Acoustic input impedance of excised dog lungs

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Abstract
Input impedances of 6 excised dog lungs were computed from Fourier analysis of their response to a transient pulse pressure excitation. Impedances, between 156 and 10,000 Hz, were measured at transpulmonary pressures of 30, 20, 10 and 5 cm H2O. There was a substantial amount of interindividual variability in the impedance. There were generally 3 well defined impedance peaks and the frequencies of these peaks seemed to be dependent upon body size and lung volume. If the airways are modeled simply as a constant diameter tube it might be paradoxically concluded that substantial airway closure occurs at relatively large lung volumes. Conditions of open airways are consistent with these results if the airways are modeled as having a more complex geometrical shape. The input impedance at these high frequencies is apparently variable among individuals, and between lung volumes in any given individual. Estimates of pathlength or the alveolar boundary condition cannot be easily obtained by interpretation based on simple geometrical models.

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