1. Introduction

Workers at most enterprises of aviation industry, heat and hydropower are exposed to a complex of unfavourable factors of industrial environment, among which the phenomena of physical nature occupy one of the leading places. Affecting the human body, they are capable of producing biological effects that affect its well-being, efficiency and health, up to the development of certain diseases. Morbidity at such enterprises is mainly caused by work in conditions of vibration and noise. According to the authors' data, the rates of occupational morbidity in the aircraft industry and power engineering in the Irkutsk region were in different years: 7.8-49.3 and 0.9-6.9 per 10 thousand workers; in the Republic of Buryatia -6.2-34.0 and 0-4.02 per 10 thousand workers, respectively [1,3,7]. It is known that exposure to vibration and noise leads to tension of non-specific compensatory mechanisms in the human body. Recent advances in haematology and immunology create opportunities to search for specific immunological mechanisms involved in the occurrence and development of various pathologies under the influence of physical factors on the body. A number of researchers in persons with vibration-dangerous occupations have established a violation of the activity of various systems of the organism, which later were confirmed in experimental works on animals [2,5]. However, the data on the effect of vibration on haematological and immunobiological parameters, which are the basis of various changes in the organism, are very limited and contradictory. By the present time, the idea that among a significant number of life-supporting systems, the immune system fulfils protective, censor, regulatory, and regeneration stimulating functions has been finally formed. All the above-mentioned determined the purpose of the study - to analyse the data concerning the natural reactivity of the organism of workers due to the impact of vibration and noise [4,6,8].

Anichin V.F. in 2014 in his work proved that under the influence of noise there are changes not only in the receptor, but also in the brainstem region, where the conductive pathways of the auditory analyser pass. Studies in recent years have also shown that pathological processes in the brainstem region cause changes in the latency values of the peaks of short-latency auditory evoked potentials [1], According to EEG data, some authors have identified changes in the subcortical structures of the brain in workers with occupational hearing impairment.

2. Purpose of the Study

To investigate short-latency auditory evoked potentials in hearing disorders of noise aetiology.

3. Materials and Methods

We studied a group of 25 patients in the period 2022 - 2023. The studies were conducted in Samarkand metallurgical plant, our studies were carried out on a specialised complex of MK-6 equipment of "Amplaid" company (Italy). CSVP registration was carried out in response to sound clicks of 100 µs duration, intensity 50, 50 and 70 dB above the subjective threshold of audibility of clicks. Ipsilateral potential withdrawal was used. Of those examined, 25 young, otologically healthy individuals aged 19 to 25 years who had previously worked in noise conditions (control group) and 45 workers in noise occupations with hearing impairment by the type of damage to the sound-receptive apparatus were studied. The age of the persons in the main group ranged from 22 to 51 years, and work experience in noise conditions ranged from 2 to 33 years, the level of the latter in industrial premises was 90-95 dBA. Persons with asymmetrical hearing impairment and conductive hearing loss were not included in the main group. According to the degree of hearing loss, the examined persons were subdivided into three groups: Group 1 consisted of 14 people with bone and air conduction hearing impairment in high frequencies up to 20 dB; Group 2 - 13 with hearing loss in high frequencies from 20 to 50 dB and Group 3 - 18 patients with hearing loss from 50-70 dB. At the same time, intelligibility of speech tests was preserved in them.

4. Results

We identified a control group where all CSVP waves were clearly defined and their latent periods decreased with increasing stimulus levels (Table 1).

Table 1. Latent periods of CWPS peaks in normal-hearing individuals and noise workers with hearing impairment

The inter-peak intervals I-III and I-V did not exceed the values characterising the normal state of the brainstem, and practically did not depend on the level of acoustic stimulation.

In the workers of group 1, the indices of latency periods of the CSVP peaks practically did not differ from those of normally hearing persons and the inter-peak intervals were on average within the normal range. However, one of them showed brainstem pathology, which was manifested by an increase in the inter-peak interval I-V of more than 4.4 ms.

In the workers of the 2nd group under equal stimulation conditions, an increase in the latent period of the V wave and inter-peak interval I-V was found. In addition, 4 of them showed an increase in the inter-peak I-V interval of more than 4.4 ms. It should be noted that the increase in the latent period is more pronounced for the late peaks of CSVP and at a stimulation intensity of 70 dB above the hearing threshold for wave V the lengthening is 0.53 ms compared to the values in the control group. In workers of the 3rd group an increase in the latent period of the V wave peak compared to the control by 0.67 ms at stimulation of 50 dB, by 0.75 - at 60 dB, by 0.76 - at 70 dB above the click hearing threshold was registered. The mean value of inter-peak interval I-V reached 4.65 ±0.05 ms at stimulation of 70 dB above the hearing threshold. In 12 individuals of this group an increase in the inter-peak interval I-V of more than 4.4 ms was determined. The dynamics of changes in the LPs of the CSVP peaks with increasing stimulation level in the workers of all 3 groups is similar to that of normal-hearing people, i.e. with increasing stimulation signal there is a shortening of the latency periods of the CSVP peaks. The obtained results show that the signs of pathological impact of noise on the human body, in particular on the brainstem structures, are manifested by changes in the latent peaks of CSVP and inter-peak intervals. They are most pronounced for wave V and inter-peak interval I-V, which in the 3rd group exceeds 4.4 ms, which, according to Thornton (1982), is a sign of brainstem lesions. The frequency of development of such changes in the brainstem increases as hearing decreases in persons with noise occupations, which confirms the unfavourable impact of industrial noise on the human body. At the same time, the first signs of noise influence on brain stem structures are manifested in some workers already with initial hearing impairment.

5. Conclusions

Thus, the conducted studies allow us to conclude that the impact of noise on a person is not limited to the damage of the peripheral part of the auditory analyser, but causes changes in its higher parts. Registration of CSVP in workers of noise occupations allows to obtain data on the state of the brainstem and thereby clarify the topics of the auditory analyser lesion under noise exposure, which is of theoretical and practical importance.