Airflow resistance in lower airway of the dog

¹ Department of Internal Medicine, University of Minnesota, Minneapolis, and Division of Internal Medicine, Ancker Hospital, St. Paul, Minnesota

The resistance of the lower airway was measured in dogs by an adaptation of the esophageal-balloon method. In normal dogs resistance was found to be lower than previously reported values and not appreciably changed by flow or volume. In dogs with increased resistance, induced either acutely by pilocarpine inhalation or chronically by repeated exposure to phosgene, resistance decreased with increasing volume. However, resistance was not found to increase with increasing flow, supporting the concept that flow in the lower airway is laminar, at least at the flow rates studied. This changing resistance observed during tidal breathing suggests that a single value for resistance cannot adequately describe the dynamic mechanical behavior of the lung under conditions of increased resistance. The technique described for measuring lower-airway resistance may be useful in the evaluation of the bronchomotor effects of drugs.