The effects of graded hypercapnia on the activation flow coupling response due to forepaw stimulation in α-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% CO₂, 5% CO₂ and 10% CO₂). With increasing CO₂ 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 CO₂ concentrations. However, the absolute magnitude of the LD_CBF change was independent of CO₂ concentration. The temporal dynamics of the LD_CBF response during hypercapnia were significantly prolonged compared to baseline conditions (P<0.05).