Sensory-neural hearing loss during combined noise and vibration exposure. An analysis of risk factors

Effect of noise and hand-transmitted vibration exposure on hearing and equilibrium under a simulated work environment with building tools

BACKGROUND

Construction workers are exposed to hand-transmitted vibration (HTV) and/or noise caused by vibrating hand tools in the work environment.

OBJECTIVE

The present study aims to investigate the effects of exposure to HTV and/or noise on workers' hearing loss and body balance.

METHODS

Forty construction workers were exposed to HTV (10 m/s2 rms, 31.5 Hz) and/or typical construction noise (90 dBA) in three simulated experiment scenarios with the vibrating hand-held tool for 30 minutes over three days. The hearing loss from 1000 to 6000 Hz and the body balance were determined before and after each exposure scenario.

RESULTS

Separate noise exposure at all frequencies except for 1000 Hz could significantly affect hearing threshold levels (p-value<0.05). Separate exposure to HTV cannot lead to a remarkable effect on hearing loss (p-value>0.05); however, it can synergistically increase the effect of noise on hearing loss. Also, the affected frequency range in concurrent exposure has been greater than in separate noise exposure. The separate effects of exposure to HTV and noise on the subjects' body balance were not statistically significant (p-value>0.05); however, these effects became significant in concurrent exposure (p-value<0.05). Based on the estimated effect sizes, noise could synergistically increase the observed effect of HTV on body balance.

CONCLUSION

There is a synergistic interaction between HTV and noise on hearing loss and body balance. It seems necessary to pay attention to the risk evaluation of simultaneous exposure to noise and HTV when setting the occupational action limit values.

Thunder and lightning-a report on firework-associated acoustic trauma at New Year 2021/2022

BACKGROUND

This cross-sectional study aimed to assess the frequency and type of firework-associated acoustic trauma occurring in Germany on New Year's Eve 2021, despite the ban on firework sales due to the COVID-19 pandemic.

MATERIALS AND METHODS

The survey period lasted 7 days, from 28 December 2021 to 03 January 2022. A questionnaire inquired date, type and treatment of trauma, sex, and age of the patient, and whether the trauma occurred when lighting or watching fireworks. Hearing impairment was classified according to the World Health Organization (WHO grades 0 to 4), and concomitant tinnitus, vertigo, or other injuries were recorded. The questionnaire was sent to the otorhinolaryngology departments of 171 hospitals in Germany.

RESULTS

Of 37 otorhinolaryngology departments, 16 reported no and 21 reported 50 patients with firework-associated acoustic trauma. Mean age was 29 ± 16 years and 41 of 50 patients were males. Of these 50 patients, 22 presented without and 28 with hearing loss, 32 reported tinnitus and 3 vertigo; 20 patients were injured when lighting fireworks and 30 when watching. Hearing impairment was classified as 14 × WHO grade 0, 5 × WHO grade 1, 4 × WHO grade 2, 2 × WHO grade 3, and 3 × WHO grade 4. Inpatient treatment was received by 8 patients and 11 suffered from concomitant burn injuries.

CONCLUSION

Despite the sales ban, some firework-associated acoustic traumas occurred at New Year 2021/2022 in Germany. Some instances led to hospitalization, but an even higher number of unreported cases can be assumed. This study can serve as a baseline for further annual surveys to raise the awareness of the danger of seemingly harmless fireworks for the individual.

The Combined Impact of Hand-Arm Vibration and Noise Exposure on Hearing Sensitivity of Agricultural/Forestry Workers-A Systematic Literature Review

