Morphometry of the distal air spaces in lungs of aging dogs.

Changes in pulmonary morphometric measurements with age were examined by manual and automated methods in 14 normal beagle dogs aged 289-3,694 days. The study was instituted as a statistical adjunct to previous morphological studies on these dogs that showed anthracosis and associated dilatations in the distal airways in aged dogs. With increasing age, the volumetric density of alveolar ducts increased concomitantly with decreases in the volumetric densities of alveoli and alveolar parenchymal tissue. The numerical and surface densities of alveoli also decreased with age. A comparison of an automated method with accepted manual methods showed no significant differences in stereological measurements of the distal air spaces with the exception of an overestimation of surface density by the automated method. The automated method was found to be a satisfactory method for evaluating the relative differences in alveolar surface densities and the volumetric densities of respiratory air space and parenchymal tissue.