Noise Exposure and Hearing Impairment in Air Force Pilots.

OBJECTIVE: The goal of this study was to estimate noise exposure and hearing impairments in Swedish military pilots. It also aimed to analyze possible relations between noise exposure and hearing impairments.METHODS: The study group was an open cohort of 337 male pilots. They were longitudinally followed with pure tone audiograms every fifth year from the beginning of flight service until discharge. Outcome measures were prevalence of thresholds >20 dB HL and >40 dB HL at different ages, and incidence of impairments >20 dB HL, 30 dB HL, and 40 dB HL. Exposure variables were individual flight data and noise dose measurements. The ISO 1999 Database A was used for reference data.RESULTS: At 50 yr of age, 41% of the pilots were exposed to an equivalent noise dose exceeding the EU action level of Leq 80 dB(A). We observed significant elevated prevalence values of thresholds >20 dB HL in all age classes compared to the ISO 1999 Database A. These elevations were most pronounced at ages 30 and 40 yr and at 4 and 6 kHz in the left ear. Significantly elevated prevalence values of thresholds >40 dB HL compared to the ISO 1999 Database A were observed at age 40 and 50 yr at 4 and 6 kHz. In a Cox analysis we observed elevated hazard ratios of deteriorating thresholds with longer flight time/year in fast jet pilots.DISCUSSION: Military pilots had elevated prevalence values of hearing impairment. Of the subjects, 41% had been exposed to noise exceeding the EU risk limit. Increased flight time/year and flying fast jets were associated with elevated risk of hearing deterioration.Muhr P, Johnson A-C, Selander J, Svensson E, Rosenhall U. Noise exposure and hearing impairment in air force pilots. Aerosp Med Hum Perform. 2019; 90(9):757-763.

Treatment of military acoustic accidents with N-Acetyl-L-cysteine (NAC).

OBJECTIVE: To study if the antioxidant (AO) N-Acetyl-L-cysteine (NAC) reduces the risk of hearing loss after acoustic accidents in humans. DESIGN: A retrospective, observational study. STUDY SAMPLE: Personnel of the Swedish Armed Forces (SAF) exposed to military acoustic accidents during a 5 year period. Included in the study were 221 cases (mean age: 22.9 years). Most of the exposures, 84%, were weapon related. NAC (400 mg) was given directly after the accident in 146 cases; 75 had not received NAC. RESULTS: The prevalence of hearing thresholds ≥25 dB HL, and the incidence of threshold shifts ≥10 dB, was lower in the NAC group than in the non-NAC group directly after the noise exposure. The deterioration was temporary and not discernable a long time after the accident. The difference was most pronounced in the right ear. The risk reduction to get a temporary hearing loss (TTS), affecting one or both ears was 39% (significant) in the NAC group. CONCLUSIONS: The study has demonstrated a significant reduction of the incidence of TTS by the use of NAC. Since cases of both permanent hearing loss (PTS) and noise-induced tinnitus are recruited from cases with TTS, the demonstrated risk reduction indicates a positive effect of NAC.

Sensitivity and Specificity of Automated Audiometry in Subjects with Normal Hearing or Hearing Impairment.

OBJECTIVE: To investigate the sensitivity and specificity in an automatic computer-controlled audiometric set-up, used for screening purposes. DESIGN: Comparison between standardized audiometry and automated audiometry performed in the same participants. STUDY SAMPLE: In total, 100 participants (51 females and 49 males) were recruited to take part of this study the same day they visited the hearing clinic for clinical audiometry. Ages varied between 18 and 84 years (mean 45.9 in females, 52.3 in males). RESULTS: The participants were divided into groups, dependent of type of hearing. A total of 23 had normal hearing, 40 had sensorineural hearing loss, 19 had conductive hearing loss and 18 showed asymmetric hearing loss. The sensitivity for the automated audiometry was 86%-100% and the specificity 56%-100%. The group with conductive hearing loss showed the poorest sensitivity (86 %) and specificity (56 %). The group with sensorineural hearing loss showed the smallest variation in difference between the two methods. CONCLUSIONS: The results show that automated audiometry is a method suitable to screen for hearing loss. Screening levels need to be selected with respect to cause of screening and environmental factors. For patients with asymmetric hearing thresholds it is necessary to consider the effect of transcranial routing of signals.

Declining and fluctuating prevalence values of hearing impairment in 18-year old Swedish men during three decades.

