Diaphragmatic volume contribution estimated from a single radiographic plane

We have previously shown that the volume displaced by diaphragm motion (AVdi) can be estimated from paired posteroanterior (PA) and lateral chest x-rays at multiple lung volumes by dividing the volume contained within the dome, zone of apposition, and insertions of the diaphragm into multiple horizontal elliptical slices, and correcting for spinal volume (Vsp) (Singh et al, AJRCCM 1998;157:A663).To determine the feasibility of estimating AVdi using fluoroscopy from a single radiographie plane, we compared the results of AVdi (expressed as % of inspired volume measured by pneumotach, AVdi:%Vm) obtained by our method (SinghPASLA7) with that of (a) Verschakelen et al (JAP 1992;72:1536-40) applied to lateral chest x-rays (Ver) and (b) Petroll et al (JAP 1990;69:2175-82) applied to either PA (PetPA) or lateral (PetUT) chest x-rays, collected at residual volume, 25, 70 and 100 % vital capacity in 17 subjects of whom 6 had pleural plaques and 6 had costophrenic fibrosis. We found that AVdi was over-estimated by Pet _PA and Ver (AVdi:%Vm>100), and relative to our method, under-estimated by Pet (see figure). When these methods were modified by correcting for Vsp, applying actual lower rib cage dimensions and altering the geometric model of the diaphragm, AVdi:%Vm was not different from Singh _PMLAT (p>0 05. ANOVA). We conclude that estimates of AVdi can be obtained from a single radiographie plane by simple modifications of existing methods. Although these modifications result in concordant results across methods, they require validation and assessment of accuracy, i.