To examine the effect of hyperinflation on pump function of the diaphragm we compared 9 subjects with emphysema and severe hyperinflation (mean TLC 1 33%R RV/TLC ratio 0.65) with 10 healthy controls matched for gender, age, height and body mass index. Using posteroanterior and lateral chest radiographs taken at RV, FRC, FRC + 1/2 inspiratory capacity and TLC, we measured changes in diaphragm length (Ldi), dome height (Hdo) and shape factor (Kdo = dome length/rib cage diameter), fractional expansion of the rib cage (FErc) and subphrenic volume (Vdi). Vdi was estimated by measuring its major and minor axes at 1 cm intervals, assuming an elliptical cross- sectional shape, and correcting for spinal volume. Results (mean ±SD,p < 0.05, f p < 0.01, $ p < 0.001) for changes between RV and TLC in the sagittal plane unless specified are tabulated below. We found that relative to controls, subjects with emphysema had reduced Ldi at RV (LdiRV), ALdi, shortening in the zone of apposition (ALzapp), AHdo (coronal plane) and ratio of lower/mid rib cage expansion (FErc UM). In contrast AVdi was not different from controls and the contribution of the diaphragm to vital capacity (AVoVNC) was normal. In the sagittal plane Kdo at TLC approached unity indicating an extremely flat diaphragm. We conclude that in emphysema diaphragm flattening during a vital capacity inspiration results in (1) preservation of volume contribution of the diaphragm despite a reduced initial length at RV and reduced shortening in the zone of apposition, and (2) a relative reduction in lower rib cage expansion.
- Volume contribution