Tobacco smoke and age as risk factors in emphysema. Morphometrical study on the rat.

During ageing, a progressive deterioration in the pulmonary function, which can be accelerated by exposure to tobacco smoke, takes place. The hypothesis that the initial age of exposure to tobacco smoke is a factor of utmost importance in the development of emphysema is proposed. Eighty-six rats, aged nineteen months at the time of sacrifice, were used and were ordered into three groups: the first group consisted of unmanipulated animals; the second, of animals which had been exposed to tobacco smoke from the age of twelve months to the age of nineteen months; and the third, of animals which had been exposed to tobacco smoke from the age of nine months to the age of twelve months. The lungs of the animals were histologically processed for light microscopy and were studied morphometrically by computer. Eleven quantitative variables were quantified and ordered into three groups: variables related with alveolar enlargement; variables related with tissue loss; and variables related with the elastic fibre. The number of animals in which alveolar enlargement and tissue destruction concurred was counted, thus enabling the attributable and relative risks of developing emphysema to be calculated in the two groups of manipulated animals. From the results it is clear that, when compared with the unmanipulated group, the two groups which had been exposed to tobacco smoke displayed an increase in the variables which quantified alveolar enlargement and a decrease in those which measured tissue loss; these results were more significant in the third group (p < 0.001) than in the second (p < 0.05); significant differences were also found between these two groups of animals. The relative risk and attributable risks of developing emphysema were 2.41 and 28.15 respectively in the second group and 3.48 and 34.48 in the third group. Our results lead us to propose that the risk of developing emphysema exists in inverse proportion to the initial age of exposure to tobacco smoke.