Blood flow velocity in common carotid artery in humans during breath- holding and face immersion

Blood flow velocity was measured in the common carotid artery of humans during breath-holding (BH) in the supine and upright positions, and during breath-hold face immersion (FIBH) in cold (20°C) and warm (35°C) water in the upright position with 90° flexion of the upper body, to test the influences of the body position, facial immersion and temperature on changes in cerebral blood flow. Simultaneously, the heart rate (HR) and blood pressure (BP) under the same conditions, and the end-tidal PO₂ and PCO₂ (PETO₂ and PETCO₂) during supine BH, were also measured. Results showed that posture had no significant effect on the apneic HR. Bradycardia developed during cold FIBH, but not warm FIBH. The BP increased during BH in both positions, and during both cold and warm FIBH. The PETO₂ decreased and the PETCO₂ increased significantly at the end of BH. The blood velocity decreased transiently at the beginning of upright BH, but increased time- dependently during both supine and upright BH. Moreover, the velocity increased more during warm FIBH than during BH's, and even more during cold than warm FIBH. When bradycardia occurred during cold FIBH, the velocity integral per minute tended to decrease. These results suggest that the cerebral blood flow increases in these conditions of BH. This increase can be explained by the increase in PETCO₂ and decrease in PETO₂, possibly with a slight contribution from the increase in the BP. However, the more marked increases in blood velocity during warm and cold FIBH must also involve reflex effects of facial immersion and cold stimulation. We conclude that facial immersion and cold stimulation influence the HR and cerebral blood flow, but that posture has little, if any, effect on the HR, BP, or the cerebral blood flow.