Investigation of noise exposure effect on heart rate variability parameters.

This paper deals with the study of the effect of 135 min exposure to noise with intensity Leq 95 dB(A) in experimental conditions. Three experimental sessions: before, at the onset, and at the end of the noise exposure were conducted. The comparison of heart rate variability (HRV) parameters before and on the onset of the experiment showed tendency for significant decrease of the cardiointervals variability parameters: standard deviation (SD), sum of positive differences between successive cardiointervals (S), total wave energy in the cardiotachogram (S*Ns), mean difference between successive cardiointervals (V). Statistically significant increase of the mean value was found at HRV parameters related to the distribution of the cardiointervals: control adequacy parameter (IARP), equilibrium autonomic parameter (IVE), autonomous balance (IVB), homeostasis parameter (HI). At the end of the third experimental session HRV parameters were almost restored, but they did not achieve the initial values. An elevation of the sympathetic activity under noise exposure effect was found. In this aspect, the heart rate variability parameters were interpreted as a sensitive indicator for the quality of cardiac rhythm and they can be used for assessment of the functional status and the level of preserving of the adaptive reserves of the investigated persons.

Audiological problems in patients with tinnitus exposed to noise and vibrations.

Tinnitus is a hearing sensation appearing without available sound fluctuations in the external environment. It is one of the major, constant and earliest symptoms suggesting different pathology of the hearing analyser. It must be considered, though, that it is evidenced also at disturbed functions of other organs and systems of the organism. The aim of the present study is to elucidate the state of the hearing analyser in patients with tinnitus occupationally exposed to noise and vibrations in relation to therapy. The study was performed on 67 miners, aged 34-55, mean age 44.5 years. The workers with subjective tinnitus (29 persons--43% of the studied group) are the object of this investigation. They were subjected to the following tests of the hearing analyser: pure tone audiometry; above-threshold audiometry (Carhardt's adaptation test, Lusher's differential threshold, SISI test, Kietz test. The evidence reveals that the studied group of workers occupationally exposed to noise, vibrations, dust, toxic substances etc. complain predominantly of tinnitus. It is accompanied by vertigo, headache and disturbed balance. Changes in the hearing function are observed; manifested by different degree of hypacusia concerning air and bone conductivity in the pure tone audiometry. The above-threshold tests also evidence deviations suggesting disturbed hearing function. These changes can be explained by mechanical-toxic pathogenic mechanisms leading to cerebral and vestibular dysfunction most probably of vascular-circulatory type manifested by the above stated deviations. The results are the basis for the following conclusions: 1. The anamnestic profile of workers with tinnitus exposed to noise and vibrations shows a prevalent percentage of vertigo, followed by headache and disturbed balance. 2. The otoneurological profile shows changes in the air and bone conductivity manifested by different degree of hypacusia. 3. The evaluation of the above-threshold tests also confirms the evidence of disturbed hearing function. 4. The relevant therapeutical approach has to be elaborated, having in mind the existing suggestion about the mechanical-toxic etiopathogenesis of the developed process of vascular-circulatory type.

Disturbance of respiratory system in workers in smelter plants.

Workers from smelter plants are at high risk from lung injuries due to exposure to quartz sand, clay, resin, loams, airborne metals etc. The aim of this study was to investigate the relevance of the problem and the risk of occupational pathology in metallurgy at "ELMA" plant--Troyan. The study revealed decreased number of occupational lung diseases but the percentage rate (about 10%) of registered new cases with occupational lung diseases was maintained. No new cases with mixed silicosis were recorded. The results were compared to respective national data. Slowly evolving forms of diffusely outlined lung chart with late functional breathing disturbances were prevailing. Chronic bronchitis are presented as a polyetiologic paraoccupational disease.

Biological significance of the zoning of the masking effect of noise, related to the adaptive capacities of the auditory analyzer for speech communication.

