Regional variability of cerebral blood oxygenation response to hypercapnia.

In functional magnetic resonance imaging studies changes in blood oxygenation level-dependent (BOLD) signal intensities during task activation are related to multiple physiological parameters such as cerebral blood flow, volume, and oxidative metabolism, as well as to the regional microvascular anatomy. Consequently, the magnitude of activation-induced BOLD signal changes may vary regionally and between subjects. The aim of this study was to use a uniform global stimulus such as hypercapnia to quantitatively investigate the regional BOLD response in the human brain. In 10 healthy volunteers, T2*-weighted gradient echo images were acquired for a total dynamic scanning time of 9 min during alternating periods of breath holding for 30 s after expiration 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 observed in the frontal cortex. These results demonstrate a regional dependence of the BOLD signal changes during breath hold-induced hypercapnia, indirectly supporting the notion of regional different sensitivities of BOLD responses to task activation.