Body mass index and adipose tissue within the airway wall

Abstract

Introduction/Aim: Epidemiological studies have shown overweight or obese asthmatics have more severe disease than those of a healthy weight. This may result from an increased amount of adipose tissue within the airway wall that reduces the transmission of parenchymal elastic loads limiting muscle shortening. The aim of this study was to determine the relationship between Body Mass Index (BMI) and adipose tissue within the airway wall in control subjects (n=16) and cases of nonfatal (NFA, n=21) and fatal (FA, n=16) asthma.

Methods: On transverse airway sections taken from formalin-fixed, paraffin-embedded post-mortem lungs, stained with haematoxylin and eosin, the area of adipose tissue within the outer airway wall was estimated by point counts and expressed as area per mm of basement membrane perimeter (Fat/Pbm).

Results: In airways with Pbm >10mm, Fat/Pbm positively correlated with BMI in control (r=0.65, p=0.009), NFA (r=0.49, p=0.02) and FA (r=0.66, p=0.005), and with outer airway wall thickness in control (r=0.43, p=0.02) and NFA (r=0.55, p=0.005). BMI and the amount of Fat/Pbm was greater in airways 4-10mm Pbm from NFA than in other groups (p<0.05). Similar correlations between Fat/Pbm and BMI were seen in airways 4-10mm Pbm. There was no difference in gender or age between groups.

Conclusion: These data show that the amount of adipose tissue within the airway wall increases with BMI in asthmatic and control subjects and contributes to outer airway wall thickness. While functional studies are required to determine the consequence of airway adipose tissue, we speculate that adipose tissue will increase airway narrowing capacity by reducing the afterload that opposes muscle shortening.