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.