ACUTE PULMONARY RESPONSE TO INTRAVENOUS HISTAMINE USING FORCED-OSCILLATIONS THROUGH ALVEOLAR CAPSULES IN DOGS

We measured the time course of alveolar input impedance using two alveolar capsule oscillators after intravenous bolus administration of 20 mg of histamine in open-chest dogs. Impedances (24-200 Hz) were obtained every 2 s after an injection for 100 a. Each impedance was fit with a model consisting of a pathway (with resistance and inertance) leading from the alveolar capsule into a subpleural region (with elastance EA) that, in turn, was connected to the lung compartment (consisting of the remainder of the lung and positive end-expiratory pressure system) via another pathway (with resistance RA). In all cases (6 dogs, 2 capsules each), the resistance and inertance leading from the alveolar capsules were negligible. The correlation of the relative increases in RA obtained from the two capsule oscillators in each dog was not significant. The correlation for EA also was not significant. The times at which RA achieved values of 20% greater than baseline were not significantly correlated between the two capsules, as was the case for EA. However, the baseline values of EA and RA from a given capsule were significantly correlated, as were their fractional increases with histamine. These results show that both the magnitude and timing of changes in local lung resistance and elastance are spatially extremely heterogeneous.