Repeated measurements of airway and parenchymal mechanics in rats by using low-frequency oscillations

For studiesinvestigating the mechanisms underlying the development of allergicconditions such as asthma, noninvasive methodologies for separatingairway and parenchymal mechanics in animal models are required. Todevelop such a method, seven Brown Norway rats were studied on threeoccasions over a 14-day period. After the baseline measurements, on thethird day inhaled methacholine was administered. Once lung functionreturned to the baseline level, a thoracotomy was performed to comparethe lung mechanics in the intact- and open-chest conditions. On eachoccasion, the rats were anesthetized, paralyzed, and intubated.Small-amplitude oscillations between 0.5 and 21 Hz were applied througha wave tube to obtain respiratory impedance (Zrs). Esophageal pressurewas measured to separate Zrs into pulmonary(ZL) and chest wall (Zw)components. A model containing a frequency-independent resistance andinertance and a tissue component, including tissue damping andelastance, was fitted to Zrs,ZL, and Zw spectra. Measurementsof Zrs, ZL, or Zw and the modelparameters calculated from them did not differ among tests. The numberof animals required to show group changes in lung mechanics wassignificantly lower when animals were measured noninvasively than whenthe group changes were calculated from open-chestmeasurements. In conclusion, the method reported in thisstudy can be used to separate airway and lung tissue mechanics noninvasively over a series of tests and can detect pulmonary constrictor responses for the airways and the parenchyma separately.