Airway flow limitation in patients with vibroacoustic disease

Vibroacoustic disease (VAD) is a pathology caused by occupational exposure to large pressure amplitude and low frequency (LPALF) noise (> or =90 dB SPL, < or =500 Hz), and has been the object of study by this group for the past 20 yr. In a group of 140 VAD-diagnosed patients, 7 non-smoker aircraft technicians developed clinical signs of respiratory insufficiency at an early age. Previously, multi-focal fibrosis had been observed in the lung of Wistar rats exposed to occupationally simulated LPALF noise and with no possibility of contamination by fumes, dust or other chemical agents. The goal of this study is to compare pulmonary imaging and/or functional changes in two age- and exposure-time matched groups of VAD-diagnosed aircraft technicians, with and without airflow limitation symptoms.

In a population of 140 individuals occupationally exposed to LPALF noise and diagnosed with VAD, we excluded the smokers (45 cases) and selected 7 individuals with complaints of airway flow limitations, average age 42.3 yr (SD = 2.3). From the remaining non-smokers without respiratory complaints, we selected a group of 15, age-matched patients (average age 36 yr, SD = 6.5). All subjects received a high-resolution CT scan of the chest and respiratory function tests consisting of body plethysmography, spirometry and metacholine airway provocation.

There is a significant relationship between the presence of symptoms and imaging of lung fibrosis through high-resolution CT scan (p = 0.03624). There are no significant differences when both groups are compared with respect to the percentage of predicted values of lung function: Vital Capacity (VC), Total Lung Capacity, Forced Expiratory Volume during the first second of expiration, Maximal Expiratory Flow at 50% VC, Total Airway Resistance, and Airway Reactivity after 25 mg of metacholine.

High resolution CT scan is a valuable tool for diagnosis of lung fibrosis in VAD patients who have symptoms of airway flow limitations. The fact that lung ventilation tests did not present significant changes between both groups is in agreement with findings in Wistar rats. This strongly suggests that a process of focal pulmonary fibrosis may be induced by occupational noise exposure, and is a feature of VAD.