Facial immersion in cold water enhances cerebral blood velocity during breath-hold exercise in humans

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Abstract
The diving response is initiated by apnea and facial immersion in cold water and includes, besides bradycardia, peripheral vasoconstriction, while cerebral perfusion may be enhanced. This study evaluated whether facial immersion in 10°C water has an independent influence on cerebral perfusion evaluated as the middle cerebral artery mean flow velocity (MCA Vmean) during exercise in nine male subjects. At rest, a breath hold of maximum duration increased the arterial carbon dioxide tension (PaCO2) from 4.2 to 6.7 kPa and MCA Vmean from 37 to 103 cm/s (mean; ∼178%; P < 0.001). Similarly, during 100-W exercise, a breath hold increased PaCO2 from 5.9 to 8.2 kPa ( P < 0.001) and MCA Vmean from 55 to 113 cm/s (∼105%), and facial immersion further increased MCA Vmean to 122 cm/s (∼88%; both P < 0.001). MCA Vmean also increased during 180-W exercise (from 47 to 53 cm/s), and this increment became larger with facial immersion (76 cm/s, ∼62%; P < 0.001), although PaCO2 did not significantly change. These results indicate that a breath hold diverts blood toward the brain with a >100% increase in MCA Vmean, largely because PaCO2 increases, but the increase in MCA Vmean becomes larger when combined with facial immersion in cold water independent of PaCO2.

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