In the pulmonary circulation, resistive and compliant properties
overlap in the same vessels. Resistance varies nonlinearly with
pressure and flow; this relationship is driven by the elastic
properties of the vessels. Linehan et al. (1982) correlated the
mean pulmonary arterial pressure and mean flow with resistance
using an original equation incorporating the distensibility of the
pulmonary arteries. The goal of this study was to validate this
equation in an in vivo porcine model. In vivo measurements were
acquired in 6 pigs. The distensibility coefficient (DC) was
measured by placing piezo-electric crystals around the pulmonary
artery (PA). In addition to experiments under pulsatile conditions,
a right ventricular (RV) bypass system was used to induce
a continuous pulmonary flow state. The Linehan's equation was
then used to predict the pressure from the flow under continuous
flow conditions. The diameter-derived DC was 2.4 %/mmHg
(±0.4 %), whereas the surface area-based DC was 4.1 %/mmHg
(±0.1 %). An increase in continuous flow was associated with
a constant decrease in resistance, which correlated with the
diameter-based DC (r=-0.8407, p=0.044) and the surface areabased DC (r=-0.8986, p=0.028). In contrast to the Linehan’s
equation, our results showed constant or even decreasing
pressure as flow increased. Using a model of continuous
pulmonary flow induced by an RV assist system, pulmonary
pressure could not be predicted based on the flow using the
Linehan’s equation. Measurements of distensibility based on the
diameter of the PA were inversely correlated with the resistance.