Exponential analysis of lobar pressure-volume characteristics.

In 19 excised left human lungs, seven of which were emphysema-free, lobar pressure-volume (P-V) characteristics were analysed by fitting to the P-V data an exponential of the form V=A-Be-KPL (where V is the volume at a transpulmonary pressure (PL), A is the theoretical lung volume at infinite PL, B is the difference between A and the intercept of the fitted exponential on the volume axis and K is a shape constant). In the emphysema-free lungs there was no difference in the B/A ratio expressed as a percentage, indicating an identical position of the P-V curves of the upper and lower lobes. However the upper lobes had significantly (p less than 0.025) higher values for K than the lower lobes indicating greater compliance. In 10 emphysematous lungs the upper lobes were more severely involved than the lower lobes. In these lungs the difference in K between upper and lower lobes had been abolished suggesting that the less emphysematous lower lobes had increased compliance relatively more than the upper lobes.