Facial cooling (FC) increases cerebral blood flow (CBF) at rest and during exercise; however, the mechanism of this response remains unclear. The purpose of the present study was to test our hypothesis that FC causes facial vasoconstriction that diverts skin blood flow (SkBF(face)) toward the middle cerebral artery (MCA V(mean)) at rest and to a greater extent during exercise. Nine healthy young subjects (20 ± 2 years) underwent 3 min of FC by fanning and spraying the face with a mist of cold water (~4°C) at rest and during steady-state exercise [heart rate (HR) of 120 bpm]. We focused on the difference between the averaged data acquired from 1 min immediately before FC and last 1 min of FC. SkBF(face), MCA V(mean), and mean arterial blood pressure (MAP) were higher during exercise than at rest. As hypothesized, FC decreased SkBF(face) at rest (-32 ± 4%) and to a greater extent during exercise (-64 ± 10%, P = 0.012). Although MCA V(mean) was increased by FC (Rest, +1.4 ± 0.5 cm/s; Exercise, +1.4 ± 0.6 cm/s), the amount of the FC-evoked changes in MCA V(mean) at rest and during exercise differed among subjects. In addition, changes in MCA V(mean) with FC did not correlate with concomitant changes in SkBF(face) (r = 0.095, P = 0.709). MAP was also increased by FC (Rest, +6.2 ± 1.4 mmHg; Exercise, +4.2 ± 1.2 mmHg). These findings suggest that the FC-induced increase in CBF during exercise could not be explained only by change in SkBF(face).
Keywords: diving reflex; external carotid artery; internal carotid artery; laser Doppler flowmetry; middle cerebral artery blood velocity.