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  • AutorenbildMichael Mutter

The most important dive paper 2023

... or the last few years was already discussed in this blog before publication. Dekoblog has got the details.


Image template: Karin Aggeler

Venous gas emboli (VGE) are often used as surrogate markers (substitute endpoints) for decompression sickness (DCS) in studies of decompression procedures. Peak VGE values after repeated identical dives vary widely, but little is known about how much variability there is in VGE values between different divers and in the same diver.


Methods

Doolette analyzed 834 dives from a register of the NEDU (Navy experimental diving unit) with six dive profiles, which were carried out under controlled laboratory conditions. Ultrasound VGE measurements were taken after each dive. This data included 151 divers who dived the same profile repeatedly on two to nine occasions at least one week apart (693 dives in total). The data were analyzed for post-dive variability in peak VGE values.


Results

After repeated dives with the same (!) dive profile, most divers showed a wide range of VGE values with a very large spread (Figure 1). If no or only very few VGE could be detected on one day, a very high number of VGE occurred after an identical dive with the same diver on another day and vice versa. There was only a very weak correlation between the extent of VGE and the occurrence of DCS.


Screenshot: rebreather forum 4. David Doolette, Advances In Decompression Theory And Practice

Figure 1: Occurrence of bubbles in an individual diver. Each vertical line represents multiple, identical dives by the same diver. Each dot shows the extent of VGE after the dive (VGE grade: 0=no bubbles, 4=massive bubble formation). Red dots=DCS. On the left rather short, shallow dives; on the right rather deep, long dives (compressed air). The variability is very large. There is almost no DCS.


Conclusion

The results are so important because they are striking due to their very wide intra-individual range of variation and because no previous comparable data was available. Apparently, one day a diver tends to have a high number of venous gas bubbles, another day a low number. The good news is that the risk of DCS is low even with many VGE. However, if a DCS occurs, it occurs with many bubbles. For this reason, it is important to act in such a way that only a few bubbles occur.


Big question marks over individual susceptibility.

In addition to the ongoing search for strategies to minimize bubble formation after a dive, it is particularly important for research to identify and, if possible, influence the as yet unknown factors that are responsible for the large variability in VGE.

The reasons for the variability are certainly complex. Most gas bubbles are filtered out in the pulmonary capillaries, which partly explains the discrepancy between VGE and DCS. As Doolette explained at the rebreather forum 4, IPAVA (intrapulmonary arteriovenous shunts) may also be involved in this variance. However, it is still poorly understood under what circumstances they shunt gas bubbles past the lungs directly into the arterial circulation.

"For an individual, measuring VGE ist not a useful tool."- David Doolette, Rebreather Forum 4

Questionable benefit for self-detection of VGE

In any case, these results cast considerable doubt on the usefulness of commercially available tools for detecting bubbles (e.g. O-Dive). However, it should be noted that individuals should question their diving strategy if they always detect a high VGE load after dives.

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