Also known as explosive deafness, it is an injury caused by intermittent impulsive noise from gunfire or bomb explosions. The noise is extremely intense, with a rapidly fluctuating spectral peak that rises and falls abruptly. The noise from automatic rifles can reach 174 dB, while cannons can reach 188 dB. When a cannon is fired, it instantly generates a powerful positive pressure wave, with pressure reaching up to 3,000 kg/cm², lasting for 5 ms, followed by a negative pressure wave that can persist for 30 ms. Collectively, these are referred to as pressure waves. Such intense noise and shock waves are most likely to cause auditory function damage.

bubble_chart Etiology

1. Mechanical injury: A sudden strong positive pressure wave causes the tympanic membrane to rupture. According to experiments, the critical perforation pressure of the tympanic membrane is 0.18 kg/cm². A positive wave as high as 3000 kg/cm² can rupture the tympanic membrane, displace the auditory ossicles, and cause hemorrhage in the tympanic cavity. Through the action of the ossicular chain and the cochlear window on the perilymph and endolymph, it can induce violent fluctuations in the endolymph, leading to necrosis and degeneration of the spiral organ and hair cells.

2. Metabolic disorder: Blast exposure reduces the activity of SDH (succinate dehydrogenase) and MDH (malate dehydrogenase) in hair cells, causes swelling of vascular endothelial cells, obstructs blood flow, and leads to cellular degeneration. The blast wave can also cause rupture, hemorrhage, and crush injuries in other parts of the body. The greater the peak of the blast wave, the longer the exposure time, or repeated injuries, the more severe the damage. Depending on the degree of injury, the tympanic membrane may exhibit static blood, cloudiness, or perforation. The damage to the middle ear and inner ear may vary, with severe middle ear injury but only mild inner ear injury.

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The instantaneous reaction to exposure to a blast wave is immediate auditory fatigue and an increase in hearing threshold, known as temporary threshold shift, which is a reversible change. Normal hearing can recover after resting for 1 to 2 hours, though sometimes it may take several days or weeks to fully restore. Due to differences in the position of sound exposure, the hearing impairment between the two ears can differ by 20 dB. The injury zone first manifests as a hearing dip at 6 kHz, which is twice as common as at 4 kHz. If repeatedly exposed to blasts, it can lead to an irreversible permanent threshold shift, resulting in permanent deafness. According to Wang Boti's (1982) survey during the Sino-Vietnamese border conflict, sensorineural deafness occurred in 59.9% of cases, mixed deafness in 8.9%, and psychogenic deafness in 0.5%. In cases of acute injury, many report severe ear pain and tinnitus, with half experiencing headaches and vertigo. Due to vestibular membrane detachment and degeneration, vertigo may sometimes resemble Ménière's disease or positional vertigo, lasting from several months to years.

bubble_chart Treatment Measures

A tympanic membrane perforation of 70% can heal on its own. Be careful not to allow water to enter the external auditory canal. Oral antibiotics and sulfonamides can be used to prevent infection. For cases where the perforation does not heal, ossicular dislocation, or fractures occur, tympanoplasty may be performed. For early deafness, vasodilators and neurotrophic drugs should be used. Wang Boti reported that integrated Chinese and Western medicine treatment achieved an efficacy rate of 80% within one month post-injury and 68% after six months. The Chinese medicinals used include Pueraria Root, Sichuan Lovage Rhizome, Dipsacus, Bupleurum, Magnetite, Codonopsis, and Acorus, each 15g, with Liquorice Root 10g, decocted in water and taken once daily. Additionally, ferrous sulfate 0.6g three times a day and other vitamins were administered. For persistent headache and dizziness, sedatives and drugs for soothing nerves and harmonizing collaterals can be used.

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Blast injuries often occur during wars, so it is essential to improve weapons, reduce the intensity of blast noise, and strengthen defensive fortifications. Soldiers should be trained to adopt protective postures during combat. When firing guns or detonating explosives, they should practice open-mouth breathing and swallowing to facilitate the opening of the eustachian tube. Protective earplugs and helmets should be utilized. Several models of protective earmuffs and helmets are already available domestically, such as the V-51R earplugs and JW-2 earplugs.