Dive Medicine
ASD, PFO, Shunts and Diving
BY DR. DAVID SAWATZKY These two photos don’t have anything to do with the
subject but we thought you’d enjoy them all the same
meeting of the senior diving medicine consultants for the military in Canada and after debating this topic for an entire day, we were unable to come to agreement on its significance. The basic problem is that divers frequently develop bubbles in veins
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returning blood from the tissues to the heart after they surface from a dive. These bubbles are normally pumped from the heart to the lungs where they are filtered out and eventually disappear without lasting harm. However, if a right to left sided shunt exists the bubbles can pass through it into the arteries going from the heart to the body, bypassing the lungs. This creates a situation identical to the intra-arterial bubbles in arterial gas embolism after pulmonary barotrauma. Logically, these bubbles should cause serious symptoms and potentially death. There are two other situations where right to left sided shunts are of
concern: strokes and migraines. People often form blood clots in the veins of their legs, particularly after sitting for a prolonged period of time (long airplane flights).
If these clots break free from the walls of the veins, they
can be carried from the legs to the heart and are normally filtered out in the lungs, just like bubbles. A very large clot or multiple smaller clots can block so much of the blood flow to the lungs that the person develops serious or
Magazine
he topic of right to left sided shunts has been a matter of major concern and discussion for many years in diving medicine. I first wrote on this topic in DIVER in 1999 and updated the discussion in 2006. Since then data gathering has continued but the topic is just as controversial now as ever. Earlier this year I attended a
fatal problems (pulmonary embolism). However, small clots are usually asymptomatic and resolve without significant damage. If a right to left sided shunt exists, clots can pass through the shunt and then down the arteries to the brain/body. Some types of strokes, some types of migraines,
and some types of decompression sickness seem to be associated with right to left sided shunts where venous clots or bubbles bypass the lungs and enter the arteries to the brain. There are three kinds of right to left sided shunts:
atrial septal defect (ASD), patent foramen ovale (PFO) and transpulmonary shunts. Transpulmonary shunts are relatively rare.
Cardiac Cycles The human heart has four chambers but it is really two pumps that have two chambers each, pumping side by side. Blood is collected from the tissues by the veins and returned to the right side of the heart (right atrium). From the right atrium blood moves into the right ventricle and is pumped from the heart to the lungs. Blood is collected from the lungs by the pulmonary veins and returned to the left side of the heart (left
Photos:
davidfleetham.com
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