The 2017 European Underwater and Baromedical Society’s (EUBS) conference left us with more questions than answers on the topic of postdive bubbles.
Ballestra presented the preliminary results of an exploratory study of the effects of sonic vibrations on post-dive venous gas emboli (VGE) detected by transthoracic echocardiography.1 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 or something 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 decompression sickness (DCS) cases in aircraft pilots.
In another study, the presenting author used contrast echocardiography, a standard clinical method, to monitor divers post-dive.2 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 classic 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.
- Ballestra C., et al. Can sonic vibrations increase the number of decompression vascular gas emboli? P 12.
- Papadopoulou V., et al. Can current contrast mode echocardiography help estimate bubble population dynamics post-dive? P 18.
- Genser M., et al. Incidence of lost-dive bubbles and DCS using the US Navy Revision 6 air tables. P 34.