OBJECTIVE: To analyze time trends in prevalence of hearing impairment in almost complete birth cohorts of 18-year old Swedish men from 1970s up to 2010. STUDY GROUPS: Before 1999, all 18-year old men, in Sweden, were called for a compulsory conscription examination. In 1971-1999, the participation rate in audiometry was 73-95%. After 1999, when exemption from conscription was allowed, the participation rate gradually declined to 52% in 2004. Samples with participation rates below 50% (2005-2010) were considered non-representative and excluded from the analyses. RESULTS: High-frequency hearing impairments (HFHI) 35-40 dB HL and ≥45 dB HL showed a decreasing trend over the observed period, from a prevalence of 2.9% (35-40 dB HL) and 3.8% (≥45 dB HL) respectively in 1971 to 1.4% and 1.1% respectively in 2004. HFHI 25-30 dB HL, showed slow variations over time and decreased from 8.5% in 1971 to 3.2% in 1981 followed by an increase to 10.4% in 1992. After that year there was a decrease to 5.2% in 2004. The slow fluctuations affected only HFHI 25-30 dB HL, mainly at 6 kHz. The left ear was more affected than the right ear. CONCLUSIONS: The most important observation was a decrease of HFHI 35-40 dB HL by 52% percent and of HFHI ≥45 dB HL by 71% between the years 1971 and 2004. The prevalence of HFHI 25-30 dB HL in young Swedish males fluctuated over a period of 33 years. Possible reasons for these trends and variations are discussed.

Influence of well-known risk factors for hearing loss in a longitudinal twin study.

OBJECTIVE: The aim was to investigate the influence of environmental exposures on hearing loss in a twin cohort. STUDY SAMPLE: Male twins born 1914-1958, representing an unscreened population, were tested for hearing loss at two occasions, 18 years apart. DESIGN: Clinical audiometry and a questionnaire were performed at both time points in this longitudinal study. Noise and solvent exposure were assessed using occupational work codes and a job exposure matrix. Hearing impairment was investigated using two different pure tone averages: PTA4 (0.5, 1, 2, and 4 kHz) and HPTA4 (3, 4, 6, and 8 kHz). RESULTS: Age affected all outcome measures. Noise exposure between time point one and two affected the threshold shifts of PTA4 and HPTA4 more in participants with a pre-existing hearing loss at time point one. Lifetime occupational noise exposure was a risk factor especially for the low-frequency hearing threshold PTA4. Firearm use was a statistically significant risk factor for all outcome measures. CONCLUSIONS: Pre-existing hearing loss can increase the risk of hearing impairment due to occupational noise exposure. An increased risk for NIHL was also seen in the group with exposures below 85 dB(A), a result that indicates awareness of NIHL should be raised even for those working in environments where sound levels are below 85 dB(A).

A demonstrated positive effect of a hearing conservation program in the Swedish armed forces.

OBJECTIVE: A revised hearing conservation program (HCP) was implemented in the Swedish Armed Forces in 2002. The aim of this study was to evaluate the incidence of significant threshold shifts (STS) in male conscripts heavily exposed to noise after the implementation of the new HCP, comparing the results to those of an earlier study from 1999/2000. DESIGN: The study was prospective and longitudinal, covering the period from reporting to military service to discharge. The outcome measure was the incidence of STS. Statistics from the military insurance system was analysed. STUDY SAMPLE: A total of 395 conscripts were included in the study (mean age 19 years). The control group (n: 839) consisted of men of the same age. RESULTS: In 2004/2005 the incidence rate of STS was 2.3% compared to 7.9% in 1999/2000 and compared to 3.7% among the controls. The number of cases of auditory complications reported from conscripts to the insurance system has decreased, from 16 to 5/100,000 days of military training, during the last decade. CONCLUSIONS: The new HCP apparently reduced the incidence rate of STS to one third compared to before the program was introduced and leveled it to the incidence rate in the control-group not exposed to military noise.

The influence of military service on auditory health and the efficacy of a Hearing Conservation Program.

The influence of military service on self-assessed hearing symptoms and measured auditory function was studied as well as the efficacy of the Hearing Conservation Program (HCP) of the Swedish Armed Forces. 839 conscripts were recruited for the study at reporting to military service. They were all exposed to noise over the risk-limits from weapons and vehicles and used earmuffs and/or earplugs. Questionnaires and pure tone screening audiometry were studied at the start and the end of the military service. Retrospective information regarding audiometry at conscription before military service was included as control. The prevalence values of tinnitus were 23% before and 32% after the service and of sensitivity to noise 16% and 19% respectively. The prevalence values of hearing impairment were 6.3% at conscription, 14.5% at reporting to military service, and 24% after the training period. The incidence values of hearing decline were 3.7% during the period with no military noise exposure and 6.6% during the military service. Acoustic accident increased the risk of worsened tinnitus and sensitivity to noise four times and for a high frequency hearing decline six times. We observed elevated prevalence values of tinnitus, sensitivity to noise and hearing impairment at discharge compared to before military service. We observed an elevated risk of hearing decline during military service. Acoustic accident increased the risk of tinnitus, noise sensitivity and hearing decline. We suggest improvements regarding inclusion criteria for military service, and for education regarding the HCP.

Self-assessed auditory symptoms, noise exposure, and measured auditory function among healthy young Swedish men.

The aim of the study was to estimate the prevalence of the exposure to ototraumatic factors and auditory symptoms, and to analyse the relations between these factors in a group of young healthy men. A total of 839 men, 19-22 years old, were recruited for the study when reporting for primary military service. A questionnaire was distributed and audiometry was performed. The prevalence of tinnitus, sensitivity to noise, and measured hearing impairment in the study group was 23.2%, 15.5%, and 14.5% respectively. Exposure to occupational noise often was reported by 21.4%, and playing loud music often by 16.5%. The young men who had experienced tinnitus after noise exposure had an elevated risk of high frequency hearing impairment, tinnitus, and sensitivity to noise. Those who played loud music had elevated prevalence values of tinnitus but not of hearing impairment. In this young group we observed high prevalence values of ototraumatic factors and auditory symptoms. We also observed significant correlations between tinnitus after noise exposure, self-assessed hearing symptoms, and hearing impairment.

