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In this study, we report the development and accuracy of a direct technique to measure airway calibre using a superfine fibreoptic bronchoscope. Ten mongrel dogs were anaesthetized with pentobarbitone and the trachea intubated with a tracheal tube; the small lumen of the tube allowed passage of a superfine fibreoptic bronchoscope (od 2.2 mm). Bronchial cross-sectional area and airway pressure were recorded continuously and dynamic pulmonary compliance and airway resistance calculated. The dogs were allocated to one of two groups. In the first group (six dogs), bronchoconstriction was induced with histamine 10 micrograms kg-1 i.v. and 500 micrograms kg-1 h-1 c.i.v. Thirty minutes later, adrenaline 0-0.4 mg kg-1 was given i.v. Bronchial cross-sectional area, dynamic pulmonary compliance and airway resistance were assessed simultaneously. In the second group, 0.9% saline was given 30 min after placement of the superfine fibreoptic bronchoscope and 10 min later atropine 0.1 microgram kg-1 was administered. In the first group, histamine decreased mean percentage bronchial cross-sectional area by 49.2 (SD 11.5) %, reduced dynamic pulmonary compliance from 32.1 (12.6) to 22.3 (5.2) ml cm H2O-1 and increased airway resistance from 39.1 (11.6) to 57.2 (10.2) cm H2O litre-1 s-1. Adrenaline produced a dose-dependent increase in percentage bronchial cross-sectional area and dynamic pulmonary compliance to 119.4 (31.3)% and 27.4 (5.5) ml cm H2O-1, respectively, and a decrease in airway resistance to 43.9 (7.2) cm H2O litre-1 s-1. There were significant correlations between percentage bronchial cross-sectional area and dynamic pulmonary compliance (r = 0.720, P < 0.0001) and airway resistance (r = 0.727, P < 0.0001). Atropine 0.1 mg kg-1 increased basal bronchial cross-sectional area to 137.5 (16.9) %. These data indicate that adrenaline reversed histamine- and pentobarbitone-induced bronchoconstriction.

Droperidol has been reported to cause bronchodilatation but its mechanism(s) of action is unknown. We have evaluated the spasmolytic effect of droperidol on histamine- and serotonin (5-HT)-induced bronchoconstriction in dogs. Bronchial cross-sectional area was assessed with a superfine fibreoptic bronchoscope. Twenty-eight mongrel dogs were allocated randomly to one of two groups (histamine and 5-HT) to receive either histamine or 5-HT to induce bronchoconstriction. Changes in bronchial cross-sectional area were presented as percentage of basal bronchial cross-sectional area. Continuous i.v. infusion of histamine 500 micrograms kg-1 h-1 or 5-HT 500 micrograms kg-1 h-1 decreased percentage bronchial cross-sectional area by 46.4 (14.3)% or 68.9 (13.7)%, respectively. In both groups, droperidol reversed bronchoconstriction in a dose-dependent manner. In the histamine but not in the 5-HT group, plasma adrenaline and noradrenaline concentrations increased significantly after i.v. droperidol. In addition, propranolol antagonized droperidol-induced relaxation in the histamine but not in the 5-HT group. Our data indicate that the spasmolytic effect of droperidol on canine airway was caused, at least in part, by both catecholamine releases and 5-HT receptor antagonism.

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