A COMPARATIVE-STUDY OF ELASTIC PROPERTIES OF RAT AND GUINEA-PIG PARENCHYMAL STRIPS

Constricted guinea pig (CP) airways are much less sensitive to changes in transpulmonary pressure (Ptp) than are those of the rat. The objec t of this study was to investigate whether differences in the mechanic al behavior of the lung parenchyma could explain differences between t he two species in the interdependence of the airway and parenchyma. Su bpleural lung strips from guinea pigs and rats were excised and suspen ded in an organ bath. One end of each strip was attached to a force tr ansducer and the other to a servo-controlled lever arm that effected l ength (L) changes in the strip. Sinusoidal oscillations at varying fre quencies and amplitudes were applied at different resting tensions. Me asurements of L and resting tension (T) were recorded during baseline conditions and after acetylcholine (ACh) challenge. Elastance (E) and resistance (R) were calculated by fitting changes in T and L to the eq uation of motion. During sinusoidal oscillations, E and R in the two s pecies were different in both the unconstricted and constricted states . The effect of T on E was significantly different in rats and GPs; E was less dependent on T in GPs. Insofar as E is a measure of the load against which airway smooth muscle (ASM) contracts, this difference ma y represent a potential mechanism to explain why constricted CP airway s are less sensitive to changes in Ptp.