Relationship of hydraulic impedance and elasticity in the pulmonary arteryof maturing newborn pigs

The current study determined the dynamic stress-strain elastic moduli (E-Y) and characteristic impedances (Z(0(2-7Hz))) of the main pulmonary artery i n open-chest, anesthetized newborn pigs at 2 days, 2 weeks, and 3 months of age. E-Y and Z(0(2-7Hz)) were compared to those values derived from the Wo mersley and Moens-Korteweg equations (denoted EW-MK and Z(0W-MK), respectiv ely) to test the validity of these equations in describing the elasticity o f the intact newborn pulmonary artery. Ey was defined as the ratio of stres s to strain. The current study hypothesized that: (1) E-Y and EW-MK are num erically similar, and therefore the Womersley and Moens-Korteweg equations accurately describe the viscoelastic properties of the main pulmonary arter y of the newborn pig, and (2) that both E-Y and Z(0) are elevated at birth and undergo a steady decline with maturation. Ey was not significantly diff erent from EW-MK while Z(0(2-7Hz)) was nearly identical to Z(0W-MK) in all groups. The elastic modulus peaked (P < 0.001) in 2-week-old pigs compared with both younger and older animals, while Z(0(2-7Hz)) decreased with incre asing 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 describin g the elastic properties of the intact newborn pig pulmonary artery. These data also demonstrate that a diminution in Z(0) may occur even with increas ed wall stiffness, as observed in our 2-week-old pigs. (C) 2001 Academic Pr ess.