Because of the cessation of blood flow at death, there is gravitational settling of blood that distends capillaries and veins, resulting in discoloration of skin in the non-compressed dependent areas of the body (Fig. 9). Slight hypostasis has been described in living individuals dying from a prolonged illness and terminal circulatory failure (4). Patchy lividity (1- to 3-cm or about 0.5- to 1-in. areas) has been described in nonde-pendent areas of the body and attributed to venous blood being squeezed to the skin surface by muscles undergoing rigor mortis (4). A sequence of changes has been described:
• Onset and progression: lividity first becomes apparent 20 min to 4 h after death (2,7). Discoloration is at maximum intensity from 3 to 16 h (7). At "fixation," lividity does not shift with a change of body position (time range = 6 to 12 h). Complete shifting occurs from 2 to 6 h and incomplete shifting (i.e., lividity partly persisting in the original location and changing according to a new position) is possible from 4 to 24 h (7). Fixation can
occur up to 3 d after death (7,29,30). Blanching of livid areas by thumb pressure occurs from 1 to 20 h (7,31).
Various mechanisms have been proposed to explain fixation. Blood, initially fluid, clots; however, the presence and time of occurrence of postmortem clotting are variable. Alternatively, there is diffuse extravasation of blood into soft tissues owing to vessel leakage, but this is also observed in nonfixed livor. Blood seepage is not consistently present in fixed lividity (1,30). Blood cannot shift from engorged capillaries because adjacent venous pressure is high (4). Another explanation is that unfaded lividity (fixed livor)
Fig. 9. Suicidal hanging. Suspension for unspecified period of time; lividity in dependent areas of arms and legs.
results from progressive hemoconcentration and red blood cell-clumping resulting from transudation of plasma from engorged vessels (30,32).
• Resolution: livor persists until decomposition occurs. The significance is as follows:
• The assessment of the degree of lividity can provide only an estimate of the time of death.
• The presence of livor, particularly if fixed, in the nondependent areas of a body at a death scene indicates that the body's position has been changed (1).
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