Determination of airway and tissue resistances after antigen and methacholine in nonhuman primates.

Antigen challenge of Ascaris suum-sensitive animals has been used as a model of asthma in humans. However, no reports have separated total respiratory resistance into airway (Raw) and tissue (Rti) components. We compared input impedance (Zin) and transfer impedance (Ztr) to determine Raw and Rti in anesthetized cynomolgus monkeys under control and bronchoconstricted conditions. Zin data between 1 and 64 Hz are frequency dependent during baseline conditions, and this frequency dependence shifts in response to A. suum or methacholine. Thus it cannot be modeled with the DuBois model, and estimates of Raw and Rti cannot be determined. With Ztr, baseline data were much less variable than Zin in all monkeys. After bronchial challenge with A. suum or methacholine, the absolute amplitude of the resistive component of Ztr increased and its zero crossing shifted to higher frequencies. These data can estimate Raw and Rti with the six-element DuBois model. Therefore, in monkeys, Ztr has advantages over other measures of lung function, since it provides a methodology to separate estimates of Raw and Rti. In conclusion, Ztr shows spectral features similar to those reported in healthy and asthmatic humans.