The human body undergoes a series of changes following death, with lividity, also known as livor mortis or postmortem hypostasis, being a significant early post-mortem change. This phenomenon involves a discoloration of the skin, offering forensic investigators valuable insights into the circumstances surrounding an individual’s death.
How Lividity Develops
Lividity arises from a biological and physical process that begins once the heart stops circulating blood. Without the heart’s pumping action, blood within the vessels becomes stagnant. Gravity then causes heavier red blood cells to settle in the capillaries and small veins of the lowest, or dependent, parts of the body, leading to characteristic skin discoloration. Simultaneously, areas of the body pressed against a hard surface, like the ground, will not show lividity due to capillary compression. This creates areas of pallor, known as contact pallor or contact blanching, within the discolored regions.
Stages and Appearance
Lividity typically presents as a reddish-purple discoloration on the skin. It often begins to appear as faint, patchy areas within 30 minutes to 2 hours after death. These initial patches can increase in size and intensity, forming broader, more uniform areas of discoloration within approximately 3 to 4 hours. The intensity of the color depends on the amount of reduced hemoglobin in the pooled blood.
Lividity progresses through distinct stages: “blanching” (unfixed) and “non-blanching” (fixed). In the early, unfixed stage, pressure applied to the discolored area temporarily pushes the pooled blood away, causing the skin to blanch. Once pressure is released, the color returns. Lividity typically becomes fixed, meaning it no longer blanches under pressure, approximately 8 to 12 hours after death, as blood cells begin to clot and leak into surrounding tissues. The color can also vary; for instance, carbon monoxide poisoning may result in a cherry-red lividity, while hypothermia can cause a pinkish hue.
Forensic Insights
Lividity offers important clues in forensic investigations, primarily aiding in estimating the post-mortem interval and determining if a body has been moved. Investigators can press on an area of lividity to determine if it blanches, which indicates the approximate time elapsed since death. Unfixed lividity suggests a shorter post-mortem interval, usually within the first few hours.
The distribution pattern of lividity is crucial for determining the body’s position at the time of death and any subsequent post-mortem movement. Blood pools in the parts of the body closest to the ground; for example, a person dying on their back would show lividity on their posterior surfaces. If a body is found in a position inconsistent with the observed lividity pattern, it suggests the body was moved after lividity began to form but before it became fully fixed. For instance, if lividity is fixed on a body’s back but it is found lying face down, it indicates the body was originally supine and later moved.
Distinguishing lividity from bruising is also important in forensic pathology. Lividity involves blood remaining within the vessels, whereas a bruise indicates blood has extravasated, or leaked, out of damaged vessels into surrounding tissues, a process requiring active circulation. Pathologists differentiate them by examining tissue samples microscopically for signs of vital reactions, such as inflammation, which are present in bruises but absent in lividity.
Variables Affecting Lividity
Several factors can influence the development, appearance, and timeline of lividity. Internal factors related to the deceased include blood volume and cause of death. For example, individuals with severe blood loss or anemia may exhibit less pronounced lividity, or its development might be delayed. Certain causes of death, like asphyxia, can lead to a darker purplish lividity due to deoxygenated blood, while carbon monoxide poisoning results in a characteristic cherry-red color.
External factors, particularly ambient temperature and pressure points, also play a significant role. Cooler temperatures can slow the onset and development of lividity, potentially delaying its fixation. Conversely, higher temperatures may accelerate the process. Tight clothing or surfaces pressing against the body can create areas of contact pallor where lividity does not form, offering additional clues about the body’s position.