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

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 V_mean) during exercise in nine male subjects. At rest, a breath hold of maximum duration increased the arterial carbon dioxide tension (Pa_CO2) from 4.2 to 6.7 kPa and MCA V_mean from 37 to 103 cm/s (mean; ∼178%; P < 0.001). Similarly, during 100-W exercise, a breath hold increased Pa_CO2 from 5.9 to 8.2 kPa (P < 0.001) and MCA V_mean from 55 to 113 cm/s (∼105%), and facial immersion further increased MCA V_mean to 122 cm/s (∼88%; both P < 0.001). MCA V_mean also increased during 180-W exercise (from 47 to 53 cmls), and this increment became larger with facial immersion (76 cm/s, ∼62%; P < 0.001), although Pa_CO2 did not significantly change. These results indicate that a breath hold diverts blood toward the brain with a >100% increase in MCA V_mean, largely because Pa_CO2 increases, but the increase in MCA V_mean becomes larger when combined with facial immersion in cold water independent of Pa_CO2. [ABSTRACT FROM AUTHOR]