A blast injury is a complex type of physical trauma resulting from direct or indirect exposure to an explosion. Primary injuries are especially likely when a person is close to an exploding munition, such as a land mine. Additionally, the intensity of the pressure changes from the blast can cause injury to the blood vessels and neural pathways within the auditory system. Therefore, affected individuals can have auditory processing deficits while having normal hearing thresholds. The combination of these effects can lead to hearing loss, tinnitus, headache, vertigo (dizziness), and difficulty processing sound. These injuries may affect any part of the body and sometimes result in penetrating trauma with visible bleeding. High-order explosives produce a supersonic overpressure shock wave, while low order explosives deflagrate and do not produce an overpressure wave. A blast wave generated by an explosion starts with a single pulse of increased air pressure, lasting a few milliseconds. The negative pressure (suction) of the blast wave follows immediately after the positive wave. The duration of the blast wave depends on the type of explosive material and the distance from the point of detonation. The blast wave progresses from the source of explosion as a sphere of compressed and rapidly expanding gases, which displaces an equal volume of air at a very high velocity. The velocity of the blast wave in air may be extremely high, depending on the type and amount of the explosive used. An individual in the path of an explosion will be subjected not only to excess barometric pressure, but to pressure from the high-velocity wind traveling directly behind the shock front of the blast wave. The magnitude of damage due to the blast wave is dependent on the peak of the initial positive pressure wave, the duration of the overpressure, the medium in which it explodes, the distance from the incident blast wave, and the degree of focusing due to a confined area or walls. For example, explosions near or within hard solid surfaces become amplified two to nine times due to shock wave reflection. As a result, individuals between the blast and a building generally suffer two to three times the degree of injury compared to those in open spaces. and brain damage, with potential neurological and neurosensory consequences. It is a complex clinical syndrome caused by the combination of all blast effects, i.e., primary, secondary, tertiary and quaternary blast mechanisms. Blast injuries usually manifest in a form of polytrauma, i.e. injury involving multiple organs or organ systems. Bleeding from injured organs such as lungs or bowel causes a lack of oxygen in all vital organs, including the brain. Damage of the lungs reduces the surface for oxygen uptake from the air, reducing the amount of the oxygen delivered to the brain. Tissue destruction initiates the synthesis and release of hormones or mediators into the blood which, when delivered to the brain, change its function. Irritation of the nerve endings in injured peripheral tissue or organs also contributes significantly to blast-induced neurotrauma.

Individuals exposed to blast frequently manifest loss of memory of events before and after explosion, confusion, headache, impaired sense of reality, and reduced decision-making ability. Patients with brain injuries acquired in explosions often develop sudden, unexpected brain swelling and cerebral vasospasm despite continuous monitoring. However, the first symptoms of blast-induced neurotrauma (BINT) may occur months or even years after the initial event, and are therefore categorized as secondary brain injuries. The broad variety of symptoms includes weight loss, hormone imbalance, chronic fatigue, headache, and problems in memory, speech and balance. These changes are often debilitating, interfering with daily activities. Because BINT in blast victims is underestimated, valuable time is often lost for preventive therapy and/or timely rehabilitation. The study found molecular changes consistent with neuroinflammation and vascular damage in service members who were exposed to repeated low-level blasts.

Blast wave PTSD research

In addition to known post-traumatic stress disorder (PTSD) risk factors experienced by both civilians and military personnel in combat areas, in early 2018, 60 Minutes reported that neuropathology specialist, Dr. Daniel "Dan" Perl, had conducted research on brain tissue exposed to traumatic brain injury (TBI), discovering a causal relationship between IED blast waves and PTSD. Perl was recruited to the faculty of the Uniformed Services University of the Health Sciences as a professor of pathology and to establish the Center for Neuroscience and Regenerative Medicine mandated by Congress in 2008. In 2006, researchers found that many of the symptoms of PTSD, overlap with those of TBI, potentially leading to misdiagnosis in individuals who have experience blast injury.

Casualty estimates and triage

Explosions in confined spaces or which cause structural collapse usually produce more deaths and injuries. Confined spaces include mines, buildings and large vehicles. For a rough estimate of the total casualties from an event, double the number that present in the first hour. Less injured patients often arrive first, as they take themselves to the nearest hospital. The most severely injured arrive later, via emergency services ("upside-down" triage). If there is a structural collapse, there will be more serious injuries that arrive more slowly.

See also

  • Battlefield medicine
  • Blast-related ocular trauma
  • Suicide attack
  • Total body disruption

References

General

  • Blast injury information from the CDC
  • Blast injury primer for clinicians