Effect of cold face stimulation on cerebral blood flow in humans

BACKGROUND AND PURPOSE: In humans, activation of the diving reflex by a cold stimulus to the face results in bradycardia, peripheral vasoconstriction and an increase in blood pressure. However, responses of the cerebral blood flow have not yet been evaluated. We undertook this study to assess the effect of cold face stimulation on the cerebral circulation in humans. METHODS: Seventeen healthy volunteers, aged 27+/-5 years were evaluated during application of a cold stimulus (0 degrees C) to the forehead for 60s. We continuously monitored mean arterial pressure (MAP), mean flow velocity (MFV) of the middle cerebral artery, cardiac output, skin blood flow, heart rate and end-tidal CO2. Total peripheral resistance (TPR) was calculated as MAP divided by cardiac output. Cerebrovascular resistance index (CVRi) was calculated as MAP divided by MFV. RESULTS: Cold face stimulation did not significantly affect cardiac output but resulted in significant decreases in heart rate and skin blood flow and an increase in MAP. MFV in the mid-cerebral artery showed a slight, but significant increase. The maximum increase in CVRi (14.2+/-11.4%) was significantly (P<0.01) less than the maximum increase in TPR (23.9+/-5.7%). End-tidal CO2 did not change significantly during the cold stimulation. CONCLUSIONS: In contrast to other sympathetic stimulations (e.g. lower body negative pressure), facial cooling results in an increase in cerebral blood flow. The amount of cerebral vasoconstriction was less than the amount of total peripheral vasoconstriction. These results suggest that although there is some constriction of the cerebral resistance vessels during cold face stimulation, cerebral perfusion was maintained, possibly by opposing parasympathetic activation.