CONSERVATION OF BRONCHIOLAR WALL AREA DURING CONSTRICTION AND DILATION OF HUMAN AIRWAYS

We assessed the effect of smooth muscle contraction and relaxation on airway lumen subtended by the internal perimeter (A(i)) and total cros s-sectional area (A(o)) of human bronchial explants in the absence of the potential lung tethering forces of alveolar tissue to test the hyp othesis that bronchoconstriction results in a comparable change of A(i ) and A(o). Luminal area (i.e., A(i)) and A(o) were measured by using computerized videomicrometry, and bronchial wall area was calculated a ccordingly. Images on videotape were captured; areas mere outlined, an d data were expressed as internal pixel number by using imaging softwa re. Bronchial rings were dissected in 1.0- to 1.5-mm sections from mac roscopically unaffected areas of lungs from patients undergoing resect ion for carcinoma, placed in microplate wells containing buffered sali ne, and allowed to equilibrate for 1 h. Baseline, A(o) [5.21 +/- 0.354 (SE) mm(2)], and A(i) (0.604 +/- 0.057 mm(2)) were measured before co ntraction of the airway smooth muscle (ASM) with carbachol. Mean A(i) narrowed by 0.257 +/- 0.052 mm(2) in response to 10 mu M carbachol (P = 0.001 vs. baseline). Similarly, A(o) narrowed by 0.272 +/- 0.110 mm( 2) in response to carbachol (P = 0.038 vs. baseline; P = 0.849 vs. cha nge in A(i)). Similar parallel changes in cross-sectional area for A(i ) and A(o) were observed for relaxation of ASM from inherent tone of o ther bronchial rings in response to 10 mu M isoproterenol. We demonstr ate a unique characteristic of human ASM; i.e., both luminal and total cross-sectional area of human airways change similarly on contraction and relaxation in vitro, resulting in a conservation of bronchiolar w all area with bronchoconstriction and dilation.