RELATIONSHIP BETWEEN HETEROGENEOUS CHANGES IN AIRWAY MORPHOMETRY AND LUNG RESISTANCE AND ELASTANCE

We present a dog lung model to predict the relation between inhomogene ous changes in airway morphometry and lung resistance (RL) and elastan ce (EL) for frequencies surrounding typical breathing rates. The RL an d EL were sensitive in distinct ways to two forms of peripheral constr iction. First, when there is a large and homogeneous constriction, the RL increases uniformly over the frequency range. The EL is rather una ffected below 1 Hz but then increases with frequencies up to 5 Hz. Thi s increase is caused by central airway wall shunting. Second, the RL a nd EL are extremely sensitive to mild inhomogeneous constriction in wh ich a few highly constricted or nearly closed airways occur randomly t hroughout the periphery. This results in extreme increases in the leve ls and frequency dependence of RL and EL but predominantly at typical breathing rates (<1 Hz). Conversely, the RL and EL are insensitive to highly inhomogeneous airway constriction that does not produce any nea rly closed airways. Similarly, alterations in the RL and EL due to cen tral airway wall shunting are not likely until the preponderance of th e periphery constricts substantially. The RL and EL spectra are far mo re sensitive to these two forms of peripheral constriction than to con striction conditions known to occur in the central airways. On the bas is of these simulations, we derived a set of qualitative criteria to i nfer airway constriction conditions from RL and EL spectra.