To examine the effect of hyperinflation on the volume displaced by diaphragm motion (DeltaVdi), we compared nine subjects with emphysema and severe hyperinflation [residual volume (RV)/total lung capacity (TLC) 0.65 +/- 0.08; mean +/- SD] with 10 healthy controls. Posteroanterior and lateral chest X rays at RV, functional residual capacity, one-half inspiratory capacity, and TLC were used to me...