantitatively investigate t he regional BOLD response in the human brain. In 10 healthy volunteers, T2* -weighted gradient echo images were acquired for a total dynamic scanning t ime of 9 min during alternating periods of breath holding for 30 s after ex piration and self-paced normal breathing for 60 s. Hypercapnia-induced BOLD signal changes in the sensorimotor cortex, frontal cortex, basal ganglia, visual cortex, and cerebellum were significantly different (P < 0.001) and varied from 1.8 to 5.1%. The highest BOLD signal changes were found in the cerebellum and visual cortex, whereas the lowest BOLD signal increase was o bserved in the frontal cortex. These results demonstrate a regional depende nce of the BOLD signal changes during breath hold-induced hypercapnia, indi rectly supporting the notion of regional different sensitivities of BOLD re sponses to task activation. (C) 1999 Academic Press.