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Preload-adjusted right ventricular maximal power: concept and validation

Soren Schenk,¹ Zoran B. Popovi,² Yoshie Ochiai,¹ Fernando Casas,¹ Patrick M. McCarthy,^1,3 Randall C. Starling,² Michael W. Kopcak, Jr.,¹ Raymond Dessoffy,¹ Jose L. Navia,³ Neil L. Greenberg,² James D. Thomas,² and Kiyotaka Fukamachi¹

¹Department of Biomedical Engineering, ²Department of Cardiovascular Medicine, ³Department of Thoracic and Cardiovascular Surgery, The Cleveland Clinic Foundation, Cleveland, Ohio 44195

Submitted 4 February 2004 ; accepted in final form 7 May 2004

Right ventricular (RV) maximal power (PWR_mx) is dependent on preload. The objective of this study was to test our hypothesis that the PWR_mx versus end-diastolic volume (EDV) relationship, analogous to the load-independent stroke work (SW) versus EDV relationship (preload-recruitable SW, PRSW), is linear, with the PWR x-axis intercept (V_0PWR) corresponding to the PRSW intercept (V_0SW). If our hypothesis is correct, the preload sensitivity of PWR_mx could be eliminated by adjusting for EDV and V_0PWR. Ten dogs were instrumented with a pulmonary flow probe, micromanometers, and RV conductance catheter. Data were obtained during bicaval occlusions under various conditions and fitted to PWR_mx = a·(EDV – V_0PWR), where a is the slope of the relationship. The PWR_mx versus EDV relationship did not deviate from linearity ( = 1.09, P = not significant vs. 1), and V_0PWR correlated with V_0SW (r = 0.93, P <0.0001). V_0PRW was related to steady-state EDV and left ventricular end-diastolic pressure, allowing for estimation of V_0PWR (V_0Est) and single-beat PWR_mx preload adjustment. Dividing PWR_mx by the difference of EDV and V_0PWR (PAMP_V0PWR) eliminated preload dependency down to 50% of the baseline EDV. PWR_mx adjustment using V_0Est (PAMP_V0Est) showed similar preload independency. Enhancing contractility increased PAMP_V0PWR and PAMP_V0Est from 176 ± 52 to 394 ± 205 W/ml x 10⁴ and 145 ± 51 to 404 ± 261 W/ml x 10⁴, respectively, accompanied by an increase of PRSW from 13.0 ± 4.5 to 29.7 ± 16.4 mmHg (all P <0.01). PAMP_V0PWR and PAMP_V0Est correlated with PRSW (r = 0.85; r = 0.77; both P <0.001). Numerical modeling confirmed the accuracy of our experimental data. Thus preload adjustment of PWR_mx should consider a linear PWR_mx versus EDV relationship with distinct V_0PWR. PAMP_V0PWR is a preload-independent estimate of RV contractility that may eventually be determined noninvasively.

hemodynamics; contractility; right ventricle

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