Was his death due to immersion pulmonary oedema rather than drowning as recorded by coroner?
First off Hey Jude, sorry for your loss. I realize time does little to diminish the pain.
In case you don't know, I work as a forensic consultant for the LA County Coroner for scuba fatalties. Understand that protocols may vary from jurisdiction to jurisdiction but based on the way things are don here, it's not uncommon for the cirumstances you describe to result in a cause of death (COD) that's drowning.
Remember that the coroner's job is to determine COD with reasonable medical certainty. And when we're talking COD, it means the mechanics of death, not necessarily what caused the mechanics to occur in the first place (which DAN refers to as the "trigger"). Also, drowning is a diagnosis of exclusion. In other words, you can "prove" that someone drowned. You can have "dry" drowning and you can have "wet" drowning, so water in the lungs in and of itself or the absence of that is not necessarily indicative. But what you can do is take the fact that someone was found underwater, rule out things like heart attack, head trauma, etc., and eventually all you're left with is drowning.
Here's what DAN says about it: "Pulmonary edema is an abnormal leakage of fluid from the bloodstream into the alveoli, the microscopic air sacs in the lungs. It is most often the result of heart failure or other cardiac problems. Sometimes, however, pulmonary edema is observed in swimmers and divers when no underlying medical cause is apparent. This condition, immersion pulmonary edema (IPE), presents as a rapid onset of shortness of breath, cough and sometimes blood-tinged, frothy sputum. Because the fluid builds up in the air-containing spaces of the lungs and interrupts gas exchange, IPE resembles drowning. The important difference is that the obstructing fluid comes from within the body rather than from inhalation of surrounding water."
In the case of your brother, just from what you've described, it could be that immersion pulmonary edma (IPE) started everything going wrong. He then possibly could have embolised, which given the depth, his lack of recent dives, likely problem of breathing with IPE, all could have contributed to a rapid, breath-holding ascent which at that shallow depth easily could produce an embolsim. But no matter how it started, then end result in terms of COD still could be drowning. It could also be that, as the DAN statement points out, that he "drowned" in his own fluids.
Because he was alone, you don't really know if he was upright or not, you don't know if he coughed underwater (the police comment is simply speculation), you don't know if he kicked hard, and you don't know when he realized he was in trouble because none of these things were observed by anyone. It may all be correct but there's no way to know for sure.
If foul play was not suspected by the coroner (which I assume it wasn't) and given everything else you've stated, at some point the politics of the situatoon are such that the coroner would like to close the case and probably felt there was little real difference between drowning and IPE. And if they don't deal with diving deaths very often, it's certainly possible they could have missed the IPE and just gone with drowning. Absent a re-test of the fluids collected from the lungs, I'm not sure there's any way at this point to know for sure.
Hope this helps and for any of the medicos here, feel free to correct or expand on anything I haven't gotten 100% correct.
- Ken