WAVE-PROPAGATION, INPUT IMPEDANCE, AND WALL MECHANICS OF THE CALF TRACHEA FROM 16 TO 1,600 HZ

Propagation of waves in the airways is important in flow limitation as well as in oscillation mechanics. In five excised calf tracheae, we m easured phase propagation velocity (c) and input impedance with open ( Z(op)) or closed end (Z(cl)) for frequencies (f) between 16 and 1,600 Hz at two axial tensions [nonstretched (T-N) and stretched (T-S); T-S > T-N]. From 16 to 64 Hz, c slightly increased because of the viscoela stic properties of the wall tissues. Between 64 and 200 Hz, c was rela tively constant and less than the free-field speed of sound (c(o) = 34 0 m/s), with values smaller at T-s (140 +/- 39 m/s) than at T-N (172 /- 35 m/s). Above 200 Hz, c exceeded c(o) and displayed two maxima at similar to 300 and similar to 700 Hz, with values of similar to 360 an d similar to 550 m/s, respectively. For f > 1,400 Hz, c approached c(o ). We provide evidence that the two maxima in c were the result of the two-compartment behavior of the wall tissues, i.e., the separate cart ilaginous and soft tissues. A nonrigid tube model with its wall impeda nce composed of two series resistance, compliance, and inertance pathw ays in parallel simultaneously fits c, Z(op), and Z(cl)ides a link amo ng these data. By use of the relationship between volumetric wall para meters and the tracheal geometry, separate material properties such as viscosity and Young's modulus of both the soft tissue (similar to 1 c mH(2)O.s and similar to 0.26 X 10(4) cmH(2)O, respectively) and the ca rtilage (similar to 3.7 cmH(2)O.s and similar to 2 x 10(4) cmH(2)O, re spectively) were estimated. These results indicate that measures of c and Z(op) or Z(cl) data over these frequencies provide information abo ut the dynamic mechanical properties of both the soft tissue and carti lage in the airway walls.