Hi Dr Deco,
Thanks for such a full and informative reply.
>That there are deserved and undeserved hits is a pious fiction. It is a holdover from the classical thought of a fine line separating bends/no bends regions of a dive table.
I said "undeserved" because there was no fast ascent which would have been the most likely trigger.
However, 1hour 40mins after a 31m dive, I had a brief (less than 2 mins - no show on computer)with a Novice who had a problem and then we went to ~11m for 20mins.
>Errors in diving can result in problems even though you are "within the tables" the classical definition of undeserved. Since it is not possible to view you dive day as though it were an instant replay, it is necessary to speak in generalities.
See
http://www.geocities.com/carolreid86/diving_belle1.html
for computer printout and indepth account of the day.
snips.....
>susceptible to DCS (for a given altitude). Why this difference exists is not known, but it is real and it is reproducible. It might well be related to differences in surface tension of the body fluids or differences in biochemical constituents of the fluids (e.g., blood) that accounts for the ease of formation and lifetime of tissue gas micronuclei (the seeds from which decompression bubbles grow). When it comes to formation of bubbles, you might simply be an individual who is bubbles prone."
Would this not have shown up on any of the previous 300 dives?
>[2] If one should
create a large number of tissue micronuclei, these will develop into decompression bubbles.
Nuclei-generating maneuvers might include such activities as climbing ladders onto the boat with full gear, lifting heavy tanks on deck, jumping, running, or other straining maneuvers. These bubbles could pass into the arterial circulation to embolize the brain (past a PFO or through lung capillaries) if there is a rise in pulmonary artery pressure (the large vessel between the heart and the lungs). This is common when an individual performs a Valsalva maneuver. It is also possible with a Valsalva-like maneuvers. Such actions might be straining as you climb the ladder to the boat, pulling or tugging on something, all the while holding your breath for a couple of seconds.
Even if you had only a small PFO, problems could arise. If the CNS DCS that you acquired was
in the spine, a PFO is really not involved in the etiology (= cause).[/list] This is is only the viewpoint from the aspect of decopression biophysics. There are other medical viewpoints that would concern, for example,the validity of the MRI test or how the PFO test was actually performed [e.g., thranthoracic (=chest) echo contrast]. Some are not as sensitive as others.
I was given two tests
the colour contrast echocardiogram first and then, on request, bubble contrast EEG.
But not, significantly, when performing the Valsalva.
>Hope that this will be of some assistance, at least as far as background information is concerned.
Thank you - most of it I have already gleaned from Net sources.
BUT I had not realised that the effort involved after a dive (hard physical exertion) would be so important - this may have caused the second bend 7 weeks later.
In this case, the bends were NOT undeserved.
Does this mean that if I am very careful NOT to have this type of exertion I might be safer?