Blood flow in the carotid artery during breath-holding in relation to diving bradycardia

Abstract

The present study investigated the mechanism of diving bradycardia. A group of 14 healthy untrained male subjects were examined during breath-holding either out of the water (30-33 degrees C), in heat-out immersion, or in whole-body submersion (27-29 degrees C) in a diving pool. Blood velocity, blood volume flow in the carotid artery, diastolic blood pressure and electrocardiogram were measured and recorded during the experiments. The peak blood velocity increased by 13.6% (P < 0.01) and R-wave amplitude increased by 57.1% (P < 0.005) when the subjects entered water from air. End-diastolic blood velocity (Ved) in the carotid artery increased significantly during breath-holding, e.g. Ved increased from 0.20 (SD 0.02) m.s-1 at rest to 0.33 (SD 0.04) m.s-1 (P < 0.001) at 50.0 s in breath-hold submersion to a 2.0-m depth. Blood volume flow in the carotid artery increased by 26.6% (P < 0.05) at 30 s and 36.6% (P < 0.001) at 40 s in breath-hold submersion to a 2.0-m depth. Diastolic blood pressure increased by 15.4% (P < 0.01) at 60 s during breath-holding in head-out immersion. Blood volume flow, Ved and diastolic blood pressure increased significantly more and faster during breath-holding in submersion than out of the water. There was a good negative correlation with the heart rate: the root mean square correlation coefficient r was 0.73 (P < 0.001). It was concluded that an increased accumulation of blood in the aorta and arteries at end-diastole and decreased venous return, caused by an increase in systemic peripheral resistance during breath-holding, underlies diving bradycardia.

The human diving response, its function, and its control

“…Increased carotid artery blood flow is consistent with the hypothesis that blood flow is redistributed from peripheral circulation to cerebral circulation (Pan et al, 1997). A reduction in skin blood flow during simulated dives in trained breath-hold divers indicates a vasoconstriction in peripheral capillary beds (Andersson et al, 2002).…”

Extreme human breath-hold diving

“…The ensuing increase in peripheral vascular resistance suggests strong peripheral vasoconstriction (Lin et al 1983;Bjertnaes et al 1984). In fact, peripheral blood¯ow is reduced during breath-holding (Sterba and Lundgren 1988;Andersson and Schagatay 1998), but carotid artery blood¯ow is increased (Jiang et al 1994;Pan et al 1997), in agreement with the hypothesis of blood¯ow redistribution towards the brain.…”

“…The basic diving technique has undergone little change, although the introduction of ®ns and the use of wet suits instead of cotton suits have improved diving performance. The speed of descent and ascent has increased, so that the time spent at the bottom has grown to 40% of the diving duration (Park et al 1983a). Both developments are energy-saving, the former by reducing the energy cost of diving, the latter by reducing the thermal stress.…”

The Effects of Hyperbaric Exposure on Immediate and Delayed Changes in Core Temperature and Its Circadian Fluctuations

“…Both the intense vasoconstriction of peripheral and visceral capillary beds and a reduction in oxygen consumption lead to oxygen being spared for use in priority organs, such as the brain or heart [4]. The increased blood flow in the jugular artery is consistent with the interpretation that blood flow is diverted from peripheral to cerebral circulation [5].…”