Reduction of Venous Emboli Load After Breathing Normobaric Oxygen Compared to Air
Condition: Hyperbaric; Diving Medicine; Decompression Sickness; Central Nervous Injury; Inflammation; Endothelial Dysfunction
MeSH terms: Inflammation; Decompression Sickness
Study type: Interventional
Phase: Phase 2/Phase 3

Summary: 
      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
    

Detailed description: 
      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.
    

Intervention name(s): Oxygen; Air
Intervention type(s): Drug; Other
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Triple (Participant, Care Provider, Investigator)
Primary purpose: Prevention