Permissive hypercapnia is commonly used as vasodilatory challenge in clinical applications and basic research. During fMRI experiments continuous exposure to mild (3-10%) CO2 can be applied to derive stimulus induced changes in the cerebral rate of oxygen consumption (CMRO2) by measuring cerebral blood flow and blood oxygenation dependent (BOLD) signal. Previous data from anesthetized primate during hypercapnia suggested increase in CBF are accompanied by decreases in neuronal activity. In this context, using multinuclear (31P/1H) and multi-parametric MR we show that mild exposure to hypercapnia elevates regional CBF, and can cause marginal but consistent drop in intracellular pH of rat brain, despite constant [ADP ~25-35µM] and [ATP ~3-2.4mM] to that of resting brain. Our findings support the view that unspecific drop in brain pH may likely elevate regional CBF, thereby sustain oxygen supply-to-demand ratio in rat brain.
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