Breath-hold diving

Venous gas bubbles in breath hold divers

Venous gas bubbles in breath hold divers remained a focus of researchers this year, with a notable presentation coming from Danilo Cialoni and his EDAN team1.  At EUBS 2017 they presented the extension of study previously reported and described in this blog. After discovering post-dive VGE in one breath hold diver, they studied VGE in 37 elite breath hold divers during their training in 42 meter deep pool with water temperature  of 32 oC.

Divers underwent echocardiographic Going downmonitoring before the series of dives, after a number of training dives, and every 15 minutes for up to 90 minutes after the last dive. Bubbles were detected in 39% of divers (28% low VGE grade and 11%  high VGE grade). Bubblers did significantly longer and deeper dives with shorter surface intervals. The data from this study will be used to correct the decompression algorithms for breath hold divers, which primarily means extending the time between the dives to prevent carrying over dissolved gas from one dive to another. Four divers did develop neurological symptoms of taravana during the study. All symptoms were mild and divers recovered after breathing oxygen at surface. Most notably, in one diver with taravana, bubbles were not discovered.

Another taravana case unrelated to this study was presented by another group2. A 39 year old diver performed about 30 dives over the course of 5 hours to depths between 29 and 32 meters, with dive times between 2 and 2.5 minutes each. A few minutes after his last dive the individual developed expressive aphasia (difficulty speaking and expressing thoughts) and a headache. The aphasia resolved shortly but the headache persisted and diver was admitted to an emergency department 48 hours post dive. The diagnostic workup included the brain MRI which revealed a brain injury. The patient was treated with one Table 6 and five HBO treatments at 2.5 ATA on the following days. His conditions significantly improved after the treatment and at 2 months follow up he was completely recovered.

Competitive breath hold divers should be aware that post-dive symptoms may be caused by brain injury and regardless of assumed cause (decompression or hypoxic) they need neurological examination and treatment in case of confirmed injury.

 

Sources:
  1. Cialoni,D. et al. Prevalence of venous gas emboli in repetitive breath hold diving. Proposal for a new decompression algorithm. P 17
  2. Guerreiro F, et al. Decompression illness in extreme breath hold dive (Taravana syndrome) – A case report. P 47
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BREATH-HOLD DIVING, CIRCULATING GAS BUBBLES, AND NEUROLOGICAL SYMPTOMS

Decompression sickness has been the suspected cause of the post-dive symptoms of brain injury in breath-hold divers for a long time, and the quest for the proof of culprit has been ongoing, but without success. In the meantime, many possible explanations of neurological symptoms in breath-hold divers were proposed, including in-situ bubble development, lung barotrauma and consequent gas embolization, atherosclerosis, small vessel disease, transitory extreme elevation of blood pressure, and repeated hypoxic injury.

Several researchers have studied venous gas emboli in breath-hold divers, but their results have been mixed. Spencer reported in 1972 positive finding of VGE in Ama divers of Japan after repetitive breath-hold diving. Lamaitre reported in 2009 finding of the lowest freediver-istock_webVGE grade in one out of twelve Ama divers.  On the other hand, Boussuges could not find any bubbles in ten divers diving repeatedly for two to six hours up to 34 meter depth. More details on those studies can be found in another post on this blog, in which I admit that clinical documentation of decompression sickness-like symptoms and signs appears supportive of a DCS diagnosis. The bulk of material presented by the researchers was, however, more circumstantial than crucial evidence.

Recently Cialoni and co-authors (1) published in UHMS a report about finding high grade bubbles in breath-hold divers lasting for 45 minutes post dive and declining over the following 90 minutes. This diver did not have any symptoms, but the bullets were flying around and there was a potential for arterialization of bubbles and, if the diver had a PFO, embolization of the brain. This outstanding finding, they explain, is a result of 14 deep dives (40 m) and long bottom times (141+-42 seconds), typical for advance spearfishing divers.

However, another outstanding circumstance is that these dives were conducted in warm water (33 0C; 91.4 0F), which was uniform throughout the water column, which is higher than usual water temperature where the spearfishing occur. It was shown previously that diving in warm water increases the bubble grade three-fold (2), and may increase an individual’s risk of DCS.

Regardless of the circumstances, the finding of Cialoni and coauthors is the proof of hypothesis that breath-hold diving may generate venous gas bubbles. The true relationship of VGE and post-dive neurological symptoms is not known. The VGE may not be necessary for cerebral decompression sickness. Finally, the DCS may not be the only cause of cerebral symptoms occurring after deep and repeated breath-hold dives. More investigation on the topic is necessary, and some studies are ongoing and we hope that more results will come soon.

References:

  1. Cialoni D., et al. Detection of venous gas emboli after repetitive breath-hold dives: case report. Undersea Hyperb Med 2016;43(4):449-455
  2. Dunford R. Hayward J. Venous gas bubble production following cold stress during a no-decompression dive. Undersea Biomed Res, 1981;8(1):41-49.
  3. Gerth WA. On diver thermal status and susceptibility to decompression sickness. Diving Hyperb Med. 2015 Sep;45(3):208.