Dynamic characterization and hemodynamic effects of pulmonary waves in fetal lambs using cardiac extrasystoles and beat-by-beat wave intensity analysis

Smolich JJ, Mynard JP, Penny DJ. Dynamic characterization and hemodynamic effects of pulmonary waves in fetal lambs using cardiac extrasystoles and beat-by-beat wave intensity analysis. Am J Physiol Regul Integr Comp Physiol 297: R428-R436, 2009. First published June 3, 2009; doi:10.1152/ajpregu.00174.2009.-Steady-state wave intensity (WI) analysis indicates that characteristic mid-systolic falls in fetal pulmonary trunk (PT) and artery (PA) blood flow are due to an extremely large backward-running compression wave (BCWms) that 1) originates from the pulmonary microvasculature by a combination of cyclical pulmonary vasoconstriction and vascular reflection of the forward-running compression wave (FCWis) associated with impulsive right ventricular ejection, and 2) is transmitted into the PT. However, no information is available about the dynamic properties of PA BCWms and its contribution to beat-to-beat regulation of pulmonary hemodynamics. Accordingly, beat-by-beat WI analysis was performed during brief increases in ventricular contractility accompanying an extrasystole (ES) in nine anesthetized late-gestation fetal sheep instrumented with PT and left PA micromanometer catheters to measure pressure (P) and transit-time flow probes to obtain blood velocity (U). WI was calculated as the product of P and U rates of change. At steady state, the magnitude of PA BCWms, and its associated P and U changes (Delta P and Delta U, respectively), were similar to those of FCWis. The PA FCWis and BCWms, and their accompanying Delta P and Delta U, were all transiently potentiated after an ES. Beat-by-beat PA FCWis-BCWms wave area, Delta P and Delta U relationships were highly linear (R-2 >= 0.91) with slopes of 1.36-1.47 (P < 0.001), consistent with the presence of a vasoconstrictor component in PA BCWms. PA-PT BCWms area and Delta P and Delta U relationships were also linear (R-2 >= 0.77) with slopes of 0.23-0.64 (P < 0.001). These results indicate that the fetal PA BCWms contributes to beat-to-beat regulation of not only PA but also PT hemodynamics.