Small Airways Disease in Chronic Obstructive Pulmonary Disease: A 50 Years History

Abstract

Macklem and Mead provided the first direct evidence that the small conducting airways < 2 mm in diameter accounted for less than 10% of the total lower airway resistance in 1967. This seminal report was followed by Hogg, Macklem, and Thurlbeck's 1968 report that confirmed and extended these observations by showing that the same small airways that offer so little resistance to airflow in normal human lungs become the major site of obstruction in patients with emphysema. These and other observations led Mead to postulate that these small conducting airways represent a "quiet" zone within the normal lung where disease can accumulate over many years without being noticed. This brief review revisits this hypothesis within the context of work reported in the 50 years since Macklem and Mead published their work. With special emphasis on why these small conducting airways are vulnerable to the development of disease.