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Single-beat determination of preload recruitable stroke work relationship: derivation and evaluation in conscious dogs

^a Victor Chang Cardiac Research Institute and Cardiology Department, St. Vincent’s Hospital, Sydney, Australia

View larger version (38K): [in a new window]   Figure 1 Left panel: Diagram illustrating the placements of the base-apex (dimension a) and anterior-posterior (dimension b) ultrasound dimension transducers, LV micromanometer (LVP) and the pneumatic occluders around the inferior vena cava (IVCO) and descending aorta (AO). Right panel: Schematic diagram of the derived epicardial left ventricular end-diastolic volume (EDVepi), which includes the left ventricular wall volume (LVwall). LV = left ventricle.

View larger version (36K): [in a new window]   Figure 2 An example of the global and regional PRSW relationships derived from a series of LV pressure-volume loops recorded during a single vena caval occlusion. The global PRSW relationship is the relationship between stroke work, calculated as the pressure-volume loop area (shaded for one beat) and the corresponding end-diastolic volume for the same beat. Mw and Vw are the slope and volume-axis intercept, respectively, of the global PRSW relationship. Regional PRSW relationships are the relationships between regional stroke work (calculated as the pressure-dimension loop area formed by plotting LV pressure against the regional dimension) and the corresponding end-diastolic length of the base-apex or anterior-posterior dimension. aw and bw are the corresponding dimension-axis intercepts. LV = left ventricle; Mw = slope of the PRSW relationship; PRSW = preload recruitable stroke work; Vw = volume-axis intercept of the PRSW relationship.

View larger version (14K): [in a new window]   Figure 3 Top panel: Relationship between stroke work calculated as the product of stroke volume and mean ejection pressure and stroke work calculated as pressure-volume loop area based on the same beats from Group I dogs displayed in the middle panel. Middle panel: Relationship between single beat Mw (SBMw) estimates and multibeat Mw measurements in Group I. Multibeat data were obtained during vena caval occlusions performed before and during aortic constriction. Single beat estimates were made from the first steady-state beat preceding each vena caval occlusion. The relationships were not significantly different from the line of identity, whether based on individual measured k values (SBMw,measured, open circles) or calculated assuming k to be constant at 0.7 (SBMw,calculated, closed circles). Bottom panel: Bland-Altman analysis (25) of the same calculated SBMw and multibeat Mw values: the difference between multibeat Mw and SBMw values is plotted against their average. Mw = slope of the PRSW relationship.

View larger version (21K): [in a new window]   Figure 4 Relationship between beat-to-beat single-beat Mw (SBMw) (top panel) maximum power divided by the square of the end-diastolic volume (PWRmax/EDV2) (middle panel) or single-beat elastance (SBEes) (bottom panel) and end-diastolic volume during the same vena caval occlusion runs performed before (control) and during aortic constriction. End-diastolic volumes are normalized to the value of the first steady-state beat recorded. Values of the three single-beat indexes are normalized to the control steady-state value. Single-beat Mw estimates are insensitive to both preload and afterload. PWRmax/EDV2 is significantly preload sensitive (p < 0.05) but is significantly afterload sensitive only for EDVs less than 65% of baseline (*p < 0.05). Single-beat Ees is highly variable from beat to beat.

View larger version (28K): [in a new window]   Figure 5 Top panel: The effects of aortic constriction on the mean multibeat PRSW measurements (Vw and Mw) and single-beat Mw (SBMw) estimates in Group II dogs. Neither multibeat nor single-beat estimates are sensitive to the increased afterload. There were no significant differences between multibeat and single beat Mw values, whether based on individual k values (measured) or a constant k value of 0.7 (calculated). Bottom panel: The corresponding volume-axis intercept (Vo) and slope (Ees) of the ESPVR, single-beat Ees (SBEes) and PWRmax/EDV2 data (see text). ESPVR = end-systolic pressure-volume relationship; Mw = slope of the PRSW relationship; PRSW = preload recruitable stroke work; PWRmax/EDV2 = maximum left ventricular power divided by the square of end-diastolic volume. Vw = volume-axis intercept of the PRSW relationship. *p < 0.05 vs. control.

View larger version (29K): [in a new window]   Figure 6 Top panel: The effects of calcium infusion on the mean multibeat and single-beat PRSW estimates in Group II dogs. Both multibeat and single-beat Mw are sensitive to the inotropic stimulation. There were no significant differences between multibeat and single-beat Mw values. Bottom panel: The corresponding ESPVR (Vo and Ees), single-beat Ees and PWRmax/EDV2 data (see text). Ees = slope of the ESPVR; Mw = slope of the PRSW relationship; PWRmax/EDV2 = maximum left ventricular power divided by the square of end-diastolic volume; Vo = volume-axis intercept of the ESPVR; Vw = volume-axis intercept of the PRSW relationship. *p < 0.05 vs. control.

View larger version (13K): [in a new window]   Figure 7 The measured Vw,epi/EDVB,epi ratios in all 12 dogs in Groups I and II plotted against the individual body weights of the dogs. The regression line and 95% confidence intervals of the regression are shown: no relationship is evident. Vw,epi = the volume within the epicardial shell corresponding to the volume axis intercept of the PRSW relationship; EDVB,epi = the volume within the epicardial shell corresponding to the baseline, steady-state end-diastolic volume.

View larger version (17K): [in a new window]   Figure 8 Top panel: Relationship between single-beat Mw (SBMw) estimates and multibeat Mw measurements in Group II. Multibeat data were obtained during vena caval occlusions performed before and during aortic constriction and calcium infusion. The relationships were not significantly different from the line of identity, whether based on individual measured k values (SBMw,measured) or calculated assuming k to be constant at 0.7 (SBMw,calculated). Bottom panel: Corresponding relationships between single-beat elastance (SBEes) or PWRmax/EDV2 and multibeat elastance (Ees). Both single-beat indexes correlated very poorly with multibeat Ees. Mw = slope of the PRSW relationship; PWRmax/EDV2 = maximum left ventricular power divided by the square of end-diastolic volume.