IndAeMed_F: Re: Postmortem lividity

  • From: USM Bish <bish@xxxxxxxxxxx>
  • To: indaemed@xxxxxxxxxxxxx
  • Date: Sat, 3 Apr 2004 20:47:09 +0530

Thru IndAeMed@xxxxxxxxxxxxx:
   On Fri, Apr 02, 2004 at 09:42:50PM +0500, ssmhialt@xxxxxxxx wrote:
> To my mind, there is no doubt that what Dilish has described is
> typical post mortem lividity ....

[ For once Mish and Bish are  singing the same tune. So much of
the mail has been snipped off !]

> 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. 

The term "Explosive G forces" is perhaps a bit misleading. What
happens in  an explosive fragmentation is  physical disintegra-
tion of tissue components within fractions of a second. It is a
shock wave of  immense magnitude for a very  short pulse, which
rip  through the  tissues  followed by  an  evergy void  state.
Depending  upon the  type of  explosion, there  may be  "after-
waves" of  a decaying  sinusiodal pressure  pattern. It  may be
noted that because of release of high amount of energy within a
very short time  span, it is invariably followed  by an intense
thermal   wave,   which  contributes   significantly   to   the
instantenous  chemical  interactions, notably,  oxidation  with
oxygen being  provided from  the air.  It is  pure physics  and
chemistry out here. No physiology. 

The moment forces exceed the stuctural strength of tissues they
fragment  along  the  lines  of  least  resistace,  with  total
structural  disintegration,  partially  modified  by  available
clothing. There is no time for  hydrostaic shifts, or G induced
vascular  changes.  Any  and every  cell  may  be  structurally
damaged  with the  pressure  pulse,  so obviously  things  like
hypoxic pemeability changes as brought  out by Mish are perhaps
non-issues.  It is  a  state of  oxidation  and other  chemical
processes  (depending  upon  the  type  of  explosion  and  the
immediate environment)  which would  govern the  final chemical
composition and state of the remnant tissues.

This is NOT lividity as explained in Forensic texts (which is a
hydrostatic  force based  phenomenon),  rather,  a state  after
physical and  chemical disintegration, due to  forces explained

As doctors, we have a natural  tendency to find explanations as
per principles of  physiology and pathology, but  in situations
like this, it is absolute basics of physics and chemistry which
may provide a better explanation.

Just my POV


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