Wounding Mechanism

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In general, there are three different types of damage processes caused by firearm projectiles.

1. Slow Speed Single projectiles are able to push their way into interior organs. Unless the muzzle is in a firm contact position, there is little chance of cavitation forming. The bullet goes through the liver in a continuous path, generating a hole and passage with a diameter that is nearly identical to the projectile’s. Organs like the brain, lung, spleen, and kidney are no exception. The track’s inside edges may be brittle and regularly filled with blood. The course will be altered by bullet fragmentation and jacket separation.

2. Projectiles with a High Velocity, Because the bullet is travelling at or above the speed of sound, a temporary cavity will most likely form. The physics are based on a compressed air wave moving forward. The cavity can be up to 40–60 times the projectile’s diameter and can last several milliseconds. After that, the cavity collapses, leaving a ragged uneven defect that represents the projectile’s passage. Kinetic energy is spent by radially disrupting the projectile track even more dramatically. This is particularly true in organs like the liver. The parenchyma will be pulped and fragmented during the post mortem examination. It’s possible that a well-defined bullet trace won’t be found in some circumstances. There’s also the issue of massive amounts of hot gas under great pressure in hard or near-contact shots. If the bullet has a soft end, it may shatter almost completely, resulting in the famous “lead snow storm” appearance on X-ray. If the projectile is fully jacketed, it should be able to exit the body with little to no deviation in trajectory. Secondary projectiles can be launched and exit separately from the bullet.

3. Smooth bored close or contact shot, may have an explosive consequence. The pellet aggregate exits as a solid mass, but after passing through skin and muscle, it easily separates. The pellets then travel outward, frequently at random, shredding all tissues in their path. The consequent soft tissue damage is tremendous, especially when combined with the large expulsion of hot gases under severe pressures. Let’s look at the major organ systems to see the respective wounds mechanisms.

CENTRAL NERVOUS SYSTEM
The brain is a delicate organ with few connective structures that support it. To some extent, the intraparenchymal vessels tend to hold the organ together. Bullets may leave a well-defined track in the brain, or they may cause enormous pulping, or even whole or partial exenteration. A direct hit to key places like the brainstem might result in sudden death. Internal ricochet may cause the projectile to rebound from the inside table of the skull, causing extensive injury. Massive bleeding will ensue if cardiac output is maintained for an extended period of time. Subarachnoid hemorrhage with intraparenchymal/intraventricular distribution is most likely. Death may be delayed if the projectile hits a nonvital location, such as the frontal lobe.

The effects of cumulative internal bleeding and cerebral edema may cause the victim to die. If a person survives, they may have delayed consequences such as epilepsy, meningitis, and mental disability. The concussive power of a bullet striking a nonvital location, on the other hand, could be enough to injure the brainstem. Autopsy frequently reveals petechial hemorrhages in the brainstem.

Small bone fragments and fine lead particles are typically found in bullet tracks at autopsy, which can be seen on X-ray.

The spinal cord can be lacerated, transected, or contused, causing motor and sensory impairment in varied degrees.

CARDIOVASCULAR SYSTEM

The epicardium and myocardium may be grazed or the missile may pass through the heart. Blood will be expelled under pressure and enter the pericardium or hemithorax if the chambers are ruptured. As previously stated, a direct shot to the heart may not be lethal right away. For a brief while, the victim may have some potential for revenge or defense. Low-velocity bullets can enter the atria or right or left ventricles. The left ventricular wall is significantly thicker than the right ventricular wall. The flaw produced by the bullet may indeed operate as a valve due to the pliable and elastic qualities of muscle.

Despite the greater pressure differential on the left side, a perforating shot to the right ventricle often results in less blood loss internally. The comparatively thin right ventricular wall may gape, releasing more blood despite being under lower hemodynamic pressure.

At close range, high-velocity rounds and smooth bore discharges usually produce massive devastation, which is generally characterized by pulping and laying open of all four chambers. Hemothorax is when blood collects in the chest cavity, which can lead to lung perforation and collapse (hemopneumothorax).

The projectile may occasionally graze a coronary artery, causing cardiac tamponade in the form of a hemopericardium.