Hand-arm vibration (HAV), which potentially causes vibration white finger (VWF), and occupational noise are serious issues in the agricultural and forestry industries. Generally, agricultural workers operate as single-family/small businesses and thus are exempted from Occupational Safety and Health Administration (OSHA) regulations/laws for noise and HAV otherwise applicable to other industries in general. The agricultural/forestry sectors are at increased risk as working hours are longer than a typical 8-h work shift putting them at greater risk of hearing loss. The study was conducted to assess the possible association between hearing sensitivity on combined exposure to noise and hand-arm vibration. A systematic literature review was conducted on exposure to noise and HAV in the agricultural/forestry sector and the resulting impacts on hearing. The peer-reviewed articles in English were searched with 14 search words in three databases of PubMed, Ergo Abstracts, and Web of Science without any filter for the year for fully available article text. The database literature search resulted in 72 articles. Forty-seven (47) articles met the search criteria based on the title. Abstracts were then reviewed for any relationship between hearing loss and hand-arm vibration/Raynaud's phenomenon/VWF. This left 18 articles. It was found that most agricultural workers and chainsaw workers are exposed to noise and VWF. Hearing is impacted by both noise and aging. The workers exposed to HAV and noise had greater hearing loss than non-exposed workers, possibly due to the additive effect on temporary threshold shift (TTS). It was found that VWF might be associated with vasospasm in the cochlea through autonomous vascular reflexes, digital arteries narrowing, vasoconstriction in the inner ear by noise, ischemic damage to the hair cells and increased oxygen demand, which significantly affects the correlation between VWF and hearing loss.

[Thunder and lightning-a report on firework-associated acoustic trauma at New Year 2021/2022 (German version)]

BACKGROUND

This cross-sectional study aimed to assess the frequency and type of firework-associated acoustic trauma occurring in Germany on New Year's Eve 2021, despite the ban on firework sales due to the COVID-19 pandemic.

MATERIALS AND METHODS

The survey period lasted 7 days, from 28 December 2021 to 03 January 2022. A questionnaire inquired date, type and treatment of trauma, sex, and age of the patient, and whether the trauma occurred when lighting or watching fireworks. Hearing impairment was classified according to the World Health Organization (WHO grades 0 to 4), and concomitant tinnitus, vertigo, or other injuries were recorded. The questionnaire was sent to the otorhinolaryngology departments of 171 hospitals in Germany.

RESULTS

Of 37 otorhinolaryngology departments, 16 reported no and 21 reported 50 patients with firework-associated acoustic trauma. Mean age was 29 ± 16 years and 41 of 50 patients were males. Of these 50 patients, 22 presented without and 28 with hearing loss, 32 reported tinnitus and 3 vertigo; 20 patients were injured when lighting fireworks and 30 when watching. Hearing impairment was classified as 14 × WHO grade 0, 5 × WHO grade 1, 4 × WHO grade 2, 2 × WHO grade 3, and 3 × WHO grade 4. Inpatient treatment was received by 8 patients and 11 suffered from concomitant burn injuries.

CONCLUSION

Despite the sales ban, some firework-associated acoustic traumas occurred at New Year 2021/2022 in Germany. Some instances led to hospitalization, but an even higher number of unreported cases can be assumed. This study can serve as a baseline for further annual surveys to raise the awareness of the danger of seemingly harmless fireworks for the individual.

Hearing Loss and Associated Factors Among Noise-Exposed Workers in Palm Oil Mills

Introduction

Almost 90% of the reported occupational diseases in Sabah, Malaysian Borneo were due to hearing loss. The manufacturing industry was the main contributor to this problem. This study aims to identify the prevalence and associated factors for hearing loss among workers in the palm oil manufacturing industry in Sabah.

Material and Methods

A cross-sectional study was done among 312 respondents from five palm oil mills in Sabah from January to April 2019. Audiometric tests, validated questionnaires and sound level meters were used. Chi-square test and independent t-test were conducted to determine the associated factors for hearing loss.

Results

75% (n = 234) of the respondents were diagnosed with hearing loss. Most of them were male (96.2%) with a mean age of 44.4 (SD 9.8) years, mean duration of employment of 16.2 (SD 9.7) years and mean noise exposure of 96.1 (SD 4.8) dB(A). The significant factors associated with hearing loss were older age (p = 0.001), married (p = 0.001), blue-collar jobs (p = 0.003), smoking (p = 0.001), works with noisy machinery (p = 0.005), lower level of noise exposed (p = 0.015), longer duration of employment (p = 0.001), and longer overtime hours per week (p = 0.001).

