Links between traumatic brain injury and ballistic pressure waves originating in the thoracic cavity and extremities

TL;DR

This paper reviews evidence that pressure waves from gunshot impacts distant from the brain can cause traumatic brain injury, highlighting the importance of pressure wave magnitude in injury risk assessment.

Contribution

It synthesizes experimental, epidemiological, and case study data to support the hypothesis that ballistic pressure waves can induce TBI without direct brain trauma.

Findings

Bullet impacts distant from the brain produce pressure waves of 18-45 psi in the brain.

Pressure waves of 15-30 psi can cause mild to moderate TBI in animal models.

High correlation (r > 0.9) between pressure wave magnitude and rapid incapacitation in humans.

Abstract

Identifying patients at risk of traumatic brain injury (TBI) is important because research suggests prophylactic treatments to reduce risk of long-term sequelae. Blast pressure waves can cause TBI without penetrating wounds or blunt force trauma. Similarly, bullet impacts distant from the brain can produce pressure waves sufficient to cause mild to moderate TBI. The fluid percussion model of TBI shows that pressure impulses of 15-30 psi cause mild to moderate TBI in laboratory animals. In pigs and dogs, bullet impacts to the thigh produce pressure waves in the brain of 18-45 psi and measurable injury to neurons and neuroglia. Analyses of research in goats and epidemiological data from shooting events involving humans show high correlations (r > 0.9) between rapid incapacitation and pressure wave magnitude in the thoracic cavity. A case study has documented epilepsy resulting from a pressure wave without the bullet directly hitting the brain. Taken together, these results support the hypothesis that bullet impacts distant from the brain produce pressure waves that travel to the brain and can retain sufficient magnitude to induce brain injury. The link to long-term sequelae could be investigated via epidemiological studies of patients who were gunshot in the chest to determine whether they experience elevated rates of epilepsy and other neurological sequelae.