DAN Showcases Advances in Using Ultrasound in Dive Safety Research

It’s a boy! Well, not really. The Divers Alert Network sponsored a seminar here at the DEMA Show on the latest advances in the use of ultrasound for dive safety research. Dr. Neal Pollock, director for hyperbaric and environmental physiology at the Duke Medical Center in North Carolina, talked about trans-thoracic echocardiography, where one can take a portable monitoring unit either onto a boat after a dive or into a hyperbaric chamber and see whether the heart is pumping any nitrogen bubbles after a dive. If the bubbles are on the right side of the heart, that’s fine because they then go into the lungs which can handle them. If the bubbles are on the left side of the heart, that can be a problem, because the bubbles would then go into the body and lodge somewhere, causing the bends.

The future of ultrasonic monitoring, according to Pollock, is in dual-frequency ultrasound, where

two transducers are used – one a pump transducer that excites the bubbles and the other an image transducer that enables the viewer to identify when a bubble starts vibrating. Also, the system doesn’t rely on doppler-shift-type ultrasound when monitoring bubbles moving through the bloodstream. The new technology alows the measurement of stationary bubbles.

“If you think about it, all of our data to date are based on bubbles in the bloodstream, we know nothing about bubbles in the extravascular tissues where in fact it may be more important,” he said. “So, dual-frequency will allow us to look at extravascular bubbles. Also, because of that frequency sweep potential, it will also allow us to size bubbles, which will allow us to compute gas volume.”

This technology was proposed 25 years ago and has taken until now to start overcoming the technical challenges of trying to measure bubbles with a dual-frequency system, according to Pollock.

But Pollock emphasized that merely having those gas bubbles in the bloodstream do not necessarily mean someone is suffering from decompression sickness, and that data from ultrasonic equipment should be measured conservatively.

It’s even more difficult to look for bubbles in freedivers, Pollock said, because it requires getting to the freediver immediately after a dive to see if he or she has any nitrogen bubbles. Not only that, while he had heard of anecdotal accounts of freedivers exhibiting bends symptoms, Pollock said it may not necessarily be nitrogen gas – it could be oxygen toxicity. — John Liang