Spectral characterization of pulmonary arterial elasticity in dogs

Pulmonary arterial elasticity (in terms of the pressure-strain modulus E_p) was calculated from pressure and diameter measurements of the main pulmonary artery (MPA) in seven open-chested dogs under chloralose anesthesia. Pressure and diameter data were obtained with a micromanometer tipped catheter and sonomicrometry respectively at 3 levels of positive end-expiratory pressure (PEEP). The data were subjected to autoregressive spectral analysis to explore the behavior of the pulmonary arterial elasticity as a function of frequency. The results show that the elasticity of the MPA is frequency dependent. The value of the pulmonary arterial elastic modulus at respiratory frequency became larger with increased levels of PEEP. In contrast, there was no significant increase of E_p at cardiac frequency as PEEP increased. At a frequency ten times the cardiac frequency E_p shows a significant increase in value as a function of PEEP only for the largest imposed PEEP. Furthermore, a comparison of the elastic moduli was made with in vitro data available in the literature. The results suggest that the behavior of E_p in vivo is significantly different then its behavior which was obtained from in vitro studies.