Noise is a very special item in a severe military operating environment. In addition to direct damage to the hearing system, it can also cause serious damage to multiple systems throughout the body. In recent years, with the rapid development of army's new equipment and weapons, officers' and soldiers' ratio to military noise has increased significantly. As an example, the percent of US Marines with NIHL increased by almost 68% in recent years. The Department of Veteran Affairs states that hearing loss and tinnitus are the third most common form of disability within the military, representing approximately 680, 000 individual cases. Hazardous noise exposure in the US military is greater than it has been in more than 30 years, with 30% of all post-deploying soldiers reporting noise exposure and 28% reporting corresponding hearing loss and/or tinnitus. While noise exposure is a staggering problem for deployed soldiers, it is also a problem for non-deployed soldiers. Recently, it was reported that 11% of Marines sustain hearing loss during basic training, despite the use of hearing protection. As all known, high level noise is the direct cause of acute acoustic injury. When officers and soldiers operate live ammunition, they produce high-intensity impulse sound. The blast wave generated by it can directly act on the human body and cause damage. The alternating overpressure and negative pressure in the blast wave are the main factors leading to hearing organs' damage. The instantaneous overpressure blast wave moves in the air at supersonic speeds, causing violent fluctuations in the lymph fluid in the labyrinth of the inner ear, which leads to mechanical damage and metabolic disorders such as basement membrane, vestibular membrane, and stria vascularis, and finally leads to hearing impairment。
Research by the U.S. military has shown that some veterans can tolerate hearing loss to a certain extent but can hardly tolerate long-term tinnitus. Not only does it sound like sleep, but it can also even cause hallucinations and depression, which seriously affects the quality of life. According to the statistics of officers and soldiers' symptoms after shooting training, tinnitus has the highest incidence, accounting for 56%, which is consistent with other literature reports. However, the degree of self-rating discomfort is lower, which may be related to most officers' and soldiers' shorter military age. In the classification of tinnitus sounds, low-frequency sounds are the most common, which may be related to conductive damage caused by strong impulse sounds.
This study shows that the probability of noise damage symptoms in service for more than two years is much higher than that of less than or equal to 2 years. Past studies have shown that the severity of noise-induced hearing loss increases with exposure time, which is consistent with this study's results. It is suggested that the noise exposure time should be reduced as much as possible during officers' and soldiers' training, and the prevention work should be focused on those who have served longer. Data shows that 18% of the U.S. military has significant noise-induced hearing loss. According to our survey, 38% of the officers and soldiers participating in shooting training have different noise-induced hearing loss degrees. This significant difference may be related to the lack of protective measures in our army. This survey shows that only 20% of the officers and soldiers wear HPD, which is much lower than that of foreign soldiers. In the foreign army,90% of the military wear HPD. Whether or not to wear HPD is highly correlated with the appearance of symptoms. This study shows that wearing HPD and asymptomatic accounted for 13.9% higher than those without HPD and asymptomatic. The difference is statistically significant, suggesting that wearing HPD is very important for preventing noise-induced hearing loss.
This study shows that blood type has a certain correlation with the population's susceptibility to noise. Among people with noise-induced hearing impairment after shooting, the proportion of blood type O appears the highest, which is higher than the proportion of blood type O (35.6%) compared to the total population participating in shooting training. The proportion of people who appear symptoms after shooting with type A blood is 24%, lower than that of the general population. Previous studies have shown that blood type, and noise susceptibility of people are related. Several previous studies have shown that blood type is highly correlated with people’s noise susceptibility. Blood type O is more susceptible to noise[7, 8]. However, in this study, there was no statistical difference in the proportion of people appear symptoms with type O blood and other blood types, which may be related to the particularity of the population under investigation. Simultaneously, the ratio of no symptoms with type A blood and no symptoms with other blood types appeared statistically significant differences. The difference suggests that type A blood may be more able to tolerate high-intensity noise.