Abstract

Topicality: The training of military personnel for the performance of official duties includes training at ranges where shooting with various weapons is carried out. However, exposure to sounds of different intensity and character under certain circumstances can cause negative changes in the structures of the auditory analyser and the development of hearing disorders. An important element in the prevention of damage of the auditory system is the preservation of the function of sound conduction and the protective mechanisms of the structures of the middle ear. An objective method for determining the condition of the middle ear is the acoustic impedance method, acoustic stapedius reflex measurement which is widely applicated in the otolaryngology.

The exposure to high-intensity sounds in combination with a blast wave is something that military personnel face all the time in the course of their professional duties. Combat acubarotrauma is one of the most common manifestations of explosive trauma.

The purpose of the work: to investigate the indicators of acoustic impedance measurement in military personnel during shooting at the range.

Materials and methods: an examination was conducted of 72 servicemen who practiced the skills of shooting using machine-guns (Kalashnikov assault rifle without and with under barrel grenade launcher) in the conditions of the training ground. Fighters were examined before and immediately after shooting. The examination was carried out on an impedance tympanometer “Sentiero Desktop” PATH MEDICAL GmbH (Germany). During the conducting of impedance audiometry, we evaluated the threshold and amplitude characteristics of the acoustic reflex the shape and amplitude of the tympanogram.

Results and their discussion: Before the shooting, almost all examined servicemen had a type “A” tympanogram. In 2.7% of servicemen who did not complain of reduced hearing function, we recorded a tympanogram close to type “C”. The peak of the curve there was shifted in the negative direction, but such a shift did not exceed 50 mm of water column, which may indicate elements of auditory tube dysfunction. About 10% (9.7%) of patients had a high-amplitude tympanogram (type “Ad”). In 12.5% ​​of cases, we observed a reduced amplitude of the tympanogram of a normal form – “As” type, which can indicate both a hidden pathology of the middle ear and can be a variant of the norm. After the received sound load, the share of tympanograms of type As increased to 16.6%, and Ad – to 12.5%.

When examining the threshold of acoustic reflex in the examined servicemen, no significant difference was found between the indicators obtained both before and after sound exposure, as well as compared to the control. Thus, the parameters of acoustic reflex thresholds during ipsilateral stimulation before firing were 86.7±2.1 dB, after – 90.1±2.2 dB. Acoustic reflexes on both sides were registered in all subjects before the sound load. In 12,5% ​​of cases, the amplitude of the registered response was slightly reduced. After shooting, the percentage of patients with reduced amplitude of ARVM increased to 16,6%.

The average statistical values ​​of the amplitude of acoustic reflex during ipsilateral stimulation were 0.19±0.02) cm³ before and 0.16±0.03 cm³ after firing, respectively. These indicators were significantly (p<0,01) not different from each other and from the control values.

Therefore, according to the data of impedance audiometry, there are no reliable changes in the quantitative indicators of tympanometry and acoustic reflex registration in military personnel before and after training firing.

However, some of the examined persons showed changes in the tympanogram after sound exposure – a certain smoothing of the top of the tympanometric curve and a decrease in its amplitude, an increase in compliance and a certain decrease in the amplitude of the ARVM. And 11,1% of the examinees reported a subjective noise in the ear and/or a feeling of blocked ears after the shootings. Part of the servicemen during the study felt discomfort and pain in the ear – 4,2% of the surveyed persons had such cases before the sound load, and 8,3% after. This sign may indicate increased reactivity of the protective mechanisms of the middle ear or certain manifestations of the phenomenon of accelerated volume growth, which, in turn, may reflect irritation of the auditory analyzer receptor.

We allocated all such persons to a separate subgroup 1, which included 57 people without any signs of pathology of the auditory system, and to 2 subgroup – 15 people who had complaints of blocked ears and/or subjective tinnitus after shooting; discomfort and pain during impedance audiometry; certain changes in the tympanogram and during registration of acoustic reflex.

Comparative analysis of impedance audiometry data in these selected groups showed that the amplitude of acoustic reflex and tympanogram compliance in the 2nd group of servicemen were significantly (p<0,01) reduced compared to the 1st and control groups.

The changes we found in the indicators of acoustic impedance measurement in military personnel after sound exposure at the training ground may indicate the exhaustion of the mechanisms of adaptation and adaptive reactions in response to high-intensity sounds.

Conclusions:

1. THE research using the method of impedance audiometry in military personnel who perform training shootings on the range contributes to the timely and objective detection of possible disorders of the protective mechanisms of the auditory system.
2. The results of acoustic reflex registration can be used to predict the possible development of sensorineural hearing disorders under the influence of high sound loads. The technique can be used to screen or determine the suitability of military personnel for duties in certain branches of the military (artillery) involving the use of explosive weapons.
3. About 10% of servicemen after conducting training firings at the firing range have some or other signs of hearing system reaction to sound load: complaints of blocked ears and/or subjective tinnitus after firing; discomfort and pain during impedance audiometry; decrease in tympanogram compliance and decrease in amplitude when registering acoustic reflex.
4. A change in the reactivity of the adaptive and protective mechanisms of the auditory analyzer under sound load in the form of the decrease or increase of the amplitude of the tympanogram and the decrease in the amplitude of the acoustic reflex can serve as an objective sign of an unfavorable prognosis regarding the development of sensorineural hearing disorders in military personnel when exposed to high-intensity sounds.

Keywords: battle trauma, blast injury, acoustic reflex, hearing loss, sensorineural hearing loss.