Partitioning of lung tissue response and inhomogeneous airway constriction at the airway opening

Suki, Béla, Huichin Yuan, Qin Zhang, and Kenneth R. Lutchen. Partitioning of lung tissue response and inhomogeneous airway constriction at the airway opening. J. Appl.Physiol. 82(4): 1349-1359, 1997.During abronchial challenge, much of the observed response of lung tissues isan artifactual consequence of inhomogeneous airway constriction.Inhomogeneities, in the sense of time constant inequalities, are aninherently linear phenomenon. Conversely, if lung tissues respond to abronchoagonist, they become more nonlinear. On the basis of thesedistinct responses, we present an approach to separate real tissuechanges from airway inhomogeneities. We developed a lung model thatincludes airway inhomogeneities in the form of a continuousdistribution of airway resistances and nonlinear viscoelastic tissues.Because time domain data are dominated by nonlinearities, whereasfrequency domain data are most sensitive to inhomogeneities, we apply acombined time-frequency domain identification scheme. This model wastested with simulated data from a morphometrically based airway modelmimicking gross peripheral airway inhomogeneities and shown capable ofrecovering all tissue parameters to within 15% error. Application toour previously measured data suggests that in dogs during histamine infusion 1) the distribution ofairway resistances increases widely and2) lung tissues do respond but lessso than previously reported. This approach, then, is unique in itsability to differentiate between airway and tissue responses to anagonist from a single broadband measurement made at the airway opening.