Effect of asbestos-related pleural fibrosis on excursion of the lower chest wall and diaphragm

To examine mechanisms responsible for reduced lung volumes (restriction) in asbestos-related pleural fibrosis (APF), we studied diaphragm function and lower rib-cage excursion in 26 subjects with previous asbestos exposure an d no evidence of asbestosis. Using posteroanterior (PA) and lateral chest r adiographs taken at residual volume and at 25%, 70%, and 100% vital capacit y (VC) during a slow inspiratory maneuver, we measured fractional expansion of the lower rib cage (FErc), fractional shortening of the diaphragm (FSdi ), and changes (Delta) in diaphragm dome height (Hdo) and subphrenic volume (Vdi). Vdi was estimated by measuring the major and minor axes of the subp hrenic space at 1-cm intervals, assuming an elliptical cross-sectional shap e, and correcting for the volume of spinal and paraspinal tissues. Seven su bjects had no evidence of APF (control), 12 had pleural plaques (PP), and s even had diffuse pleural thickening with costophrenic obliteration (DPT). O ver the range of VC, results (mean +/- SEM, normalized for height) in contr ol subjects were VC = 101.2 +/- 4.0 % predicted and Delta Vdi = 326 +/- 8 m l/m(3), and for the right hemithorax and hemidiaphragm on the PA film, FErc = 0.07 +/- 0.05 FSdi = 0.32 +/- 0.02 and Delta Hdo = 0.8 +/- 0.2 cm/m. Rel ative to controls: DPT subjects had reduced VC (77.4 +/- 4.9%, p < 0.01), D elta Vdi (256 +/- 2 ml/m3, p < 0.01), FErc (0.01 +/- 0.02, p < 0.01), FSdi (0.24 +/- 0.01, p < 0.001), and Delta Hdo (-0.9 +/- 0.06 cm/m, p < 0.01); P P subjects had reduced FSdi (0.25 +/- 0.01, p < 0.001) and Delta Vdi (233 /- 47 ml/m(3), p < 0.01), and no difference in FErc, Delta Hdo, or VC. We c onclude that restriction in DPT is due to obliteration of the zone of appos ition, and that by limiting separation of the diaphragm from the rib cage d uring inspiration, this reduces volume contributed by motion of the diaphra gm and lower rib cage. Reduction in the latter contribution was the main ca use of restriction, because the reduction in volume contributed by the diap hragm was partly compensated by flattening of its dome.