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.

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.

Exposures to lead during urban combat training.

Lead exposure is still a major concern for occupations that regularly train or work with firearms, such as law enforcement and military personnel. Due to the increasing number of women of fertile age in such professions, there is a strong incentive to monitor lead exposures during firearms training. Personal air sampling was performed during two sessions of a nine-day urban combat training (UCT) course for cadets in the Swedish Armed Forces, one session employing leaded ammunition (leaded scenario) and one session employing unleaded ammunition (unleaded scenario). Blood lead levels (BLLs) were measured before and after the course for 42 cadets and five instructors. During the leaded scenario, the instructors' airborne exposure (geometric mean, GM, 72.0 µg/m3) was higher than that of cadets (GM 42.9 µg/m3). During the unleaded scenario, airborne concentrations were similar for instructors and cadets and considerably lower than during the leaded scenario (GM 2.9 µg/m3). Despite comparably low external lead exposures during the course, we saw a statistically significant increase in systemic exposure for cadets (BLL GM increased from 1.09 to 1.71 µg/dL, p < 0.001). For the five instructors, notable differences were seen depending on task. The largest increase was seen for the two instructors performing close supervision during the leaded scenario (BLL GM increased from 2.41 µg/dL to 4.83 µg/dL). For the remaining three instructors the BLLs were unchanged (BLL GMs were 1.25 µg/dL before the course and 1.26 µg/dL after). None of the participants exceeded the applicable biological exposure limits, but extrapolating our findings shows that instructors in the leaded scenario may reach levels around 10 µg/dL after a year of repeated exposures. We conclude that comparably low airborne concentrations can contribute to the body burden of lead and that additional measures to reduce exposure are warranted, particularly for instructors.