Abstract
Plots of published values of the ratio of the residual volume to the total lung capacity against age suggested a curvilinear relationship in which the increase in this ratio with age was more rapid in older subjects than in younger ones. This study of 111 subjects 9 to 77 yr of age showed a probably significant additional reduction in variance by using a 2 segment prediction of the ratio as a function of age rather than a simple linear correlation. This 2 segment prediction includes the predicted values for subjects 9 to 18 yr of age in a common prediction with those 18 to 77 yr of age. There was no significant difference in the values of this ratio for males and females. The prediction suggested that aging of the lung in this respect begins to become noticeable at approximately 35 to 40 yr. In addition, there was evidence that in subjects older than 18 yr, the actual ratio is smaller than the mean predicted value if the vital capacity is larger than the average predicted value. Constants for algebraic prediction of the ratio of residual volume to total lung capacity and a graph for this prediction were developed.