Reduction of Venous Emboli Load After Breathing Normobaric Oxygen Compared to Air

Central Nervous Injury, Decompression Sickness, Diving Medicine, Endothelial Dysfunction, Hyperbaric, Inflammation

Primary objective: \- Assessment of venous gas emboli load post diving when breathing normobaric oxygen compared to air. Secondary objective: * Assessment of fluid markers of central nervous system injury in blood post diving * Assessment of fluid markers of inflammation and endothelial dysfunction in blood post diving Tertiary objective: \- Assessment of DCS frequency

This is a prospective, double blinded, randomized, cross-over study in Sweden. The study was performed in two different sets, each containing standardized dives in a wet hyperbaric chamber. The dives included movement on depth. In each study set 16-32 professional divers performed no-decompression dives to a depth of 42 metres of seawater (msw). The gas used during the dives was compressed air. After surfacing the divers breathed either normobaric oxygen or normobaric air on a demand mask. Timing of oxygen/air-breathing differed between study sets. The content of breathing gas was unknown to both divers and examining personnel. Immediately post dive the divers were assessed using either transthoracic doppler ultrasound (TTD) or transthoracic 2-D ultrasound (TTE) to determine VGE load, time to VGE detection and VGE duration. Signs of DCS were actively sought. TTD measurements were done every five minutes during the first 30 minutes, thereafter every 15 minutes during 90 minutes. TTE was performed every 30 minutes, using an apical 4-chamber view. Blood samples were obtained pre-dive, 30-45 minutes post-dive and 120 minutes post-dive. Set 1: 16 divers, divided into two equal groups (A and B). Dive to 42 msw during 10 min with a safety stop at five msw during three min. Immediately post dive breathing of oxygen (group A) or air (group B) during 30 min. VGE load, time to VGE detection and VGE duration is recorded. Blood samples were obtained pre-dive and 30 and 120 minutes post-dive. After 48 hours, the dives were repeated with switched gases between the groups. Set 2: 32 divers, divided into two equal groups (A and B). Dive to 42 msw during 10 min with a safety stop at five msw during three min. Fifteen minutes post dive breathing of oxygen (group A) or air (group B) during 30 min. VGE load, time to VGE detection and VGE duration is recorded. Blood samples were obtained pre-dive and 45 and 120 minutes post-dive, from the first 16 divers. After 48 hours, the dives were repeated with switched gases between the groups. Two further planned sets with repeated diving and shorter duration of oxygen/air-breathing were never carried through. AE including SAE will be recorded during the study. DCS may be considered either an AE or SAE depending on severity. Ongoing AE and SAE will be followed up.

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