ELASTIC ENERGY AS AN INDEX OF RIGHT-VENTRICULAR FILLING

Background: Right ventricle (RV) preload assessment remains controvers ial because the complexity of RV geometry is an obstacle to wall stres s modeling. We developed a method to evaluate end-diastolic RV elastic energy (EL), a variable that integrates all the stretching effects of venous return and that can be easily estimated at the bedside from th e area under the diastolic RV pressure-volume curve. The purpose of th is study was to compare the clinical utility of EL and of the two conv entional variables used to assess RV filling; ie, right atrial pressur e (Pra) and RV end-diastolic volume (EDV). Method: We studied 26 posto perative patients who required a rapid fluid challenge. Energetics wer e evaluated by constructing the RV pressure-volume loop at the bedside using right heart catheterization with RV ejection fraction (EF) deri vation. Correlations between RV filling and RV performance (ejection a nd mechanical efficiency) were studied. RV filling indexes were Pra, E DV, and EL. Indexes of RV ejection were stroke volume (SV), RV stroke work (RVSW), mechanical energy expenditure during ejection (EM), and t otal energy expenditure of contraction (ET). Indexes of RV mechanical efficiency were EF and the EM/ET ratio. Results: Three important resul ts were obtained, First, among RT? ejection indexes, those that correl ated best with RV filling indexes were ER;I and ET. Second, we found s ignificant linear relationships between improved RV filling, as assess ed by changes in EDV and EL, and improved RV ejection, as assessed by changes in SV, RVSW, EM, or ET. Third, changes in EDV and EL also pred icted improved mechanical efficiency, as assessed by changes in EF and EM/ET. In all situations, changes in EL yielded the strongest correla tions. Conclusions: Derivation of EL is simple and appears to be the b est clinical means of assessing Starling's law of the heart for the RV .