Airways Obstruction From Asbestos Exposure: Results
The statistical significance of group differences in means and in mean residuals were virtually identical, with only five differences in 30 comparisons. Three of these were in ex-smokers whose group variances (SDs) are invariably larger.
As the profusion of opacities increased from 0/0 to 3/2 in as men who had never smoked cigarettes FVC, FEVi, FEVi/FVC, FEF25-75, and FEF75-85 decreased, TLC did not change, and RV/TLC increased as shown by regression coefficients (tables may be requested with reprints). ILO profusion explained more of the variance (r2) in RV/TLC (6.6 percent) than in other values (below 3.1 percent). Duration of asbestos exposure was more highly correlated with increased RV/TLC and with decreased FEVi/FVC and the larger adjusted r2s (11 percent and 4 percent) meant that it explained more of the variance than did ILO profusion.
FEF25-75 decreased progressively but TLC was unaffected by increasing duration of exposure. Consequently, RV/ TLC increased, indicating air trapping, and this air trapping progressively reduced FVC. Increases in severity of asbestosis (ILO profusion 0-10) was reflected as progressively greater airways obstruction using FEF25-75 in the box plots of Figure 1 (top) and increased air trapping using RV/TLC in Figure 1 (bottom). flovent inhaler
Regression models in current cigarette smokers showed similar relationships to never smokers with slightly larger proportions of the variance explained by changes in ILO profusion. Duration of asbestos exposure had similar coefficients for FEF25-75 but explained more of the variance in RV/TLC (12.9 percent) and FEVi/FVC (5.7 percent) than did ILO profusion (7.9 percent and 3.3 percent). As most of the variance is due to height, age, and smoking adjusted by the percent predicted, these relatively low values for adjusted r2 are important in choosing the relative contribution of severity of asbestosis and the duration of residence of asbestos in the lung. Mid expiratory flow decreased in current smokers as ILO profusion increased from 0/0 to 3/3 (Fig 2, top) and air trapping, shown by RV/TLC, progressively increased as ILO profusion increased (Fig 2, bottom). Ex-cigarette smokers were similar to current smokers except that the coefficient for FEF75-85 with ILO profusion was not significant.
Figure 1. Top, Mid flows (FEF25-75) in 1,777 men who were never smokers as a percentage of predicted (adjusted for height and age) are shown as box plots against ILO categories 0/0 to 3/3 with median line, 25 percent to 75 percent limits as the box bottoms and tops and whiskers equal to three halves of the interquartile range rolled back to where there are data. Regression equation for FEF25-75 percent predicted=99.01—4.92 ILO category (p<0.0001, R2=2.4 percent). Bottom, Residual volume/ total lung capacity (RV/TLC) is plotted against ILO categories as in top. RV/TLC=36.6+2.54 ILO category (p<0.0001, R2=6.7 percent).
Figure 2. Top, Mid flows (FEF25-75) in 4,550 men who were current smokers as percentage of predicted (adjusted for height* age, and duration of cigarette smoking) are plotted against ILO categories as in Figure 1. FEF25-75 percent predicted=89.4—4.93 ILO category (p<0.0001, R2=3.5 percent). Bottom, Residual volume/total lung capacity (RV/TLC) is plotted against ILO categories for current smokers. RV/TLC=41.2+2.04 ILO category (p<0.0001, R2=7.9 percent).