Conclusion

The prevalence of hearing loss among workers in the noise-exposed palm oil industries was high. Annual audiometry testing and job rotation from noise-exposed workstations were recommended. A smoking cessation program may help but reduction of noise from the source by engineering control is still the best method.

The Association Between Occupational Exposure to Hand-Arm Vibration and Hearing Loss: A Systematic Literature Review

Background

Hearing loss is one of the most prevalent worker health conditions worldwide. Although the effect of noise exposure on hearing is well researched, other workplace exposures may account for significant hearing loss. The aim of this review was to determine whether occupational hand–arm vibration exposure through use of power or pneumatic tools, independent of noise exposure, is associated with permanent hearing loss. Do workers suffer from hand–arm vibration–induced hearing loss?

Methods

Peer-reviewed articles published in English between 1981 and 2020 were identified through five online databases with five search keywords. Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines, including online database search methodology, study selection, article exclusion, and assessment of potential study design confounders and biases, were followed.

Results

Database searches retrieved 697 articles. Fifteen articles that reported 17 studies met the criteria for review. All but two studies revealed statistically significant associations between occupational exposure to hand–arm vibration and hearing loss. The majority of the study results revealed associations between hand–arm vibration and hearing loss, independent of potential age and noise confounders.

Conclusion

Few studies have examined the association between occupational exposure to hand–arm vibration and hearing loss. Dose response data were limited as only one study measured vibration intensity and duration. Although the majority of studies identified statistically significant associations, causal relationships could not be determined. Further research using standardized and uniform measurement protocols is needed to confirm whether the association between occupational exposure to hand–arm vibration and permanent hearing loss is causal and the mechanism(s).

Comparative assessment of shift in hearing threshold among handicraft operatives in India

This case-control exploratory study is first of its kind to assess the noise exposure and loss in hearing threshold (HT) due to the occupational use of hand tools used for handicraft work. Sixty male participants involved in different crafts trade and a reference group of 50 office workers were selected. The sound pressure levels under actual work conditions were measured as per the method outlined in IS 7194:1994. The mean equivalent sound pressure level was quite high (96.37 dB(A)), exceeding the exposure limit of 90 dB(A). Audiometric tests were conducted to compare the HT between both the groups. In agreement with dose consumed, the exposed workers exhibit moderate hearing impairment in the frequency range of 1500-6000 Hz. The association of HT at different frequencies among occupation were detected using post-hoc multiple comparisons. 95% of the workers showed hearing handicap at some level and noise-induced hearing loss increases with higher age and experience. Interventions in the hand tools, implementation of hearing conservation programmes and practice of personal protective equipments have been suggested. Practitioner Summary: As the primary outcomes, comparative assessment of the shift in hearing threshold was analyzed in anticipation to develop a better work system. Results from the study report that the sound pressure level was fairly high and 95% of the handicraft operatives showed hearing handicap at some level.

Hearing impairment and contributing factors among fertilizer factory workers

Introduction:

Hearing impairment remains the main occupational health problem in the manufacturing industry, and its contributing factors have not been well controlled.

Methods:

Unmatched case control and comparative studies were carried out among fertilizer factory workers in Sarawak with the aim of determining contributing factors for hearing impairment. Respondents consisted of 49 cases that were diagnosed from 2005 to 2008 with 98 controls from the same work places. Chi-square test and Mann-Whitney test were used in a univariate analysis to determine the association between hearing impairment and the contributing risks being studied.

Results:

The results of the univariate analysis showed that hearing impairment was significantly (p<0.05) associated with older age, lower education level, high smoking dose, high occupational daily noise dose, longer duration of service, infrequent used of hearing protection device (HPD), and low perception of sound on HPD usage. Multivariate logistic regression of hearing impairment after controlling for age found the following five variables: occupational daily noise dose ≥50% (OR 3.48, 95% CI 1.36-8.89), ≥15 years of services (OR 2.92, 95% CI 1.16-7.33), infrequent use of HPD (OR 2.79, 95% CI 1.15-6.77), low perception of sound on HPD (POR 2.77, 95% CI 1.09-6.97), and smoking more than 20 packs per year (OR 4.71, 95% CI 1.13-19.68).

