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a purple coloration of dependent parts, except in areas of contact pressure, appearing within 30 minutes to 2 hours after death, as a result of gravitational movement of blood within the vessels.
postmortem hypostasisThe red-purple colouring of the skin surface which appears on dependent body parts after circulation has ceased and gravity pulls the now-stagnant blood to the lowest points of the body. The dark red-purple background may be punctuated with whitish areas, corresponding to areas on which the body was resting at the time of death, which compress the blood vessels and prevent hypostasis in those areas. Postmortem hypostasis is due to the formation of oxyhaemoglobin at the expense of reduced haemoglobin.
Bruises rarely cover the large areas covered by hypostasis, which often have horizontal margins and bloodless zones due to tight clothing. Bruises may be accompanied by abrasions, often have discoid contours, or irregular margins, and lack bloodless zones. With time, distinguishing the two becomes impossible.