Thursday, January 29, 2015
I've been getting some questions about the concept of fixed lividity/livor mortis so I thought that I'd do a quick introductory post on the matter.
When blood settles to the bottom, it stays there. After it's there for a long time, the pattern becomes "fixed," i.e., when you press your finger into the skin, the skin doesn't blanch much. Try this on your hand right now...push your finger deep into the skin. The skin will blanch (turn white) as the blood moves away from the pressure. If the lividity pattern is fixed or close to fixed, the blood won't want to move, so the skin won't blanch much. Whether or not the pattern is fixed helps us to determine how long you've been dead.
According to Howdunit Physics,
The ME can use shifting and fixed lividity to estimate time of death and to determine if the body has been moved or repositioned, something the dead do not do with assistance.
If a body is found face-down with fixed lividity along the chest, abdomen, and front of the legs, the ME can conclude that the death was at least six to eight hours earlier. It may be longer but it is not likely sooner. If the lividity can still be shifted, death likely occurred less than four hours or so earlier. On the other hand, if a body is found face-down, but with fixed lividity along the back, then the body was moved at least six hours after death, but not earlier or the lividity would have shifted to the newly dependent area. This means the body lay on its back for at least six hours after death, long enough for the lividity to become fixed, and was then rolled to its stomach or moved to an entirely different location and deposited on its stomach.
Therein lies the most common use of evidence of "fixed lividity" in a corpse: If the "fixed lividity" in a corpse doesn't match the burial position, it means (1) the body likely wasn't buried until at least 6-8 hours after death unless the body was in a position consistent with the fixed lividity prior to burial; or (2) the body was repositioned after initial burial.
For instance, check out the following excerpt from State v. Dreher, 695 A.2d 672, 682 (N.J.App. 1997):
[Chief Medical Examiner Ernest] Tucker noted that liver mortis begins within thirty minutes of death and continues for the next couple of hours. Once lividity becomes fixed, a red or pink area on the skin will not blanche even when pushed. Fixed lividity, which was demonstrated in this case, requires a minimum of six hours. Tucker noted, however, that there was a portion of the lividity that was inconsistent with the position of the body as found. There was lividity along the victim's right leg and buttocks, which suggested that the body may have been moved after death. The time required for lividity to redistribute itself is longer than the time required for it to develop in the first place.