We have wedged a small catheter in airways 2 to 3 mm in diameter in excised human lungs to have measure airway resistance central (R_c) and peripheral (R_p) to this site. In five normal lungs, R accounted for only 25 per cent total airway resistance (R_L) and averaged 0.18 cm of water per liter per second. In seven patients with emphysema R_p was increased from four to 40 times. R_p was also increased in one case of bronchiectasis and another of bronchiolitis. In all, R_c scattered around the normal value. Bronchographic and histologic studies showed that R_p was increased because of mucus plugging, narrowing and obliteration of the small airways.

Disease of small airways may be common to various chronic obstructive lung diseases. Because R_p is normally so small, there may be considerable obstruction in peripheral airways that would affect ventilation distribution and gas exchange but would have little effect on function tests designed to reveal obstruction. When total airway resistance is elevated to a clinically detectable level by disease in the small airways, obstruction is much more severe than is generally recognized.