Discussion:

In conclusion, high occupational noise exposure level, longer duration of service, low perception of sound on HPD, infrequent used of HPD, and smoking more than 20 packs per year were the contributing factors to hearing impairment, and appropriate intervention measures should be proposed and taken into considerations.

Occupational noise exposure and hearing: a systematic review

Purpose

To give a systematic review of the development of noise-induced hearing loss (NIHL) in working life.

Methods

A literature search in MEDLINE, Embase, Web of Science, Scopus, and Health and Safety Abstracts, with appropriate keywords on noise in the workplace and health, revealed 22,413 articles which were screened by six researchers. A total of 698 articles were reviewed in full text and scored with a checklist, and 187 articles were found to be relevant and of sufficient quality for further analysis.

Results

Occupational noise exposure causes between 7 and 21 % of the hearing loss among workers, lowest in the industrialized countries, where the incidence is going down, and highest in the developing countries. It is difficult to distinguish between NIHL and age-related hearing loss at an individual level. Most of the hearing loss is age related. Men lose hearing more than women do. Heredity also plays a part. Socioeconomic position, ethnicity and other factors, such as smoking, high blood pressure, diabetes, vibration and chemical substances, may also affect hearing. The use of firearms may be harmful to hearing, whereas most other sources of leisure-time noise seem to be less important. Impulse noise seems to be more deleterious to hearing than continuous noise. Occupational groups at high risk of NIHL are the military, construction workers, agriculture and others with high noise exposure.

Conclusion

The prevalence of NIHL is declining in most industrialized countries, probably due to preventive measures. Hearing loss is mainly related to increasing age.

Electronic supplementary material

The online version of this article (doi:10.1007/s00420-015-1083-5) contains supplementary material, which is available to authorized users.

Risk of hearing loss among workers with vibration-induced white fingers

BACKGROUND

We examined the risk of hearing loss for workers who use hand-held vibrating tools with vibration-induced white fingers (VWF) compared to workers without VWF.

METHODS

Data on 184 participants from a 21-year cohort were gathered with questionnaires and measurements. The effects on hearing status of VWF, hand-arm vibration exposure, smoking habits, age and two-way interactions of these independent variables were examined with binary logistic regression. Analyses were made for the right hand and ear as well as for the hand with VWF and the ear with worse categorized hearing status.

RESULTS

Workers with VWF in their right hand had an increased risk of hearing loss (odds ratio 2.2-2.3) in the right ear. Workers with VWF in any hand did not have any increased risk of hearing loss in the ear with worse hearing status.

CONCLUSIONS

This study supports the hypothesis that VWF increases the risk of hearing loss among workers who use hand-held vibrating tools in a noisy environment.

Hearing profile of brazilian forestry workers' noise exposure

Introduction Researchers studying the hearing health of forestry workers have revealed the presence of a noise-induced hearing loss (NIHL) in this population and have concluded that the vibration of the equipment, the carbon monoxide released by motors, and pesticides might also contribute to NIHL.

Objective To analyze the noise exposure in the Brazilian forestry industry workers and the effects on hearing.

Methods The study sample comprised 109 employees of a company that specialized in reforestation. Their participants' mean age was 35.5 years (21 to 54 years), mean tenure at the company was 3.9 years (1 to 13 years), and mean total duration of noise exposure was 12.3 years (1 to 30 years). The existing documentation reporting on the jobs risk analysis was examined, noise level was measured, and pure tone audiometry was performed in all participants. Participants were divided into three groups according to their noise exposure levels in their current job.

Results Of the participants who were exposed to noise levels less than 85 dBA (decibels with A-weighting filter), 23.8% had hearing loss, and 5.5% of the participants who were exposed to noise ranging from 85 to 89.9 dBA and 11% of the participants who were exposed to noise greater than 90 dBA had audiogram results suggestive of NIHL.

Conclusion The implementation of a hearing loss prevention program tailored to forestry workers is needed.

Cochlear damages caused by vibration exposure

Background

Many industrial devices have an excessive vibration which can affect human body systems. The effect of vibration on cochlear histology has been as a debatable problem in occupational health and medicine.

