Acoustic trauma is an injury to the inner ear that’s often caused by exposure to a high-decibel noise. This injury can occur after exposure to a single, very loud noise or from exposure to noises at significant decibels over a more extended period of time. Shooting exercise is a curriculum at Sekolah Polisi Negara (SPN). Acoustic trauma incidence post gunshot exposure at SPN was quite high. A study of 100 East Java SPN students showed an incidence of 15% acoustic trauma. While other studies on 100 Bali SPN students showed an incidence of 11% acoustic trauma. The gunshot exposure could create oxidative stress in the cochlea as a result of free radicals release. Oxidative stress occurred due to the imbalance between free radicals and antioxidants, where the free radicals were distinctly dominant. Oxidative stress could cause lipid peroxidation process, increased MDA level and hair cells damage which started at a high frequency
The mechanical process caused the rupture of hair cells, basilar membranes, and hydrolymphatic membranes, which are essential components of the inner ear that function to transmit sound vibrations. Constant gunshot exposures could cause cochlear damage as a result of the metabolic process. This occurs due to a disruption in the balance of calcium and hypoxia in the cochlea, which later results in an increase in free radicals and a state of oxidative stress. The free radicals in question are Reactive Oxygen Species (ROS). ROS will cause damage to the cell membrane and lead to the death of the cochlea hair cells. The hearing disturbance caused by this process is manifested by an increase in the hearing threshold value, which means that the hearing sensitivity decreases.
Antioxidants are produced naturally endogenic to suppress free radicals in a specific condition, for instance in a constant gunshot exposure, where free radicals were still more dominant than antioxidants, thus, arising oxidative stress.14,15 A research in Turkey in 2008 reported the increase of MDA post gunshot exposure.1 A study in Bandung in the year 2015 reported MDA increased level and an increase in acoustic trauma incidence in a placebo group compared to a group of orally given peroxidase glutathione antioxidants. However, the correlation between MDA level and hearing threshold level at frequency 4000 Hz post gunshot exposure in East Java SPN students was still unclear.\. Therefore, Dr. dr. Nyilo Purnami, Sp.THT-KL (K), FICS, FISCM as the principal author, along with dr. Fauzi Helmi and Prof. dr. Sri Herawati, Sp.THT-KL (K) conducted a study to determine the relationship between MDA levels and the frequency hearing threshold value of 4000 Hz after exposure to gun eruptions among SPN East Java students. The research data used was taken from 50 medical records of SPN East Java students class 2017/2018. The medical records used have complete history, physical examination, audiogram, and MDA level examination, which were carried out two weeks after the last shooting practice. MDA measurement is done by taking blood that is done two weeks after the last shooting practice. The participating students have participated in shooting training for five months, with a total of 100 shots using long guns (rifles and shotguns) and 100 shots using short guns (revolvers and pistols). The range of shooters was very close and consisted of 20 students per group. Ear protection equipment is not used regularly.
The results showed that only one student complained of hearing loss. The explanation for this result is due to the temporary and permanent threshold shift. Noise can cause damage to the stereociliary ends and actin filaments of stereocilia. The damage to the stereocilia ends will be repaired in 24 – 120 hours, while the damage to the stereociliary actin filaments will be repaired in 48 hours. There is also the stiffness of the outer hair cells which will improve in 2 weeks. In this study, data were collected 2 weeks after the last exposure. These things cause almost all students to experience only a temporary shift in the hearing threshold in this study. Meanwhile, the shift in the permanent hearing threshold only occurred in one student.
Research also shows that the higher the MDA level after being exposed to a firearm explosion, the higher the hearing threshold value at a frequency of 4000 Hz. However, keep in mind that MDA levels themselves can be affected by several conditions such as inflammatory processes and a history of taking previous antioxidants. This study is supported by previous research, which shows an increase in the hearing threshold value at high frequencies, especially at a frequency of 4000 Hz. This study, which was conducted by Dr. Nyilo, showed a decrease in the hearing threshold value at a frequency of 4000 Hz, which was indicated as acoustic trauma in 28 students (56%).
The use of earplugs as an effort to prevent acoustic trauma has been carried out, but it is not very effective in reducing the intensity of exposure. Therefore, other methods are needed to prevent acoustic trauma. Free radicals are becoming a new target in efforts to prevent acoustic trauma. The hope is, by consuming antioxidants as an additional therapy, it can prevent acoustic trauma in NES students.
Author: Dr. Nyilo Purnami, dr. Sp.THT-KL (K), FICS, FISCM
Detail information: Correlation Of Malondialdehyde And Hearing Threshold Level At Frequency 4000 Hz Post Gunshot Exposure https://www.orli.or.id/index.php/orli/article/view/283
