Venous gas emboli

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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What’s Left to Learn about Bubbles?

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EUBS 2017 has left us with more questions than answers, on the topic of post-dive bubbles.

Ballestra presented the preliminary results of an exploratory study of the effects of sonic vibrations on post-dive venous gas emboli detected by transthoracic echocardiography1. Six divers performed dives to a depth of 33 meters depth for 20 minutes, in a fresh, warm water pool. Bubbles were detected in a standard way, with and without exposure to a sonic vibrations of 20 to 30 Hz. The amount of detected bubbles nearly doubled after sonic vibrations. If these preliminary result get confirmed, we will have to be concerned with post-dive exposure to a sonic noise from various sources, like music, helicopter vibrations and similar, and it is possible that we could find some convenient and fun ways to pre-condition our bodies before dives. This should be also considered in DCS cases in aircraft pilots.

In another study, the presenting author used contrast echocardiography, a standard clinical method, to monitor divers post-dive2. Unlike the more commonly used B-mode echocardiography,  which can detect circulating bubbles greater than 35 microns, the contrast echocardiography can detect much smaller bubbles (< 10 microns). Post-dive contrast echocardiography in seven divers did indeed show the presence of small bubbles in the right and left heart, even in absence of large bubbles detectable by standard B-mode echocardiography. Of particular note is the fact that the presence of small bubbles did not correlate with the amount of large bubbles detected.

The final study was a classical bubble study done by scientists from the Swedish Navy to evaluate the safety of the US Navy Diving Manual Revision 6 air decompression tables. Twenty-eight divers did 72 dives in controlled conditions with three different dive profiles at the no-D limit, or with one required decompression stop. Most dives resulted with VGE Spencer grade III or higher. Two divers were treated for limb DCS and four divers with high bubble load were given surface oxygen. This study confirms that high VGE grade correlates with the risk of DCS.

While the value of VGE monitoring for evaluation of decompression safety at the population level is not questionable, it does have clear limitations that are primarily reflected in great inter- and intra-individual variability. New technologies may help us to learn more about post-decompression bubbles dynamics and get closer to the personalized approach in prevention of DCS.

 

  1. Ballestra C., et al. Can sonic vibrations increase the number of decompression vascular gas emboli? P 12.
  2. Papadopoulou V., et al. Can current contrast mode echocardiography help estimate bubble opulation dynamics post-dive? P 18.
  3. Genser M., et al. Incdence of ost-dive bubbles and DCS usingthe US Navy Revison 6 ait tables. P 34

 

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.

Can a Test Identify Divers Who May Be More Susceptible to DCS?

Are some divers prone — or resistant — to gas bubbles after diving?

Decompression sickness (DCS), which may occur in divers after decompression from a dive, is dependent on the combined dose of gas saturation during the dive and the rate and magnitude of decompression. However, there is a great variability of outcomes in subjects exposed to the same dive profiles. The variability decreases as the severity of exposure increases.

DCS is correlated with the degree of venous gas emboli (VGE), or “bubbles”, in circulation after a dive. Generally, the higher the VGE grade (more bubbles) the greater the probability of DCS, and vice versa. Similar to DCS, there is a great variance in the probability of VGE appearing postdive. Some researchers who practice VGE detection have hinted that some divers bubble after most dives and may exhibit a high bubble grade (HBG) and others tend not to bubble at all or rarely exhibit HBG. The former are often labeled as bubblers (or high bubblers), while the latter are labeled as nonbubblers (or low bubblers).

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