Objectives

Due to limitation present in human studies, the research was conducted to survey the influence of vibration on cochlear histology in an animal model.

Materials and Methods

Twelve albino rabbits were experimented as: Vibration group (n = 6; exposed to 1.0 m.s^-2 r.m.s vertical whole-body vibration at 4 - 8 Hz for 8 hours per day during 5 consecutive days) versus Control group (n = 6; the same rabbits without vibration exposure). After finishing the exposure scenario, all rabbits were killed by CO₂ inhalation; their cochleae were extracted and fixed in 10% formaldehyde for 48 hours, decalcified by 10% nitric acid for 24 hours. Specimens were dehydrated, embedded, sectioned 5 µm thick and stained with Hematoxylin and Eosin for light microscopy observations.

Results

Severely hydropic degenerated and vacuolated inner hair cells (IHCs) were observed in vibration group compared to the control group. Inter and intracellular edema was appeared in supporting cells (SC). Nuclei of outer hair cells (OHCs) seemed to be pyknotic. Slightly thickened basilar membrane (BM) was probably implied to inter cellular edematous. Tectorial Membrane (TM) was not affected pathologically.

Conclusions

Whole-body vibration could cause cochlear damages in male rabbits, though vibration-induced auditory functional effects might be resulted as subsequent outcome of prolonged high level vibration exposures.

Assessment of the influence of whole body vibration on Cochlear function

Background

Whole body vibration (WBV) is a potentially harmful consequence resulting from the dissipation of energy by industrial machineries. The result of WBV exposure on the auditory system remains unknown. The objective of the present research was to evaluate the influence of WBV on cochlear function, in particular outer hair cell function. It is hypothesized that WBV impairs cochlear function resulting in decreased Distortion Product Otoacoustic Emission (DPOAE) levels (L_dp) in rabbits subjected to WBV.

Methods

Twelve rabbits were equally divided into vibration and control groups. Animals in vibration group were exposed to 1.0 ms^-2 r.m.s vertical WBV at 4–8 Hz for 8 h/day during 5 consecutive days. Outer hair cell function was assessed by comparing repeated-measurements of DPOAE levels (L_dp) across a range of f₂ frequencies in rabbits both exposed and unexposed to WBV. DPOAE level shifts (LS_dp) were compared across ears, frequencies, groups, and times.

Results

No differences were seen over time in DPOAE levels in the non-exposed rabbits (p = 0.082). Post-exposure L_dp in rabbits exposed to WBV were significantly increased at all test frequencies in both ears compared to baseline measures (p = 0.021). The greatest increase in L_dp following exposure was seen at 5888.5 Hz (mean shift = 13.25 dB). Post-exposure L_dp in rabbits exposed to WBV were not significantly different between the right and left ears (p = 0.083).

Conclusion

WBV impairs cochlear function resulting in increased DPOAE responses in rabbits exposed to WBV. DPOAE level shifts occurred over a wide range of frequencies following prolonged WBV in rabbits.

Effects of whole body vibration on outer hair cells' hearing response to distortion product otoacoustic emissions

Whole body vibration (WBV) is one of the most vexing problems in industries. There is a debate about the effect of WBV exposure on hearing system as vibration-induced hearing loss. The purpose of this study was to investigate outer hair cells' (OHCs') hearing response hearing response to distortion product otoacoustic emissions (DPOAEs) in rabbits exposed to WBV. It was hypothesized that the DPOAE response amplitudes (A(dp)) in rabbits exposed to WBV would be lower than those in control rabbits not exposed to WBV. New Zealand white (NZW) rabbits as vibration group (n = 6, exposed to WBV in the z-axis at 4-8 Hz and 1.0 ms(-2) root mean square for 8 h per day during five consecutive days) and NZW rabbits as control group (n = 6, not exposed to any WBV) were participated. A(dp) and noise floor levels (L(nf)) were examined on three occasions: day 0 (i.e., baseline), day 8 (i.e., immediately 1 h after exposure), and day 11 (i.e., 72 h following exposure) with f(2) frequencies ranging from 500 to 10,000 Hz and primaries L(1) and L(2) levels of 65 and 55 dB sound pressure level, respectively. Main effects were statistically found to be significant for group, time, and frequency (p < 0.05). DPOAE amplitudes were significantly larger for rabbits exposed to WBV, larger on day 8 and larger for mid to high f(2) frequencies (at and above 5,888.50 Hz). Main effects were not statistically found to be significant for ear (p > 0.05). Also, four statistically significant interactions including time by ear, time by frequency, group by frequency, and group by time were detected (p < 0.05). Contrary to the main hypothesis, DPOAE amplitudes were significantly larger for rabbits exposed to WBV. WBV exposure significantly led to enhanced mean A(dp) at mid to high frequencies rather than at low ones.

