Changes occurring with increasing age in the rat lung: Morphometrical study

Background: It was hypothesized that the evolution towards the senile lung is progressive, being initiated in the adult stage; and for this reason changes similar to those described in the senile lung can be detected in the lungs of middle‐aged rats. To test the hypothesis, the following design was used. The lungs of two groups of rats, adult (mean age of 16 weeks) and middle‐aged (mean age of 56 weeks) were morphometrically compared. Methods: Thirty‐one Wistar rats were used for the study; their lungs were processed histologically. The microscopic fields were analysed in a computer, and 20 variables were quantified. These were grouped into (a) variables which describe the shape and size of the distal airspace, (b) variables which describe the distal lung tissue, and (c) variables which describe elastic fibers. The results were statistically compared: correlation tests were carried out, and the specificity, sensitivity, and misclassification indices were calculated. Results: All the results of the variables which define the size of the air‐spaces were found to be significantly higher (P