The aorta is a flexible organ while young, but as it ages, it becomes calcified and brittle. It is easy for low-velocity bullets to pass through it, creating microscopic slit like lacerations. High-velocity bullets and smooth bore discharges have the potential to completely damage the aorta. It’s possible that the ends are shredded and dispersed. If the aorta is the sole major organ that is destroyed, there will be a lot of internal blood loss, which will lead to hemodynamic shock and death. Hemorrhage may collect in a prepared cavity (hemithoraces) or in the retroperitoneal soft tissues, with the latter resembling the aftermath of a ruptured aneurysm.

RESPIRATORY SYSTEM

Blood rapidly enters the lumen of a “uncomplicated” tracheal lesion, which can subsequently be inhaled into the minor airways. Suffocation can occur as a result of blood aspiration, which leads to pulmonary edema and death. Given enough projectile velocity and impact pressure, the trachea may also break.

Single low-velocity projectiles leave well-defined holes in the lung’s visceral pleura, which may or may not be exited. There is usually a lot of intraparenchymal bleeding and a lot of edema.

A tension pneumothorax or a hemopneumothorax is a common occurrence.

In contrast to the brain, the pulmonary parenchyma has a lot of supporting connective tissue and is a naturally vascular organ. It’s possible that death won’t happen right away. Gunshot wounds to the chest that only involve the lungs are often recoverable with immediate surgery.

GASTROINTESTINAL TRACT
In various writings, the liver has been addressed in passing and is frequently regarded as a “organ of example.” The.22 caliber projectile frequently leaves a well-defined trace with slightly flimsy inside margins. In many situations, especially if the liver is hardened by illness, “beveling” can be seen near the point of exit. Hepatic damage usually results in a gradual internal hemorrhage that can be treated with surgery right away. The tissue is pulped by high-velocity and smooth-bore discharges, resulting in substantial blood loss, cardiogenic shock, and death. Large areas of cavitation and lacerations that split are typical. Every surgeon will attest to the fact that the liver is fragile by nature. At autopsy and especially after histological study, liver emboli might be observed in pulmonary arteries.

The projectile’s “uncomplicated” passage may perforate the hollow viscera (stomach, intestines, and gallbladder). The entrance and departure sites are unremarkable.

The lesion may be surrounded by localized serosal and mesenteric bleeding in survivors.

Multiple entry, exit, and reentry abnormalities are prevalent at autopsy due to the anatomical distribution of the large and small intestinal loops. Unless the major vasculature is damaged, death is rarely quick. Death from peritonitis is a potential conclusion if surgery is not performed, which can take several days. High velocity and smooth bore discharges can
cause gross disruption to these structures.
GENITOURINARY SYSTEM

For all intents and purposes, the kidney functions similarly to the liver. Splitting lacerations with substantial bleeding can be expected, albeit they are less likely to pulp. The kidneys are located in the retroperitoneal cavity. Hemorrhage can be significant, although it’s usually contained in the fatty and connective tissues.

The bony pelvis protects the bladder, but it is vulnerable to rupture if it is overfilled with pee. Should the pelvis be broken by bullet contact, secondary bone projectiles are likely to perforate the muscle wall of the bladder. The uterus is sometimes involved in gunshot wounds.

The organ is naturally more noticeable in the gravid uterus. There have been numerous examples of intrauterine gunshot damage that resulted in both maternal and foetal death.

RETICULOENDOTHELIAL SYSTEM
The spleen is a substantial but delicate organ that is susceptible to pulverization and laceration splits. The spleen is a circulatory organ that, if damaged, can result in significant hemorrhage. It’s an intraabdominal hemorrhage. Trauma can cause damage to surrounding organs like the pancreas, stomach, and diaphragm. The trauma caused by high-velocity and close-range shotgun rounds can fracture the spleen completely, rendering it nearly unrecognizable.

REMOTE EFFECTS
On rare situations, bullets may embolize. This is potentially feasible following injuries to highly vascular organs like the liver, or huge blood vessels like the aorta (and its branches) and vena calvae. On X-ray, the bullet may be observed in a location other than the expected point of rest. Bullets can be swept along artery or venous ramifications with enough “vis a tergo.” A bullet that enters the aorta lumen may be swept into a common iliac artery before striking and occluding the popliteal artery. Tissue fragments (soft organ parenchyma, bone marrow, and bone spicules) are also capable of travelling long distances. The immediate and long-term consequences differ depending on the final organ of impact.