Halothane decreases both tissue and airway resistances in excised canine lungs

Studies of the anesthetic effects on the airway often use pulmonary resistance (RL) as an index of airway caliber. To determine the effects of the volatile anesthetic, halothane, on tissue and airway components of RL, we measured both components in excised canine lungs before and during halothane administration. Tissue resistance (Rti), airway resistance (Raw), and dynamic lung compliance (CL, dyn) were determined at constant tidal volume and at ventilatory frequencies ranging from 5 to 45 min-1 by an alveolar capsule technique. Halothane decreased RL at each breathing frequency by causing significant decreases in both Raw and Rti but did not change the relative contribution of Rti to RL at any frequency. Halothane increased CL,dyn at each breathing frequency, although there was little change in the static pressure-volume relationship. The administration of isoproterenol both airway and tissue components of RL; it may act by relaxing the contractile elements in the lung. Both components must be considered when the effects of volatile anesthetics on RL are interpreted.