[Age changes in interalveolar septa and their relationship to a decrease in gas exchange]

External respiration and interalveolar septa ultrastructure were examined in healthy men aged 45-49 and 60-70 years. Involution reduction of static lung volumes, decrease in lung ventilation capacity and deceleration of gas exchange in the respiratory portion of the lung were noted. Age changes in interalveolar septa capillary network structure, air-blood barrier and the interstitium have been established. In the elderly people, the capillary network was found to lose some small loops, which were substituted by a connective tissue. The thickness of air-blood barrier was shown to increase, thus causing a deceleration of oxygen diffusion from alveolar lumen into the blood of pulmonary capillaries. The interstitial connective tissue was found to contain a larger proportion of collagen and, particularly, of elastic fibers per unit volume. In the aged persons interalveolar septa underwent obvious sclerotic changes, and the disappearance of Kohn pores could be considered as one of their manifestations. All these changes seem to disturb the uniformity of intraacinar ventilation and may significantly influence gas exchange conditions.