FLOW VELOCITY IN CAROTID-ARTERY IN HUMANS DURING IMMERSIONS AND UNDERWATER SWIMMING

Heart rate and flow velocity in the common carotid artery were examine d on eight subjects in various underwater conditions. The heart rate d ecreased more markedly during whole-body immersion than during head-ou t immersion. The end-diastolic flow velocity and the flow-velocity int egral in a cardiac cycle during whole-body immersion increased more ma rkedly than during head-out immersion. Differences in heart rate and f low velocity were not detected between sitting and prone positions in whole-body immersion. Heart rate increased at the beginning and after underwater swimming. The peak systolic flow velocity increased signifi cantly after the end of underwater swimming. The flow-velocity integra l in a cardiac cycle decreased during underwater swimming, but in a mi nute did not change significantly. These results suggest that facial i mmersion is important in eliciting pronounced carotid artery flow-velo city response in addition to the heart-rate response and that underwat er exercise influences these responses. However, underwater posture ap parently does not influence them.