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1 Department of Hydraulics Laboratory, Institute Biomedical Technology, Ghent University, Gent, Belgium
2 Department of Hemodynamic Research Center, University of Liege, Liege, Belgium
3 Department of Centre for Experimental Surgery and Anaesthesiology, Katholieke Universiteit Leuven, Leuven, Belgium
* To whom correspondence should be addressed. E-mail: patrick.segers{at}rug.ac.be.
Maximal left ventricular (LV) hydraulic power output (PWRmax), corrected for preload (Ved: end-diastolic volume) as PWRmax/Ved
is an index of left ventricular (LV) contractility. While preload-adjusted maximal power (PAMP) is usually calculated with =2, there is uncertainty about the optimal value of (= 1 for normal and 2 for dilated LV). The aim of this work is to study the determining factors of . The data set consisted of 245 recordings (steady state and vena cava occlusion) in 10 animals in an ischemic heart pig model. The occlusion data yielded: (i) the slope (Ees; 2.01±0.77 mmHg/ml; 0.71-4.16 mmHg/ml) and intercept (V0; -11.9±22.6 ml; -76 to 39 ml) of the end-systolic PV relation; (ii) the optimal -factor (assessed by fitting an exponential curve through the Ved-PWRmax relation) was 1.94±0.88 (0.29 to 4.73). The relation of with Ved was weak ( = 0.60+0.02 Ved ;r2=0.20) . In contrast, we found an excellent exponential relation between V0 and ( =2.16e 0.0189V0; r2 = 0.70). PAMP, calculated from the steady state data, was 0.64±0.40 mWatt/ml2 (range 0.14-2.83) with a poor correlation with Ees (r=0.30; P<0.001). An alternative formulation of PAMP as PWRmax/(Ved--V0)2, incorporating V0, yielded 0.47±0.26 mWatt/ml2 (range 0.09-1.42) and was highly correlated with Ees (r=0.89; P<0.001). In conclusion, correct preload-adjustment of maximal LV power requires incorporation of V0 and thus of data measured under altered loading conditions.
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