Effects of smoking and occupational exposure on peripheral airway function in young cereal grain workers

We studied two groups of young male cereal grain elevator workers: 82 lifetime nonsmoking grain workers (2.5 +/- 1.2 yr of dust exposure) who were 22.7 +/- 3.5 yr of age, and 82 smoking grain workers (6.1 +/- 4.1 pack-years of smoking) individually matched to the nonsmoking grain workers for age (22.7 +/- 3.3 yr) and years of work in the grain industry (2.6 +/- 1.3 yr). We also studied the following groups of community control subjects: 82 nonsmoking community control subjects individually matched to the nonsmoking grain workers for age (22.8 +/- 3.7 yr), and 82 smoking community control subjects individually matched to the smoking grain workers for age (22.7 +/0 3.6 yr) and smoking history (6.0 +/- 4.0 pack-years). We measured forced expiratory volume in one second (FEV1), forced vital capacity (FVC), FEV1/FVC %, the maximal mid-expiratory flow rate (FEF25-75), the flow at 50% (Vmax50) and 25% (Vmax25) of a maximal expiratory flow-volume maneuver, the percent increase in the maximal expiratory flow at 50% FVC breathing a mixture of 80% helium-20% oxygen as compared with air (delta Vmax50), and the slope of Phase III of the single breath nitrogen test (delta N2/L). We also assessed the prevalence of respiratory symptoms from responses to a standardized questionnaire. Smoking was associated with an increased prevalence of cough, wheezing, and dyspnea, and a mildly decreased FEV1/FVC %. Two variables were used as indexes of small airway dysfunction, a lower delta Vmax50 and a higher delta N2/L. Only the group of workers who both smoked and were occupationally exposed to grain dust had evidence of small airway dysfunction. The differences in delta N2/L and delta Vmax50 were greater than was expected from an additive model, suggesting that the combined effects of occupational exposure to grain dust and inhalation of cigarette smoke may have a synergistic effect leading to small airway dysfunction in young cereal grain workers.