The objective of this study is to investigate collateral ventilation in three species with widely different subgross pulmonary anatomy - the cow, the horse, and the dog. Differences in collateral ventilation may explain the different types of chronic lung disease observed in these species and in man. Changes in collateral ventilation with age may also explain the different types of lung disease occurring at different ages within a species of animal. We will measure collateral flow resistance (R subCOL) using a double lumen squid hook catheter wedged in an airway in the lower lobe of excised dog lungs or the accessory lobe of excised cow and horse lungs. Air will flow into the isolated lung segment through the outer lumen while segment pressure is recorded through the inner lumen. Flow will then be arrested and the time constant for collateral flow (T subCOL) determined from the decay of segment pressure. We will examine the effect of lung volume, lung volume history, isolated segment pressure, and animal age on R subCOL and TsubCOL. We also plan to investigate RsubCOL and TsubCOL in spontaneously occurring obstructive lung disease of horses and to create airway obstructions in dogs and horses using beads and follow collateral ventilation for several weeks after airway obstruction. Frequency dependence of compliance will be used to evaluate collateral ventilation in this latter experiment.