After death, the human body undergoes a series of changes, with one of the earliest and most noticeable being livor mortis, also known as lividity. This phenomenon involves a discoloration of the skin, offering insights into the post-mortem interval (time since death).
How Livor Mortis Develops
After the heart ceases to pump, gravity acts on the blood within the vessels. Red blood cells settle in the lowest, or dependent, parts of the body. This pooling of blood causes a purplish-red discoloration on the skin in these areas.
In its initial stages, within 30 minutes to 2 hours after death, this discoloration can be “blanched” or disappear when pressure is applied. This occurs because the blood is still contained within the vessels and can be pushed away. As time progresses, this discoloration can increase in intensity and spread, becoming more pronounced.
What Makes Lividity Fixed
Over several hours, the blood that has pooled in the capillaries undergoes further changes. The red blood cells begin to break down, and their contents leak out of the vessels and stain the surrounding tissues. Once blood leaks into the surrounding tissues, the discoloration becomes “fixed” or permanent. This means the lividity will no longer blanch or change color when pressure is applied, as the blood is no longer confined to the vessels.
The timeframe for lividity to become fixed ranges from 6 to 12 hours after death. Several factors can influence the speed and appearance of fixed lividity. Warmer ambient temperatures can accelerate the process, while colder conditions may delay it. The volume of blood in the body also affects lividity’s prominence. Certain causes of death can affect the color of lividity; for instance, carbon monoxide poisoning often results in a cherry-red or bright-pink lividity due to the formation of carboxyhemoglobin.
Its Role in Forensic Investigations
Fixed lividity provides information in forensic investigations, primarily aiding in two areas: estimating the time of death and determining if a body has been moved. The presence, extent, and fixation of lividity can help forensic investigators establish a post-mortem interval (PMI), offering a range rather than an exact moment of death. If lividity is still blanchable, it suggests a shorter PMI (less than 8 hours), whereas fixed lividity indicates a longer period since death.
The distribution patterns of fixed lividity are also used to understand the body’s position at the time of death. Blood pools in the dependent areas, so if a body was lying on its back, lividity would be observed on the back. If the lividity pattern is inconsistent with the position in which the body is found—for example, a body found face down with fixed lividity on its back—it suggests the body was moved after lividity became fixed. This indicates the body remained in its initial position long enough for the lividity to become permanent before being repositioned.