Noise-induced hearing loss in construction workers being assessed for hand-arm vibration syndrome

BACKGROUND

Construction workers are at risk of noise-induced hearing loss (NIHL) but often have no periodic audiometric testing.

METHODS

The participants were construction workers assessed for Hand-Arm Vibration Syndrome (HAVS) at the Occupational Health Clinic, St. Michael's Hospital, Toronto, Ontario. Audiometry was offered and 169 of the 191 workers assessed for HAVS agreed to have the audiometric test. The objective was to examine the prevalence of hearing loss in these 169 workers and to determine the effect on hearing of duration of work in construction (as a proxy for noise exposure) and the severity of vibration white finger (VWF) which previous studies have suggested is a marker for increased individual susceptibility for NIHL. VWF was measured by the Stockholm vascular scale.

RESULTS

All participants were men, median age of 57 (range: 28-75), median number of years worked in construction of 35 (range: 4-52). All of the Spearman rank correlations between years worked in construction and the hearing levels at each audiometric frequency were statistically significant (p < 0.001). Overall, 31 (18.3%) participants had hearing loss at or above the level at which a workers' compensation pension would be granted in Ontario and the prevalence of this auditory outcome had a statistically significant increase as years worked in construction increased. Multivariate linear regression indicated that VWF also had a statistically significant effect on hearing loss for all audiometric frequencies combined after controlling for years worked in construction.

CONCLUSION

Improved prevention of hearing loss in construction workers is needed.

Smoking and height as risk factors for prevalence and 5-year incidence of hearing loss. A questionnaire-based follow-up study of employees in Denmark aged 18–59 years exposed and unexposed to noise

This paper investigated whether smoking and short stature in adulthood were independent risk factors for hearing loss. We reanalyzed data from the Danish Work Environment Cohort Study (an existing cohort study), on prevalence of self-reported hearing loss among 7,221 employees and on five-year incidence among 4,610 employees. We found that smoking predicted hearing loss incidence and prevalence. Smoking did not predict incidence at noise exposure during half or more of a worker's hours. Very short stature predicted prevalence in the total adult population only weakly, but strongly among employees born before 1951. These prospective findings indicate that smoking is an independent risk factor for incidence of hearing loss. Very short stature predicted prevalence of hearing loss only in a subpopulation.

The association between short stature and sensorineural hearing loss

In order to test the Thrifty Phenotype Hypothesis on hearing, data from two cross-sectional studies on hearing were re-evaluated. The data sets comprised 500 18-year-old conscripts, and 483 noise-exposed male employees. Sensorineural hearing loss (SNHL) was over-represented among conscripts with a short stature (odds ratio=2.2) or hearing loss in the family (odds ration=4.2), but not among noise-exposed conscripts (odds ratio=0.9-1.3). Among noise-exposed short employees, hypertension and age exhibited a negative impact on high frequency hearing thresholds, while among tall employees hypertension had no effect on hearing and the influence of age was less pronounced (p<0.01 for body height; p<0.02 for age, hypertension and the interaction between body height and hypertension; p<0.05 for the interaction between body height and age). This suggests that mechanisms linked to fetal programming and growth retardation and/or insulin-like growth factor 1 levels during fetal life, such as a delayed cell cycle during the time window when the cochlea develops, may cause SNHL in adulthood.

