Relationship between collateral flow resistance and alveolar pores in the aging beagle dog.

Controversy exists over the effect of aging on the alveolar pores of Kohn and the functional relevance of observed changes in alveolar pore structure. We investigated the relationship between collateral resistance (Rcoll), as a measurement of the resistance to collateral flow through collateral channels, and the change in number and size of alveolar pores in the aging beagle dog. Healthy beagle dogs from a closed colony were divided into five groups having mean ages of 3, 6, 9, 12, and 14 yr. Rcoll was measured in anesthetized dogs using a wedged-catheter technique. Following euthanasia, the dogs were necropsied, and the same lung lobe was microdissected along a major intrapulmonary airway, allowing sampling of terminal and respiratory bronchioles from the same airway generation in each dog. Scanning electron microscopy was performed on alveoli adjacent to these bronchioles. There was a significant rise in Rcoll with age. Alveolar pore size and number increased significantly with age, which would be anticipated to reduce Rcoll if the alveolar pores provided a major pathway for collateral ventilation in the dog lung. These findings suggest that the alveolar pores are functionally inoperative for collateral ventilation in the lung at functional residual capacity, possibly because they remain closed at a low lung volume and/or are covered by surfactant.