Dave, great thread.
Bubbles moving from venous circulation by shunt (ex. PFO or pulmonary) or transpulmonary passage another mechanism to add to your list.
Individual pathophysiology could also come into play. Are the lungs healthy? Many people have blebs they are not aware of and the blebs could cause gas trapping. Is the diver sick (wheezing)? Fluids in the lung could also cause gas trapping.
This is an interesting question but it begs two more, why was the diver unconscious? and/ or how long was the diver in laryngospasm? Hypoxia will actually cause a laryngospasm to relax and the gas to escape.
Barotrauma and brain infarcts are easily viewable on autopsy. There are procedures that should be taken with diving fatalities that not all pathologists are aware of the differences so greater access and support should allow for better reporting. For more on diving autopsies, download the Caruso from our suggested reading list on
diving fatalities. (WARNING: Jim's talk is very graphic as it was intended for Pathologists.)
Gene, I can't thank you enough for your input and for steering me to Rubicon's extensive compilation of articles on this subject and many others!
(I've gratefully sent a donation to help fund Rubicon's FREE service of compiling and providing these invaluable articles. What a treasure!)
Dr. Caruso's presentation was fascinating.... actually mesmerizing! Your warning about the graphic quality is well-advised for those not accustomed to objective science. Aside from the details of the physiology, the overview of diving accidents and the methodology to determine cause of death was captivating.
I've just finished reading two other articles in this area of Rubicon's vast collection, including one case of AGE occuring in a healthy diver who was repeatedly dunked from the surface down to 10' and back while holding onto a buoy in rough seas. It illustrated how little it takes to overpressurize full lungs and how even simple mistakes or misfortune can quickly turn into disaster. The discussion of autopsy techniques and rationales was helpful.
Regarding my question, numerous scenarios can be imagined how an otherwise healthy, skilled diver might sense he's in trouble and begin an ascent before blacking out, say from a hypoxic mix or from a seizure related to oxygen toxicity. I assume aspiration would soon follow, resulting in laryngospasm and finally barotrauma under some conditions if the laryngospasm lasted long enough for overpressurization of the lungs to occur.
I'll take a look through Rubicon's archives regarding how long it might take for hypoxia to relax a laryngospasm. If it takes as long as a couple minutes, that might be long enough for an ascending diver's lungs to overpressurize. Unfortunately, the other scenario is that the laryngospasm relaxes and he simply drowns.
I've a great deal of respect for the risks inherent in diving and how easily one can lose consciousness for any number of reasons, even as simple as hyperventilation or a small aspiration of water during a mis-timed regulator switch.
If one is alone and the regulator falls out of the mouth, the end is certain. With a buddy, perhaps the regulator could be replaced in the mouth and maintained there as the diver regains consciousness, but it's hard to imagine handling the panic reaction of the stricken diver as he awakens in a coughing fit underwater with someone manipulating his head and mouth.... I wonder if such a rescue has ever been successful.
Anyway, I'm in danger of becoming a summer recluse reading Rubicon's informative articles!
Kindest regards, and again, many thanks for tremendous resource!
Dave C
