Estimation of diaphragm length in patients with severe chronic obstructivepulmonary disease

In patients with advanced chronic obstructive pulmonary disease (COPD) diap hragm function may be compromised because of reduced muscle fibre length. D iaphragm length (L-Di) can be estimated from measurements of transverse dia meter of the rib cage (D-Re) and the length of the zone of apposition (L-Za pp) in healthy subjects, but this method has not been validated in patients with COPD. Postero-anterior chest radiographs were obtained at total lung capacity (TLC), functional residual capacity (FRC) and residual volume (RV) in nine male patients with severe COPD (mean [S.D.]; FEV1, 23 [6] %pred.; FRC, 199 [15] %pred.). Radiographs taken at TLC were used to identify the l ateral costal insertions of the diaphragm (L-Zapp assumed to approach zero at TLC). L-Di was measured directly and also estimated from measurements of L-Zapp and D-Rc using a prediction equation derived from healthy subjects. The estimation of L-Di was highly accurate with an intraclass correlation coefficient of 0.93 and 95% CI of similar to +/- 8% of the true value, L-Di decreased from 426 (64) mm at RV to 305 (31) mm at TLC. As there were only small and variable changes in D-Rc across the lung volume range, most of t he L-Di changes occurred in the zone of apposition. Additional studies show ed that measurements of L-Di from PA and lateral radiographs performed at d ifferent lung volumes were tightly correlated. These results suggest that n on-invasive measurements of L-Zapp in the coronal plane (e.g. using ultraso nography) and D-Re (e.g. using magnetometers) can be used to provide an acc urate estimate of L-Di in COPD patients. (C) 2000 Elsevier Science B.V. All rights reserved.