Capillary pressure estimates from arterial and venous occlusion in intact dog lung.

We performed pulmonary venous occlusions in order to check the validity of the pulmonary capillary pressure measurements obtained using pulmonary arterial occlusion in the intact animal. The venous and arterial postocclusion pressure profiles were recorded using balloon catheters introduced, respectively, into a left lower lobe vein and into a right pulmonary artery in the anaesthetized open-chest dog. The pressure profiles were fitted by a biexponential function with an early exponential and a late exponential presenting, respectively, a short and a long time constant. We used the zero-time extrapolation of the late slow exponential to obtain an arterial (Pc,ao) and a venous (Pc,vo) estimate of the pulmonary capillary pressure. Each Pc,ao and Pc,vo made it possible to calculate a fractional arterial or venous pressure gradient when referenced to the arteriovenous pressure gradient measured during the occlusion process. In nine dogs, when referenced to the whole lung, the arterial, middle and venous fractional pressure gradients were 37 +/- 11, 10 +/- 6, and 53 +/- 12%, respectively. As the middle fractional pressure gradient is low, we conclude that pulmonary capillary pressure estimates from arterial occlusion are close to the venous occlusion estimates of capillary pressure in the intact dog lung.