The paper discusses the problem about the ergonomic assessment of the abilities of the auditory analyzer for processing of speech information, depending on the zoning of the masking effect of noise and the degree of speech communication. A significant increase of the loss of speech information with rise of the intensities of the masking effect of noise (from 21.33% at L eq. 40 dB up to 96% at L eq. 90 and less than 90 dB/A/) is found. The speech communication is graded into 4 bands, depending on the qualitative-quantitative criteria of the processed speech communication. The regularity of the standard for masking noise (L eq. 65 dB/A), which guarantees good comprehensibility is proved from the aspect of ensuring the necessary conditions for speech information perception. Equivalent levels of masking noise near or equal to L eq. 85 dB/A/ ensure satisfactory comprehensibility at the control boards. The abnormal intensities of the masking noise effect are of particular importance as they belong to the inadmissible (bad) zone of auditory perception of speech information.

Informativeness of critical ratios "useful signal-masking noise" in speech communication.

In experimental conditions the influence of 8 ratios "useful signal-masking noise" of 3 types of production noise (impulse, continuous and interrupted) is studied as well as continuous (white) noise as control on the perception of an audiometric test by 60 individuals with normal hearing. The test is understandable phonetically with difficulties and balanced at speech. The test intensity is L(equiv).70-75 dB/A/. The most expressed masking effect of continuous (white) noise, followed by the impulse and constant production noise is found. The lowest masking effect is found out at interrupted noise. This is explained by the acoustic characteristics of exposed types of noise. The masking effect of noise is limited to a high degree by the parameter "signal-noise" ratio, which is confirmed by the found negative correlation relationship with percentage speech intelligibility. The critical ratios "signal-noise", characterized with sharp decline of the level of discrimination of speaking signal and deterioration of the effectiveness of speech communication are established. In this paper the problem for conforming the speech communication both with the intensity and acoustic characteristics of masking noise and with the "signal-noise" ratio is discussed. Besides this in the critical "useful signal-masking noise" ratios better individual achievements could be a criterion for professional selection of candidates for operators.

Informativeness of the threshold adaptation and fatigue for assessment of the auditory health risk.

The management and control of modern automated productions evidence the elevated role of the auditory system as one of the distant sensor communication systems. The present study informs about the auditory adaptation and fatigue at the end of the working shift of 385 operators at control boards in "Kremikovtzi" State Company. The results of the monitoring of the dynamic changes show significant changes, expressed in aggravation of the auditory fatigue manifestation by moderate to significant disturbance of the adaptation-recovery processes. The analysis established a significant positive correlation between the changes in auditory fatigue and the duration of service. The frequencies of the speech range are preserved for a long time. The elevated auditory fatigue is observed in the injured hearing band 4,000 Hz, followed by 6,000 Hz and continuous dissemination to the middle frequencies of the speech band-2,000 and 1,000 Hz. The results of the study of the adaptation-recovery processes are characterised by statistically significant reliability, single direction and reproducibility and can be applied as informative criteria for assessment of the auditory health risk.

Assessment of the discomfort threshold of command board operators in automated productions with respect to its application in professional selection.

The discomfort threshold problem is not yet clear from the audiological point of view. Its significance for work physiology and hygiene is not enough clarified. This paper discussed the results of a study of the discomfort threshold, performed including 385 operators from the State Company "Kremikovtzi", divided into 4 groups (3 groups according to length of service and one control group). The most prominent changes were found in operators with increased tonal auditory threshold up to 45 and over 50 dB with high confidential probability. The observed changes are distributed in 3 groups: 1. increased tonal auditory threshold (up to 30 dB) without decrease of the discomfort threshold; 2. decreased discomfort threshold (with about 15-20 dB) at increased tonal auditory threshold (up to 45 dB); 3. decreased discomfort threshold at increased (over 50 dB) tonal auditory threshold. The auditory scope of the operators, belonging to groups III and IV (with the longest length of service) is narrowed, being distorted for the latter. This pathophysiological phenomenon can be explained by an enhanced effect of sound irritation and the presence of a recruitment phenomenon with possible engagement of the central part of the auditory analyzer. It is concluded that the discomfort threshold is a sensitive indicator for the state of the individual norms for speech-sound-noise discomfort. The comparison of the discomfort threshold with the hygienic standards and the noise levels at each particular working place can be used as a criterion for the professional selection for work in conditions of masking noise effect and its tolerance with respect to achieving the individual discomfort level depending on the intensity of the speech-sound-noise signals at a particular working place.