Differential influence of vitamin C on the peripheral and cerebral circulation after diving and exposure to hyperoxia

Abstract

We examined if the diving-induced vascular changes in the peripheral and cerebral circulation could be prevented by oral antioxidant supplementation. Fourteen divers performed a single scuba dive to eighteen meter sea water for 47 min. Twelve of the divers participated in a follow-up study involving breathing 60% of oxygen at ambient pressure for 47 min. Before both studies, participants ingested vitamin C (2 g/day) or a placebo capsule for 6 days. After a 2-wk washout, the study was repeated with the different condition. Endothelium-dependent vasodilator function of the brachial artery was assessed pre- and postintervention using the flow-mediated dilation (FMD) technique. Transcranial Doppler ultrasound was used to measure intracranial blood velocities pre- and 90 min postintervention. FMD was reduced by ~32.8% and ~21.2% postdive in the placebo and vitamin C trial and posthyperoxic condition in the placebo trial by ~28.2% (P < 0.05). This reduction in FMD was attenuated by ~10% following vitamin C supplementation in the hyperoxic study (P > 0.05). Elevations in intracranial blood velocities 30 min after surfacing from diving were reduced in the vitamin C study compared with the placebo trial (P < 0.05). O2 breathing had no postintervention effects on intracranial velocities (P > 0.05). Prophylactic ingestion of vitamin C effectively abrogated peripheral vascular dysfunction following exposure to 60% O2 but did not abolish the postdive decrease in FMD. Transient elevations of intracranial velocities postdive were reduced by vitamin C. These findings highlight the differential influence of vitamin C on peripheral and cerebral circulations following scuba diving, which are only partly mediated via hyperoxia.