Relationship of Hydraulic Impedance and Elasticity in the Pulmonary Artery of Maturing Newborn Pigs

Abstract

The current study determined the dynamic stress–strain elastic moduli (EY) and characteristic impedances (Z0(2–7Hz)) of the main pulmonary artery in open-chest, anesthetized newborn pigs at 2 days, 2 weeks, and 3 months of age. EY and Z0(2–7Hz) were compared to those values derived from the Womersley and Moens–Korteweg equations (denoted EW-MK and Z0W-MK, respectively) to test the validity of these equations in describing the elasticity of the intact newborn pulmonary artery. EY was defined as the ratio of stress to strain. The current study hypothesized that: (1) EY and EW-MK are numerically similar, and therefore the Womersley and Moens–Korteweg equations accurately describe the viscoelastic properties of the main pulmonary artery of the newborn pig, and (2) that both EY and Z0 are elevated at birth and undergo a steady decline with maturation. EY was not significantly different from EW-MK, while Z0(2–7Hz) was nearly identical to Z0W-MK in all groups. The elastic modulus peaked (P < 0.001) in 2-week-old pigs compared with both younger and older animals, while Z0(2–7Hz) decreased with increasing age (48 h = 1237 ± 251 [SEM] dyn s cm−5, 2-week = 433 ± 95 dyn s cm−5, 3 month = 162 ± 17 dyn s cm−5, P < 0.001). These experiments validate the Womersley and Moens–Korteweg equations as accurately describing the elastic properties of the intact newborn pig pulmonary artery. These data also demonstrate that a diminution in Z0 may occur even with increased wall stiffness, as observed in our 2-week-old pigs.