swamp diver
Contributor
Also remember that CO is eliminated by the lungs at a rate dependent on the partial pressure of oxygen. If a diver has a smoke on the shore and loads his blood with 9 percent COHb then five hours later his blood concentration will be 4.5 percent assuming he doesn't have another smoke.
If however he puts on a mask delivering 100 percent oxygen a concentration of 4.5 percent COHb will be reached in only 60 to 90 minutes. Throw him in the chamber and that elimination half life can be reduced further.
So in effect once the rebreather is strapped on with a set point say of 1.0 the diver is driving more CO off the hemoglobin and back into the loop such that the affinity is no longer 200:1 as it was on the surface.
As Laura mentioned one can tolerate a higher COHb underwater because oxygen is dissolved into the blood plasma which compensates for the lost carrying capacity due to CO bound to the four O2 binding sites on the hemoglobin molecule.
I recall that on one of the CO fatality/injury threads a while back a board member who is an anesthesiologist showed that even at deep recreational depths and with a high COHb concentration which might be fatal on the surface there would be enough dissolved oxygen in the plasma alone to sustain brain and bodily functions if resting.
The problem is that upon surfacing the partial pressure of oxygen drops lowering the dissolved oxygen plasma concentration however the CO molecule still remains bound to the hemoglobin preventing O2 transport to the tissues. The diver may have been functioning ok at depth but with the loss of plasma O2 he may lose consciousness upon surfacing if the COHb concentration has become high enough over the dive.
The Maldives CO incident was a classic case of this with the divers ok until they surfaced at which time mulitiple divers lost consciousness and one died. There were many divers who said they were fine at 80 feet but as soon as they hit approximately 30 feet they experienced the sudden onset of anxiety and shortness of breath which only worsened further as they surfaced and the dissolved plasma oxygen concentration fell to ambient air concentrations. Some recovered consciousness on ambient air alone as the oxygen system on the boat was not working but one unfortunate diver expired.
He likely had a higher concentration of CO in his tank, may have traveled to a greater depth, or may have had a higher level of exertion all of which would increase his COHb concentration further over the duration of the dive.
http://coheadquarters.com/coremove1.htm
http://coheadquarters.com/figco06.htm
to DAN.
I do hope they have a bigger plan in mind.
