How many licks does it take to get to the middle of a Tootsie Roll Pop? How many angels can dance on the head of a pin? And that other timeless mystery: How many airways do patients with COPD have, how narrowed are they, and what is the relationship between said narrowing, coexisting emphysematous destruction, and airflow limitation? One of these seemingly unanswerable questions was addressed in the New England Journal of Medicine this week.
McDonough et al collected chest CTs of 78 people with COPD. They also gathered 14 explanted lungs donated by people with COPD and 4 healthy donated lungs (which were "wasted" after no matching lung transplant recipients were found). They sliced up the lungs, performed micro-CT on them and matched exactly the various samples/images (fixed tissue, micro-CT of fixed tissue, and CT of live people with COPD) for comparison with each other.
The number of airways 2.0 to 2.5 mm in diameter were progressively reduced according to stage of COPD. The microCT scans of lungs removed from people with GOLD stage IV COPD had lost a whopping 81 to 99.7% of the total cross-sectional area of terminal bronchioles, and 72 to 89% of the number of terminal bronchioles, compared to the healthy donor lungs.
Emphysematous changes were also identified and were progressive with GOLD stage. However, the small airway narrowing/destruction preceded the emphysematous changes.
Authors conclude it's this small-airway narrowing and destruction that cause increased airflow resistance in COPD, well before emphysematous destruction contributes substantially. And they have the chopped-up lungs to prove it.
McDonough JE et al. Small-Airway Obstruction and Emphysema in Chronic Obstructive Pulmonary Disease. N Engl J Med 2011;365:1567-1575.