PARTITIONING AIRWAY AND LUNG-TISSUE RESISTANCES IN HUMANS - EFFECTS OF BRONCHOCONSTRICTION

The contribution of airway resistance (Raw) and tissue resistance (Rti ) to total lung resistance (RL) during breathing in humans is poorly u nderstood. We have recently developed a method for separating Raw and Rti from measurements of RL and lung elastance (EL) alone. In nine hea lthy, awake subjects, we applied a broad-band optimal ventilator wavef orm (OVW) with energy between 0.156 and 8.1 Hz that simultaneously pro vides tidal ventilation. In four of the subjects, data were acquired b efore and during a methacholine (MCh)-bronchoconstricted challenge. Th e RL and EL data were first analyzed by using a model with a homogeneo us airway compartment leading to a viscoelastic tissue compartment con sisting of tissue damping and elastance parameters. Our OVW-based esti mates of Raw correlated well with estimates obtained by using a standa rd plethysmography and were responsive to MCh-induced bronchoconstrict ion. Our data suggest that Rti comprises similar to 40% of total RL at typical breathing frequencies, which corresponds to similar to 60% of intrathoracic RL. During mild MCh-induced bronchoconstriction, Raw ac counts for most of the increase in RL. At high doses of MCh, there was a substantial increase in RL at all frequencies and in EL at higher f requencies. Our analysis showed that both Raw and Rti increase, but mo st of the increase is due to Raw. The data also suggest that widesprea d peripheral constriction causes airway wall shunting to produce addit ional frequency dependence in EL.