Prevalence of hearing loss among 18-year-old Swedish men during the period 1971-1995.

AIMS: To study the hearing of 18-year-old men by using screening audiograms obtained at military conscription. METHODS: The study group comprised 301,873 Swedish men belonging to six age cohorts born from 1953 to 1977 who had been screened at age 18 years from 1971 to 1995. The prevalence of mild to moderate hearing loss was investigated. RESULTS: Of the entire study group, 13.1% had elevation of one or more pure tone thresholds. In most cases, 11.9%, the elevation was situated in the high-frequency region. High-frequency hearing loss was more common in the left ear (7.5%) than in the right ear (6.2%). The prevalence of hearing loss decreased during the period 1971 to 1981 from 15.7% to 8.3%. During the last part of the study period, 1986 to 1995, the prevalence increased from 9.8% to 16.3%. The increase included mild to moderate degrees of hearing loss with thresholds below 35 dB HL. The prevalence of threshold elevations was highest in sparsely populated areas of Sweden and lowest in large, metropolitan areas of Sweden from 1971 to 1986. During the last part of the study period the geographical differences decreased or disappeared. CONCLUSIONS: The total prevalence of hearing loss was in accordance with other reports. The frequency 6 kHz was most affected by threshold elevations. The prevalence of hearing loss decreased in the first part of the study period, and increased at the end of the study period. Hearing loss was most commonly seen in rural areas.

A study of hearing changes among military conscripts in the Swedish Army.

The aim of the study was to investigate the incidence and the relative risk of significant threshold shift (STS, >or=15 dB deterioration at any ear and audiometric frequency) during primary military service (7-9 months), and to investigate whether subjects with an initial slight hearing loss (thresholds>or=25 dB HL at any audiometric frequency and ear) were under increased risk. The investigation was made as a prospective audiometric study and included 747 men. An age-matched group of 138 individuals served as an unexposed control group, whose incidence of STS was 2.9%. In the exposed group the incidence was 7.9% and the relative risk 2.7 risk ratio (RR). In the subgroup of 95 persons, who already at reporting-for-training had a mild hearing loss, the incidence was 17%. The relative risk for STS in this group compared to the control group was 6.8 (RR), and compared to those with normal hearing at reporting was 3.1 (RR). In spite of hearing conservation efforts, hearing deterioration still occurs, above all in the artillery. Those who already at reporting-for-training had a mild hearing loss were at higher risk for STS compared to those with initially normal hearing.

Hearing loss in young men: possible aetiological factors.

In the present retrospective register study a very large data base consisting of screening audiograms obtained at military conscription of 18-year-old Swedish men was used. The study group comprised 450,175 men, aged 18 years, tested at conscription to military service. There were nine age groups covering a 24-year period, from 1971 to 1995. This database was compared with a number of different pre- and postnatal factors with possible influence on the hearing function. This ecologic methodology gives tentative clues (but no proof) of possible ototraumatic influences. The hearing capacity was fairly similar during the entire span of the study and only small variations were observed. There was a slight tendency of better hearing capacity in the later age groups, compared with the earlier ones. The mean thresholds of the frequencies 4 and 6 kHz were slightly elevated in 1971, 1976 and, to some extent also in 1992. We tried to calculate the levels of leisure noise exposure during the study period. There was no apparent tendency of reduced noise levels, on the contrary the noise levels seemed to increase. The treatment programmes for acute otitis media (AOM) underwent considerable changes during the period from the early fifties to the early eighties, when the participants were pre-school children. One possible explanation for the slight improvement of the hearing capacity could be less ototraumatic influence of AOM. Data about the occurrence of four common epidemic diseases, covering the periods preceding and succeeding the years when the participants were born indicated that influenza and possibly pertussis (whooping cough), constitute putative prenatal risk factors for mild to moderate high frequency hearing loss.

Fatigue after work in noise - an epidemiological survey study and three quasi-experimental field studies.

The contribution of noise exposure to fatigue at work was studied in a survey study and three field studies. The survey study was based on a questionnaire covering symptoms and work place exposure answered by 50 000 state employees. Noise exposure was also estimated from their type of job and self-rated noise exposure. Fatigue and headache were found to be more common among the noise exposed groups even after control for the effects of other critical variables. Study 2 compared reaction times before and after a week's work in high noise exposure and one in low exposure exposure in a group of aeroplane mechanics. Reaction times were prolonged after work in the noise week, whereas an opposite trend was seen in the control week. Study 3 showed a gradual increase of reaction times during a week of noise exposure in a group of aeroplane technicians. Study 4 compared reaction times and subjective fatigue among naval crews on a day with low and a day with high noise exposure. In one of the studied boat types the development of fatigue during the work day was accentuated on the day with high exposure.