Exploring Decompression Bubbles Using Advanced Ultrasound Techniques

Venous gas emboli (VGE) are bubbles that can appear in the blood after a dive due to decompression. These bubbles are detectable using ultrasound imaging and provide a measure of decompression stress. However, how and where VGE form is still not fully understood. There are also unexplained differences in VGE size and quantity and decompression sickness (DCS) risk among and within individuals. Microbubbles are hypothesized to be precursors to VGE, and the ability to detect and measure these microbubbles can provide a new tool in studying decompression physiology and DCS risk. Advanced ultrasound imaging techniques are being developed at the University of North Carolina (UNC) for detecting these microbubbles and differentiating them from VGE.

Bubbles known as venous gas emboli (VGE) can appear in the venous circulation during ascent due to the offgassing of nitrogen from the tissues. Normally the lungs are able to effectively filter them from the bloodstream. Bubbles are commonly measured in diving research using ultrasound imaging of the heart, where they can be seen circulating in the venous heart chambers. Although there is a correlation between bubble load and DCS risk, VGE do not provide a direct measure of DCS.

VGE are hypothesized to grow from tiny microbubbles (smaller than a red blood cell) that are naturally present in the body. Several studies have shown using ultrasound that these microbubbles are produced during diving and after exercise. In medical ultrasound imaging, engineered microbubbles are commonly used as a vascular contrast agent (these are injected in the bloodstream). Advanced ultrasound imaging techniques have been developed to image these microbubbles specifically. Using these ultrasound imaging techniques, it has been shown that ultrasound signals increase post-dive and have different dynamics to VGE detected with normal ultrasound imaging.

At UNC, researchers are repurposing these imaging techniques to selectively detect decompression microbubbles using state-of-the-art ultrasound scanners. Furthermore, they are working on bringing this technology from the lab bench to the field where divers can be studied.

This study is a collaborative effort between the University of North Carolina, Chapel Hill and DAN, and was initiated with funding through the DAN/R.W. Hamilton Dive Medicine Research Grantin 2017.