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.
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.
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.
To investigate the sensitivity and specificity in an automatic computer-controlled audiometric set-up, used for screening purposes.Comparison between standardized audiometry and automated audiometry performed in the same participants.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).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.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.
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.
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).
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 in1992. 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.
During compulsory military service, the hearing capacity of the conscripts is at risk, because of exposure to excessive continuous and impulse noise. In young adult life, a multitude of other risk factors also might result in auditory symptoms and hearing impairment. A Military Hearing Conservation Program is of the utmost importance to prevent auditory complications caused by the military noise exposure. Aims: To assess the prevalence values of hearing impairment in young men at conscription in the period 1971-1995. To analyse relations between causative factors and hearing symptoms/hearing impairment before military service. To estimate the incidence and relative risk of hearing decline during military service (the efficacy of the Hearing Conservation Program). Methods: In Paper I we obtained cross-sectional data on prevalence values of hearing impairment at conscription, at age 18, from six complete age cohorts born in 19531977, in all 337 986 men. Of these, 89.3% were tested with screening audiometry. In Paper III, a group of 747 conscripts from three regiments performed mandatory screening audiometry at reporting to training in 1999 and at discharge in 2000. In Paper II and IV, a group of 839 men from three other military units performed mandatory screening audiometry, and filled in a questionnaire at reporting to training in 20022004. The same procedure was repeated at discharge. In Paper II, III, and IV the cross sectional data were evaluated as prevalence values and the longitudinal data as incidence values. The comparison groups with no military noise exposure made the first audiometric test at the Centre of Conscription and the second at the army unit at reporting for training. Results: The prevalence values of hearing impairment decreased in the period 19711981 from 15.7% to 8.3% and increased in 1986-1995 from 9.8% to 16.3%. This pattern was caused by changes of mild high frequency elevations. The threshold elevations of 45 dB HL or more decreased over the entire study period. Most often only one ear was affected. High frequency hearing impairment was more common in the left ear. Before military service 6.8% of the conscripts reported one or more auditory symptoms often or always. The most common noise exposure was rock concerts or discotheques. TTS after noise exposure was related to elevated prevalence values of hearing impairment and auditory symptoms. Playing loud music was related to an elevated risk for tinnitus but not for hearing impairment. Prevalence values of hearing impairment, tinnitus and sensitivity to noise were elevated at discharge compared to at reporting to service. At discharge from military service we observed a relative risk of hearing decline of 2.7 in 2000 and of 1.8 in 2003-05. In 2000 we observed an elevated risk of hearing decline during military service for those of the conscripts who had a mild hearing impairment already at reporting to training. This effect was not observed in the more strictly screened group in 2003-2005. Conclusions: High prevalence values of hearing impairment and auditory symptoms were observed before military service. These impairments were related to different causative factors. Elevated relative risk of hearing decline during military service was observed. LIST OF PUBLICATIONS I. Muhr P, Rasmussen R, Rosenhall U: Prevalence of hearing loss among 18year-old Swedish men during the period 1971-1995, Scand J Public Health 2007; 35:524-532. II. Muhr P, Rosenhall U: Self-assessed Auditory Symptoms, Noise Exposure and Measured Auditory Function among healthy young Swedish Men, Int J Audiology, 2010; 49:317-325. III. Muhr P, Mansson B, Hellstrom PA: A study of hearing changes among military conscripts in the Swedish Army, Int J Audiology 2006; 45:247-251. IV. Muhr P, Rosenhall U: The influence of military service on auditory health and the efficacy of a hearing conservation program, manuscript
