Submitted on July 10, 2007
Accepted on April 16, 2008
Effective arterial elastance as an index of pulmonary vascular load
Philippe Morimont1*, Bernard Lambermont1, Alexandre Ghuysen2, Paul Gerard3, Philippe H Kolh4, Patrizio Lancellotti5, Vincent Tchana-Sato4, Thomas Desaive6, and Vincent D'Orio2
1 Medical Intensive Care, University Hospital of Liege, Liege, Belgium
2 Emergency, University Hospital of Liege, Liege, Belgium
3 Statistics Institute, University of Liege, Belgium
4 Cardiothoracic Surgery, University Hospital of Liege, Liege, Belgium
5 Cardiology, University Hospital of Liege, Belgium
6 Institute of Physics, University of Liege, Liege, Liege, Belgium
* To whom correspondence should be addressed. E-mail: ph.morimont{at}chu.ulg.ac.be.
The aim of this study was to test whether the simple ratio of right ventricular (RV) end-systolic pressure to stroke volume, known as the effective arterial elastance (Ea), provides a valid assessment of pulmonary arterial load in case of pulmonary embolism- or endotoxin-induced pulmonary hypertension. Ventricular pressure-volume data (obtained with conductance catheters) and invasive pulmonary artery pressure and flow waveforms were simultaneously recorded in 2 groups of 6 pure pietran pigs submitted either to pulmonary embolism (group A) or endotoxic shock (group B). Measurements were obtained at baseline, and each 30 minutes after injection of autologous blood clots (0.3 g/kg) in the superior vena cava in group A and after endotoxin infusion in group B. Two methods of calculation of pulmonary arterial load were compared. On one hand, Ea provided by using three-element windkessel model of the pulmonary arterial system [Ea(WK)] was referred to as standard computation. On the other hand, similarly to the systemic circulation, Ea was assessed as the ratio of RV end-systolic pressure to stroke volume [Ea(PV) = Pes/SV]. In both groups, although the correlation between Ea(PV) and Ea(WK) was excellent over a broad range of altered conditions, Ea(PV) systematically overestimated Ea(WK). This offset disappeared when left atrial pressure (Pla) was incorporated into Ea [Ea*(PV) = (Pes-Pla)/SV]. Thus, Ea*(PV), defined as the ratio of RV end-systolic pressure - minus left atrial pressure - to stroke volume, provides a convenient, useful and simple method to assess the pulmonary arterial load and its impact on the RV function.
