A distensible vessel model applied to hypoxic pulmonary vasoconstriction in the neonatal pig

Recently, we presented a simple two-parameter distensible vessel model as a potential tool for characterizing pulmonary vascular pressure vs. flow curves under zone 3 conditions (Linehan et al. J. Appl. Physiol. 73: 987- 994, 1992). One parameter, α, represents the distensibility of the resistance vessels as the fractional change in vessel diameter per Torr change in pressure, and the other parameter, R₀, represents the vascular resistance that would exist if the resistance vessels were at their respective diameters obtained if the vascular pressure were zero. The objective of the present study was to determine whether this distensible vessel model was capable of describing the pressure vs. flow data obtained during hypoxia vasoconstriction and under control conditions in isolated lungs from neonatal pigs. The piglet lungs were perfused with autologous blood, and the pulmonary arterial pressure was measured over a range of flow rates from 15 to 250 ml · min^-1 · kg^-1 at constant left atrial (3 Torr) pressure. The model provided a reasonable fit to the data under both conditions. Hypoxia resulted in a significant increase in R₀, from 0.39 ± 0.10 Torr · ml^-1 · min · kg during control conditions to 1.41 ± 0.46 Torr · ml^-1 · min · kg during hypoxia. α was 2.4 ± 0.4%/Torr under control conditions and 2.0 ± 0.4%/Torr during hypoxia, but this difference was not statistically significant. The results suggest that the distensible vessel model may be useful for interpreting pressure-flow data in terms of changes in geometry and distensibility of the resistance vessels in response to a vasoconstrictor stimulus such as hypoxia.