1. Exponential analysis of lung pressure-volume curves is used to deal with the non-linearity of the pressure-volume relationship. A major problem of this procedure is to define the lower volume limit for exponential curve fitting.
2. In 12 healthy subjects and 24 patients with chronic airflow obstruction, a cubic function was fitted to the quasi-static pressure-volume curves to define an inflection point.
3. The exponential function of Colebatch et al. (Colebatch, H.J.H., Ng, C.K.Y. & Nikov, N. J. Applied Physiol. 1979; 46, 387–93) was then fitted to the data for volumes above the inflection point.
4. Exponential analysis with a cubic determination of an inflection point provides an objective way to describe the elastic properties of the human lungs in vivo.