Partitioning airway and lung tissue resistances in humans: effects of bronchoconstriction

David W. Kaczka, Edward P. Ingenito, Bela Suki, and Kenneth R. Lutchen Department of Biomedical Engineering, Boston University, Boston 02215; and Pulmonary Division, Brigham and Women's Hospital, Boston, Massachusetts 02115 Received 20 September 1996; accepted in final form 2 January 1996. Kaczka, David W., Edward P. Ingenito, Bela Suki, and Kenneth R. Lutchen. Partitioning airway and lung tissue resistances in humans: effects of bronchoconstriction. J. Appl. Physiol. 82(5): 1531-1541, 1997. The contribution of airway resistance (Raw) and tissue resistance (Rti) to total lung resistance (R L ) during breathing in humans is poorly understood. We have recently developed a method for separating Raw and Rti from measurements of R L and lung elastance (E L ) alone. In nine healthy, awake subjects, we applied a broad-band optimal ventilator waveform (OVW) with energy between 0.156 and 8.1 Hz that simultaneously provides tidal ventilation. In four of the subjects, data were acquired before and during a methacholine (MCh)-bronchoconstricted challenge. The R L and E L data were first analyzed by using a model with a homogeneous airway compartment leading to a viscoelastic tissue compartment consisting of tissue damping and elastance parameters. Our OVW-based estimates of Raw correlated well with estimates obtained by using standard plethysmography and were responsive to MCh-induced bronchoconstriction. Our data suggest that Rti comprises ~40% of total R L at typical breathing frequencies, which corresponds to ~60% of intrathoracic R L . During mild MCh-induced bronchoconstriction, Raw accounts for most of the increase in R L . At high doses of MCh, there was a substantial increase in R L at all frequencies and in E L at higher frequencies. Our analysis showed that both Raw and Rti increase, but most of the increase is due to Raw. The data also suggest that widespread peripheral constriction causes airway wall shunting to produce additional frequency dependence in E L . airway resistance; inhomogeneities; airway wall shunting; forced oscillations; methacholine 0161-7567/97 $5.00 Copyright © 1997 the American Physiological Society