Experimental vibratory damage of the inner ear

The aim of the experiment was to determine the effect of whole-body vibration on the inner ear. The investigations were carried out on 40 guinea pigs, subjected to sinusoidal vibration (10 Hz/5 mm/1.4 g rms) for 1 to 6 months in a noiseless apparatus. Cochlear microphonic measurements were done with a phase-sensitive detection technique for the levels 70, 80 and 90 dB and the frequencies of 0.26, 0.5, 1 and 2 kHz from the apex of the cochlea and for 4 and 8 kHz from the region of the round window. Analysis of 1,440 measurements suggested the possibility of damage appearing in the upper turnings of the cochlea. The subsequent morphological analysis was based on the estimation of the state of the hair cells (a three-degree scale of injury) in a Zeiss DSM 950 scanning microscope and of the structure of the fibers of the acoustic nerve in a Zeiss EM 900 transmission microscope. Vibration-induced changes were seen in all the examined inner ears of the experimental groups. Hair-cell damage was more often seen in the region of the apex, spreading gradually in the direction of the base and from the circumference (outer hair cells of the third row) to the modiolus. The most characteristic vibrational changes of the acoustic nerve fibers occurred in 100% of the examined myelin sheaths and were visible as decreases in their electrodensity. The changes in both the assessed elements of the inner ear appeared simultaneously but independently and were directly connected with the duration of the experiment. The results obtained allow an explanation of the mechanism of hearing loss in persons subjected to whole-body vibration. The damages done to the inner ear structures may cause a worsening of hearing there, especially in the low and medium frequencies.

A prospective case-controlled study of patients presenting with idiopathic sensorineural hearing loss to examine the relationship between hyperlipidaemia and sensorineural hearing loss

The prevalence of hyperlipidaemia in the normal population means that hyperlipidaemia is often found in patients who have a hearing loss of unknown aetiology. We prospectively undertook a case-controlled study of 85 patients presenting consecutively with a sensorineural hearing loss of unknown aetiology to see if the prevalence of hyperlipidaemia differed between the group with an idiopathic sensorineural hearing loss and a control population. Control subjects were recruited from patients undergoing nasal surgery for structural abnormalities. Both the study and control groups were also compared with the National Study of Hearing data. Hyperlipidaemia was no more prevalent in a population with idiopathic sensorineural hearing loss than a control population. No consistent association between hyperlipidaemia and hearing loss was found.

Multiplicative effect of smoking and age on hearing impairment

PURPOSE

To determine the combined effect of smoking and age on hearing impairment.

MATERIALS AND METHODS

Pure tone audiometry test was conducted on 263 residents of a rural village who were not exposed to noise. The pack-years of smoking were computed from the subjects' smoking history. The association between pack-years and hearing impairment was assessed. The combined effect of smoking and age on hearing impairment was determined based on prevalence rate ratio.

RESULTS

There was a statistically significant trend in the number of pack-years of smoking and age as risk factors for hearing impairment. The prevalence rates of hearing impairment for nonsmokers aged 40 years and younger, smokers aged 40 years and younger, nonsmokers older than 40 years of age, and smokers older than 40 years of age were 6.9%, 11.9%, 29.7%, and 51.3%, respectively. The prevalence rate ratio for nonsmokers aged 40 years and younger, smokers aged 40 years and younger, nonsmokers older than 40 years of age, and smokers older than 40 years of age (nonsmokers aged 40 years and younger as a reference group) was 1, 1.7, 4.3, and 7.5, respectively. The prevalence rate ratios showed a multiplicative effect of smoking and age on hearing impairment.

CONCLUSION

Age and smoking are risk factors for hearing impairment. It is clear that smoking and age have multiplicative adverse effects on hearing impairment.

