REPEATED MEASUREMENTS OF AIRWAY AND PARENCHYMAL MECHANICS IN RATS BY USING LOW-FREQUENCY OSCILLATIONS

For studies investigating the mechanisms underlying the development of allergic conditions such as asthma, noninvasive methodologies for sep arating airway and parenchymal mechanics in animal models are required . To develop such a method, seven Brown Norway rats were studied on th ree occasions over a 14-day period. After the baseline measurements, o n the third day inhaled methacholine was administered. Once lung funct ion returned to the baseline level, a thoracotomy was performed to com pare the lung mechanics in the intact-and open-chest conditions. On ea ch occasion, the rats were anesthetized, paralyzed, and intubated. Sma ll-amplitude oscillations between 0.5 and 21 Hz were applied through a wave tube to obtain respiratory impedance (Zrs). Esophageal pressure was measured to separate Zrs into pulmonary (ZL) and chest wall(Zw) co mponents. A model containing a frequency-independent resistance and in ertance and a tissue component, including tissue damping and elastance , was fitted to Zrs, ZL, and Zw spectra. Measurements of Zrs, ZL, or Z w and the model parameters calculated from them did not differ among t ests. The number of animals required to show group changes in lung mec hanics was significantly lower when animals were measured noninvasivel y than when the group changes were calculated from open-chest measurem ents. In conclusion, the method reported in this study can be used to separate airway and lung tissue mechanics noninvasively over a series of tests and can detect pulmonary constrictor responses for the airway s and the parenchyma separately.