Originally Posted by
double_barrel
Cold you point me to some background on that? My understanding is that, as you say, CO binds very tightly to Hb blocking O2 attachment, but I wasn't aware of any detectable damage to the rbc's themselves. And even if that was the case, I would expect virtually every rbc to be lysed so long post mortem. I had assumed that CO would eventually dissociate from Hb after death because of all the changes that must completely screw-up the Hb molecule. i guess maybe some blood deep in the tissues would be preserved well enough for an analysis?
I was probably a little careless in my choice or words - in this instance by "damaged" I meant that the Hb is permanently put in a state where it cannot transport oxygen - once it has formed CO-Hb i6t is essentially impossible to get it to release the CO and form the O2-Hb which can accept and release oxygen in the "usual" manner, so (in my usage) the Hb is "damaged". There are various ways of determining the propotion of CO-Hb in a blood sample (and indeed in other body fluids) from gas chromatography at the expensive/accurate end to manual spectrometry at the "cheap, time-consuming and reliant on skill" end. But most path labs use an autmated spectrophotometry technique, usually in the form of a specifically designed "CO-oximetry analyser". These machines have proven to be pretty reliable and sufficiently accurate to give a confident post-mortem indication of whether CO-Hb was a cause (or significant contributor) of death.
CO-Hb itself seems to be a remarkably robust and stable molecule which doesn't decay much in normal conditions, and barely decays at all when chilled, so a few days on the sea bed is unlikely to compromise the results significantly. There was a reason why I was aware of all this which I'm afraid I can't go into, but the subject of post-mortem determination of C) poisoning is a well published field because (I understand) CO-poisoning is the most common form of lethal poisoning in the western world. Most of the papers get very technical very quickly, but an easily digestable source would be this one:
https://acutecaretesting.org/en/arti...em-co-oximetry
You may be espcially interested in the section headed "STABILITY OF COHb WHEN MEASURED BY CO-OXIMETRY" (about 2/3ds of the way down) which provides the following:
"A number of studies [23, 27, 28] have addressed the issue of stability of COHb as measured by CO-oximetry in stored blood samples. They have confirmed that COHb is remarkably stable.
No change in CO-oximetrically determined COHb from baseline was noted in postmortem samples collected into heparin and stored for up to 3 years in a refrigerator [28].
Hampson [27] determined that there was no significant change from baseline in COHb for unrefrigerated samples mailed across the US and back again. And Kunsman et al[23] confirmed that stability of CO-oximetrically determined COHb was not dependant on the use of a particular anticoagulant/preservative combination."
HTH,
PDR