DETECTION OF 2 CLUSTERS OF MECHANICAL-PROPERTIES OF SMOOTH-MUSCLE ALONG THE AIRWAY TREE

Heterogeneity of function of airway smooth muscle along the airways ma y be of great importance in regulating regional ventilation and in the pathogenesis of asthma. To investigate the distribution of mechanical properties of airway smooth muscle along the airway, muscle strips fr ee of cartilage and epithelium from the trachea down to bronchial gene ration 6 were studied by employing electrical field stimulation. Resul ts showed that smooth muscle mechanical performance decreased progress ively down the airway tree. Cluster analysis further indicated that sm ooth muscle from these airways could be divided into two groups: 1) an extrapulmonary group, which contains muscle from the trachea and bron chial generations I and 2 and is characterized by higher maximum short ening capacity and zero-load velocity of shortening (V-0) in early sho rtening, the expected decrease of V-0 values (the so-called latch phas e) in the later phase of shortening, and lower sensitivity to stimulat ion; and 2) an intrapulmonary group, which contains bronchi from gener ations 3-6 and has a lower maximum shortening capacity and V-0 in earl y shortening but higher sensitivity to stimulation. The relatively low er mechanical performance of intrapulmonary bronchial smooth muscle ma y represent a safety device that prevents excessive smooth muscle shor tening in vivo.