Stereological approach to the pathology of lung aging in humans

Knowing lung structure during aging is important to understand the physiology of the senile process and related pathologies, such as COPD. There are scarce pathological data in humans. Aim: To assess, using stereology, lung volume and its compartments in adults and elderly human lungs. Methods: Ten autopsy right lungs from non-smokers, without lung pathology were obtained after ethical approval. Lungs were tracheally inflated with fixative under constant pressure of 20mmHg. Subsequently, the lobes were separated, and the total volumes were assessed by Cavalieri method. Lung tissue was sampled by Fractionator according to systematic uniform random sampling principles. Using H&E, we assessed absolute volume and volume density of airways, vessels, alveolar air spaces and septa by Cavalieri method. Results: The Adult Group (n=5) had mean age of 49.8y (46-59), 4M/1F. The Elderly Group (EG) (n=5) had mean age of 74.8y (60-87), 3M/2F. The EG had significantly whole right lung larger air space volume density (VD) (0.44±0.06vs0.52±0.02, p=0.018) and decreased alveolar septa VD (0.37±0.01vs0.32±0.03, p=0.016), also observed in the superior (p= 0.049, 0.021) and middle lobes (p=0.038 air spaces only). No differences were observed for right lung, lobes and compartment absolute volume (normalized by height). There was a positive correlation between age and air space VD (p=0.013, r=0.75) and a negative correlation with septa VD (p=0.034 r=-0.67). Conclusion: Although absolute lung volumes are not altered in EG, there is an altered VD of alveolar air spaces/septa, especially in the upper lobe, that correlates with age. Our stereological data in humans confirm previous experimental studies and radiological findings.