PULMONARY ARTERIAL ELASTICITY IN AWAKE DOGS

We measured the relationship between pulmonary arterial pressure (Ppa) , diameter (D), and length of a segment of the main pulmonary artery ( MPA) in chronically instrumented conscious dop breathing spontaneously (CCC). There were no physiologically significant changes in Ppa or D in the CCC dogs postoperatively, and the cross-sectional MPA shape mea sured by fast computed tomography was nearly circular. These results s uggest that the MPA was not distorted by chronic instrumentation. We c ompared measurements made in the CCC dogs with previous measurements i n acutely instrumented anesthetized dogs with open chests (AAO). The e lasticity of MPA in the CCC animals was frequency dependent between 1 and 14 Hz and was similar to that in the AAO dogs. Oscillations of D p receded Ppa at cardiac frequencies in the AAO animals, but the D and P pa oscillations were in phase in the CCC animals. The oscillations of length relative to D were significantly less in the CCC than in the AA O dogs. We conclude that, with limitations, the hemodynamic properties of the MPA can be measured in the CCC subjects. We suggest that the d iscrepancies between the AAO and CCC dogs can be attributed to differe nces in extrinsic loading of the MPA.