The effects of graded hypercapnia on the activation flow coupling response due to forepaw stimulation in alpha-chloralose anesthetized rats.

Activation flow coupling (AFC), changes in cerebral blood flow (CBF) due to changes in neural activity with functional stimulation, provides the physiological basis of many neuroimaging techniques. Hypercapnia leads to an increase in CBF while neural activity remains unaffected. Laser Doppler (LD) flowmetry was used to measure CBF changes (LD(CBF)) in the somatosensory cortex due to periodic electrical forepaw stimulation (4 s in duration) before and during graded hypercapnia (3% CO(2), 5% CO(2) and 10% CO(2)). With increasing CO(2) concentrations, the baseline LD(CBF) progressively increased. The peak height (PH) of the LD(CBF) response, expressed as a percent change from the observed baseline for each hypercapnic state, significantly decreased (P<0.05) with increasing CO(2) concentrations. However, the absolute magnitude of the LD(CBF) change was independent of CO(2) concentration. The temporal dynamics of the LD(CBF) response during hypercapnia were significantly prolonged compared to baseline conditions (P<0.05).