IndAeMed_F: Re: Postmortem lividity
- From: SS Mishra <ssmhialt@xxxxxxxx>
- To: indaemed@xxxxxxxxxxxxx
- Date: Fri, 02 Apr 2004 22:14:23 +0530
To my mind, there is no doubt that what Dilish has described is typical post
mortem lividity, as has been excellently discussed by Bish sir,. The reference
quoted by him gives a detailed discussion of the process. The time course, the
location and the type of death, all fit in very nicely. What Arvind has
mentioned is a part of the same process. Indeed, the oxygen continues to leave
Haemoglobin even after death, as cells are not dead for quite sometime after
bodily death, and as long as some oxygen is available, keep extracting it from
hemoglobin, thereby desaturating it. Calling it paying the Oxygen debt may be
slightly fanciful, as the term is mostly reserved for post exercise recovery,
but in essence is not substantially different. The distinction probably is
more semantic than real (as in the case of lividity Vs. cyanosis). There is one
difference between cyanosis and lividity though : in cyanosis, the reduced
haemoglobin remains almost exclusively intravascular, while in lividity, due to
permeability changes in capillaries, red cells leak out in extravascular space.
After some period of hypoxia, the RBC membrane cannot maintain its integrity
and so hemolysis takes place with free hemoglobin escaping into tissue spaces.
This hemoglobin sometimes reacts with gases being formed during early
putrefactive process (eg. sulphur dioxide and methane) and may form darker
colored sulphmethhemoglobin etc., which may impart characteristic dark
coloration to skin, nail bed etc.
Now comes the question of explosive G forces which will force blood in the
extremities to the digits. This is a tricky situation, because it the limbs
fly out with digits outwards, then the inertial reaction will tend to force
blood out from the torn vessels at the proximal end, rather than digitwards.
If, on the other hand, limbs tumble and rotate somehow (quite possible with
wind drag and aerodynamic forces), then the blood may be pushed towards the
digits with considerable force and will cause rupture of capillaties and escape
of hemoglobin into extravascular space instantaneously. In this case, it does
not have to wait for hypoxic capillary permeability changes to occur.
Ultimately, the dark coloration which was noticed has to be due to either
reduced Hb per se, or one of its oxidation (not oxygenation) products. I quite
agree with Bish sir that this seems to be the most logical explanation.
Just to be morbid, I would have loved to have hypothesized that this phenomenon
was due to interaction of Hb or some other blood component with some exotic
chemical compound released during explosion, but the the magnitude at which the
torn limbs will be accelerated away from the centre of explosion precludes any
meaningful interaction of blood in that limb with any product of the explosive
compounds. A most ridiculous notion. Don't give it another thought.
Sudhanshu
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