Bubble Formation and Endothelial Function Before and After Three Months of Dive Training

Bubble Formation and Endothelial Function Before and After Three Months of Dive Training

Poor decompression following diving leads to bubble formation in tissues and blood vessels which causes decompression sickness (DCS). Bubbles have been clearly shown to be the root cause of DCS, but often these “silent bubbles” go undetected. It has been shown that repeated diving exposures decrease the susceptibility to bubble formation. A single bout of physical activity prior to a dive has been shown to decrease detection of bubbles via Doppler system. It is possible that the endothelial function of the individual has improved with repeated diving therefore releasing a greater amount of Nitric Oxide (NO). Since a single dive inflames the endothelium, it is possible that dive training will adapt the endothelium and increase NO production. The aim of this research was to see if dive training will decrease bubble formation and enhance endothelial function.

Twenty-two healthy men (25.3±0.8 yrs) who were all recreation divers (46±3 dives in the last 5 years) participated in this study. These men were part of a military diving course in which the first three months did not include diving, the next three months included dives to increasing depths and physical exercise (60 min of running) and the last three months included strictly physical exercise. Subjects maximal oxygen uptake was assessed via cycle ergometer pre and post dive training.

One week prior, one week post and three months post dive training subjects were decompressed in a dry chamber to ~30 msw for 30 minutes. The subjects were slowly decompressed to normal atmospheric pressure to avoid sickness. After decompression, bubble formation was detected using a pulsed Doppler measured at the level of the precordial area every half hour for ninety minutes. The formation of bubbles were graded and plugged into the KISS equation to measure the activity of bubble post-decompression.

Endothelial function was assessed one week prior and one week after the training period using Doppler flowometry. Endothelial function was assessed on the ventral side of the non-dominant forearm no longer than forty-eight hours after the last training session. Cutaneous blood flow was measured when the subject was at rest which was used as a baseline measure, after a blood pressure cuff occluded the upper arm for three minutes at 200 mmHg and when the area of the transducer was warmed to forty-two degrees celcius. The aim of the occlusion and local heating was to assess how well the endothelium responded to these stimuli by way of NO.

On average the subjects weight, BMI or cardiovascular fitness did not change throughout the course of the study. KISS bubble score decreased significantly from pre to post training, but significantly increased from post training to 3 months post training. The cutaneous vascular conductance (CVC), or endothelial function did not change from pre to post across all the stimuli.

The researchers successfully eliminated any outside artifact by have the divers be compressed and decompressed in a dry chamber to simulate underwater pressure. This was very important to the reliability of the study because all subjects experienced the exact same conditions. The results of this study are pretty mundane and are typical of a training study. With regular physical exercise and repeated dives, these divers experienced less bubble formation in their post measures. Also, when the divers detrained their bubble formation increased yet again. The researchers speculated that the release of NO from the endothelium may be the mechanism that aids in the reduction of bubble formation, but this was found to be untrue. The mechanism behind bubble formation is still unknown, but studies showing that enhanced cardiovascular fitness leads to less bubble formation. The authors suggest that heat shock proteins that are induced during endurance exercise may have protective effects against embolisms. These divers did partake in endurance exercise the mornings of their dives, but how long does this protein stay in circulation and have an effect on the bubble formation.