Effect of length changes on bronchial diameters.

The effect of physiological changes in length on the pressure-diameter (PD) behavior of large, excised, intrapulmonary pig, dog, and human bronchi was studied. Length changes did not alter PD behavior of pig bronchi. Lengthening reduced the diameter of dog bronchi but did not alter the shape of the PD curve. In humans, lengthening reduced the diameter at high transmural pressures but not at zero transmural pressure. The wave-speed theory of flow limitation was used as a first approximation to estimate the effect of the length-induced changes on maximal expiratory flow (Vmax). Use of the usual in situ (parenchyma intact) PD curve would lead to a 16% overestimation of Vmax at 45% total lung capacity (TLC) in dog and to a 17% underestimation at 64% TLC in humans. The effect in humans was age dependent and was most pronounced in subjects more than 40 yr of age.