The contractility index d σ*/d t max was independent of loading conditions within an average of 21.7% preload decrease, 29.3% preload increase, and 42.4% afterload increase, but sensitive to dobutamine.
The contractility index d σ*/d t max is independent of loading conditions within specific ranges of preload and afterload changes in a swine model.
valor p: p=NS
A load-independent index of myocardial contractility provides a measure of cardiac function. Previous contractility indices have been shown to be either load-dependent or invasive. We sought to determine the extent of load (preload and afterload)-independence of d σ*/d t max ( σ* is pressure-normalized stress) in comparison with other well-established indices. Six anaesthetized pigs underwent left ventricular pressure–volume measurements under various load conditions. The average preload was decreased by 70.0 ± 15.0% (from 39.2 ± 6.4 mL to 11.7 ± 7.7 mL) and increased by 49.3 ± 5.9% (from 35.1 ± 7.4 mL to 51.7 ± 8.9 mL). The average afterload was increased by 74.3 ± 43.5% (from 3.3 ± 0.6 mmHg/mL to 5.7 ± 1.7 mmHg/mL). When preload was reduced within an average of 21.7% (39.2 ± 6.4 mL to 30.7 ± 6.2 mL) using occlusion of the inferior vena cava, d σ*/d t max did not change significantly (6.50 ± 1.10 s −1 vs 6.60 ± 0.90 s −1 , P = non-significant NS). When preload was increased within an average of 29.3% (35.1 ± 7.4 mL to 45.4 ± 7.3 mL) from infusion of normal saline, d σ*/d t max did not change significantly (7.04 ± 1.00 s −1 vs 7.29 ± 1.10 s −1 , P = NS). When afterload was increased within an average of 42.4% (3.3 ± 0.6 mmHg/mL to 4.7 ± 1.0 mmHg/mL) using intra-aortic balloon occlusion, d σ*/d t max did not change significantly (6.72 ± 1.18 s −1 vs 6.89 ± 1.28 s −1 , P = NS). As expected, d σ*/d t max was significantly increased with dobutamine. A linear regression showed no correlation between d σ*/d t max and preload ( r 2 = 0.02, P = 0.17) within a maximum range of −30% to +50% of preload change, or between d σ*/d t max and afterload ( r 2 = 0.03, P = 0.36) within maximum range of 0–100% of afterload increase, respectively. In conclusion, d σ*/d t max is independent of loading conditions within an average of 21.7% of preload decrease, 29.3% of preload increase, 42.4% of afterload increase, and sensitive to dobutamine infusion.
Jia et al. (Mon,) conducted a other in Myocardial contractility assessment (n=6). Alteration of loading conditions (preload and afterload) and dobutamine vs. Baseline loading conditions was evaluated on Extent of load-independence of d σ*/d t max (pressure-normalized stress) (p=NS). The contractility index d σ*/d t max was independent of loading conditions within an average of 21.7% preload decrease, 29.3% preload increase, and 42.4% afterload increase, but sensitive to dobutamine.