Dr Deco:
Hello Saturation:
Intrapulmonary Shunts
I have seen these papers before, and the results at first seemed contradictory. The measurement of the intrapulmonary shunts [Strickland et al. paper] was performed with saline contrast that produces very small gas bubbles. These might be expected to have the needed [calculated] lifetime and pass through the shunts of the diameter hypothesized.
We also have a similar experiment performed by Eldridge et al. This did not have the accompanying blood gas measurements.
Dive Bubbles
I do not have the full paper and thus must view what appears in the abstract [Dujic et al. paper]. It is not clear from the abstract exactly when the exercise (to provoke pulmonary arterial pressure increases) was made post dive and the time of the echo measurements. [It might even appear that the echoes were not performed during the exercise.]
I suspect that the difference lies in the diameter of the bubbles. Diving does not generally generate small bubbles in the micro range. Thus, one might guess that intrapulmonary shunts would be of too small a diameter.
There are cases where strange Doppler precordial sounds are detected post dive. I have always surmised that these rare insistences [with a very pronounced flow sound] occur when very small bubbles are generated; one cannot hear any distinct bubble sounds. It is just possible that these cases might produced DCS with exercise (or strenuous activity).
Thanks Dr. D:
The bolded issue is of concern to me in regards to technical diving and particularly CAGE. DCS is less a concern.
There have a been on record a couple of unexplained sudden deaths or loss of consciousness, deaths at times attributed to 'heart attacks', but it happens almost universally to folks within an hour of a dive
and doing strenuous activity, typically carrying 125-150#, if not more, worth of tanks up 3 flights of stairs or atop a ladder on a boat. Such activity is common place in boat and cave diving and most tech divers do so without issue. However, when the uncommon occurs, its striking because its so sudden and without warning, very emboli like.
One such death recently happened and suddenly to a well trained tech diver and documented on The Deco Stop, and there are 2 other cases within the last 6 weeks but the documentation remains spotty.
Assuming bubbles begin as micronuclei, these smaller bubbles are far above what bubble models term the LaPlace radius, and thus grow easier and faster than micronuclei. The 1st hour is the most critical time for offgassing, and here is an opportunity for a bubble to grow, in the wrong place. Had it not been in the arterial side, bubbles of such size would not cause much issue once the offgassing continued over time, and thus the inevitable shrinkage of the bubble.
http://www.springerlink.com/(t4pm2u55vzi15q553r3w032u)/app/home/contribution.asp?referrer=parent&backto=issue,5,38;journal,67,130;linkingpublicationresults,1:102334,1
