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

Steady-state wave intensity (WI) analysis indicates that characteristic midsystolic falls in fetal pulmonary trunk (PT) and artery (PA) blood flow are due to an extremely large backward-running compression wave ([BCW.sub.ms]) that 1) originates from the pulmonary microvasculature by a combination of cyclical pulmonary vasoconstriction and vascular reflection of the forward-running compression wave ([FCW.sub.is]) associated with impulsive right ventricular ejection, and 2) is transmitted into the PT. However, no information is available about the dynamic properties of PA [BCW.sub.ms] 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 [BCW.sub.ms], and its associated P and U changes ([DELTA]P and [DELTA]U, respectively), were similar to those of [FCW.sub.is]. The PA [FCW.sub.is] and [BCW.sub.ms], and their accompanying [DELTA]P and [DELTA]U, were all transiently potentiated after an ES. Beat-by-beat PA [FCW.sub.is]-[BCW.sub.ms] wave area, [DELTA]P and [DELTA]U relationships were highly linear ([R.sup.2] [greater than or equal to] 0.91) with slopes of 1.36-1.47 (P < 0.001), consistent with the presence of a vasoconstrictor component in PA [BCW.sub.ms]. PA-PT [BCW.sub.ms] area and [DELTA]P and [DELTA]U relationships were also linear ([R.sup.2] [greater than or equal to] 0.77) with slopes of 0.23-0.64 (P < 0.001). These results indicate that the fetal PA [BCW.sub.ms] contributes to beat-to-beat regulation of not only PA but also PT hemodynamics. fetal pulmonary blood flow; fetal pulmonary blood pressure; postextrasystolic potentiation