Measurement and mathematical modelling of elastic and resistive lung mechanical properties studied at sinusoidal expiratory flow.

Summary Elastic pressure/volume (P(el)/V) and elastic pressure/resistance (P(el)/R) diagrams reflect parenchymal and bronchial properties, respectively. The objective was to develop a method for determination and mathematical characterization of P(el)/V and P(el)/R relationships, simultaneously studied at sinusoidal flow-modulated vital capacity expirations in a body plethysmograph. Analysis was carried out by iterative parameter estimation based on a composite mathematical model describing a three-segment P(el)/V curve and a hyperbolic P(el)/R curve. The hypothesis was tested that the sigmoid P(el)/V curve is non-symmetric. Thirty healthy subjects were studied. The hypothesis of a non-symmetric P(el)/V curve was verified. Its upper volume asymptote was nearly equal to total lung capacity (TLC), indicating lung stiffness increasing at high lung volume as the main factor limiting TLC at health. The asymptotic minimal resistance of the hyperbolic P(el)/R relationship reflected lung size. A detailed description of both P(el)/V and P(el)/R relationships was simultaneously derived from sinusoidal flow-modulated vital capacity expirations. The nature of the P(el)/V curve merits the use of a non-symmetric P(el)/V model.