Frequency dependence and partitioning of respiratory impedance in dogs

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Abstract
Total pulmonary resistance (Rt) and reactance (Xt) from 1 to 30 Hz were determined by time series analysis in open-chest vagotomized dogs. Rt and Xt were partitioned by retrograde catheter into central airway resistance (Rc) and reactance (Xc) and peripheral resistance (Rp) and reactance (Xp). Rt, Rc, or Rp did not change with transpulmonary pressure (Pst) from 5 to 15 cmH2O, although Rc tended to decrease and Rp to increase. Vagal stimulation (Vs) and i.v. histamine (H) increased all resistances (R) at all lung volumes (V) and produced an inverse relationship between R and V. The increases in Rt produced by H and Vs were not significantly different at any volume, but H predominantly increased Rp and Vs predominantly increased Rc. In the control (vagotomized) dogs at Pst of 5 cmH2O, Rp/Rt was 0.41 .+-. 0.03 (SE). Rp/Rt was significantly increased by H but not by Vs. Control Rt decreased slightly 5-10 Hz and increased 15-30 Hz. The increase of Rt at higher frequencies caused by the frequency dependence of Rc was not changed by H but was augmented by Vs. The slope of Xt and Xc vs. frequency was increased by Vs but not by H. The frequency dependence of Rt and Xt > 10 Hz appears to be caused by inertial losses proximal to the 2 mm airways. Central and peripheral bronchoconstriction caused by Vs and H, respectively, could be differentiated by increased frequency dependence of Rt and Xt above 15 Hz. [This study has relevance for human chronic obstructive lung disease.].