Hearing loss risk from exposure to shooting impulses in workers exposed to occupational noise

The effect of shooting impulses on hearing was analysed in 150 professional forest workers exposed to noise from chain saws. The exposure to shooting impulses (Lesi) was designed to take into account the peak levels of shooting impulses, their number and use of hearing protectors. Hearing loss was dependent on Lesi even after allowing for the age of subjects and their exposure to chain saw noise. Hearing threshold levels were compared between pairwise matched groups with high and low Lesi. Proper matching was achieved for age, chain saw noise, salicylate consumption, blood pressure, cholesterol, smoking and vibration-induced white finger symptoms. The workers with high Lesi had 9 dB greater hearing loss at 4 kHz and 10 dB greater hearing loss at 8 kHz than those with low Lesi, the difference being significant at P < 0.05 level. In evaluation of noise-induced hearing loss the exposure to shooting impulses from different calibre weapons should be determined since they increase the extent of hearing loss. The present study describes the Lesi method which more accurately evaluates the harmful effects of shooting noise impulses on hearing.

Heat, cold, noise, and vibration

Exposure to a cold environment induces a number of physiological alterations, the most serious being hypothermia. This state can occur in all individuals, but the very young and the elderly are more susceptible. Environmental and industrially generated high ambient temperature can place further stress on aged individuals and workers, resulting in a complex symptom picture. Morbidity and death may result from such exposures. Causative factors have been identified. Noise exposure induces hearing losses above those secondary to the aging process. Psychophysiological effects during noise exposure are considered to result from the sympathetic activity secondary to a general stress reaction. Vibration from the use of power tools results in Raynaud's phenomenon. However, modification of power tools has reduced the symptoms associated with vibration exposure. Termination of exposure to vibration appears eventually to reduce symptoms related to white-finger spasms. Interaction between these stressors has not been clarified because of the complex effects of each. The need for additional information about the response to these stressors is evident.

The quest for interaction: studies on combined exposure

A literature review was performed on the subject of combined exposure to stressors in the working situation. A general, dynamic model of workload served as the theoretical framework for the study. In this model, every factor that triggers a physiological or psychological response in the worker is regarded as a stressor. Decision latitude plays an important role in the model. A quantitative and qualitative analysis was performed on the available literature. It was concluded that the stressors that appear in studies on combined exposure stem mostly from the physical, chemical and biological environment. The task contents, the labor conditions, social relationships at work and the decision latitude are considerably less often studied in relation to combined exposure. It is concluded that important concepts in the study of combined exposure (e.g. interaction, independence, synergism, antagonism) are often quite carelessly mentioned in the literature. Explicit definition of these concepts is lacking in many publications. Establishment of maximum exposure levels is not yet possible for most stressor combinations. Examples are given of combinations that do allow more or less definite conclusions. It is recommended that more studies should be interdisciplinary organized. More studies are necessary in the field, studying effects of long exposure periods in the working population instead of studying students in laboratory situations. Exposure of susceptible groups, such as older workers and partially disabled workers, deserves special attention.

Risk factors in the genesis of sensorineural hearing loss in Finnish forestry workers

A detailed analysis of risk factors for the development of sensorineural hearing loss (SNHL) was carried out in 199 forest workers. The hearing threshold of both ears at 4000 Hz was measured, and the effect of age, exposure to noise, blood pressure, presence of vibration induced white finger (VWF), tobacco smoking, plasma LDL-cholesterol concentration, and consumption of drugs were evaluated by multiple linear regression analysis. Aging was the major risk factor, followed by exposure to occupational noise and the presence of VWF. Plasma LDL-cholesterol concentration and the use of antihypertensive drugs also correlated significantly with SNHL. These main factors were able to explain about 28% of the SNHL variance. Additional factors in the analysis, including smoking, systolic and diastolic blood pressure, and consumption of salicylates did not significantly contribute to the genesis of SNHL.

Evaluation of factors affecting sensory neural hearing loss

A detailed analysis of risk factors in the development of sensory-neural hearing loss (SNHL) was carried out in 199 forest workers. The mean hearing threshold of both ears at 4000 Hz was measured and the effect of age, exposure, blood pressure, presence of vibration induced white finger (VWF), tobacco smoking and plasma lipid concentrations on SNHL were evaluated by multiple linear regression analysis. A part of aging the major risk factors were presence of VWF, elevation of LDL-cholesterol level and usage of antihypertensive agents. Additional factors in the analysis, e.g. smoking and diastolic and systolic blood pressure did not significantly contribute to the genesis of SNHL.