Department of Biomedical Engineering, Indiana University - Purdue University Indianapolis, IN 46202, USA.
Exp Biol Med (Maywood). 2013 Jul;238(7):821-9. doi: 10.1177/1535370213494548. Epub 2013 Jul 4.
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 dσ*/dtmax (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, dσ*/dt 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, dσ*/dt 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, dσ*/dtmax did not change significantly (6.72 ± 1.18 s⁻¹ vs 6.89 ± 1.28 s⁻¹, P = NS). As expected, dσ*/dtmax was significantly increased with dobutamine. A linear regression showed no correlation between dσ*/dtmax and preload (r² = 0.02, P = 0.17) within a maximum range of -30% to +50% of preload change, or between dσ*/dtmax and afterload (r² = 0.03, P = 0.36) within maximum range of 0-100% of afterload increase, respectively. In conclusion, dσ*/dtmax 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.
心肌收缩力的无负荷指数提供了一种心脏功能的测量方法。以前的收缩力指数要么是负荷依赖性的，要么是有创的。我们试图确定 dσ*/dtmax（σ* 是压力归一化的应力）与其他公认的指数相比，在多大程度上不受负荷（前负荷和后负荷）的影响。六只麻醉猪在各种负荷条件下进行左心室压力-容积测量。平均前负荷降低了 70.0±15.0%（从 39.2±6.4 毫升降至 11.7±7.7 毫升），增加了 49.3±5.9%（从 35.1±7.4 毫升增至 51.7±8.9 毫升）。平均后负荷增加了 74.3±43.5%（从 3.3±0.6 mmHg/mL 增至 5.7±1.7 mmHg/mL）。当使用下腔静脉阻塞在平均 21.7%（39.2±6.4 毫升降至 30.7±6.2 毫升）范围内降低前负荷时，dσ*/dtmax 没有显著变化（6.50±1.10 s⁻¹ vs 6.60±0.90 s⁻¹，P=非显著[NS]）。当从生理盐水输注中平均增加 29.3%（35.1±7.4 毫升至 45.4±7.3 毫升）的前负荷时，dσ*/dtmax 没有显著变化（7.04±1.00 s⁻¹ vs 7.29±1.10 s⁻¹，P=NS）。当使用主动脉内球囊闭塞平均增加 42.4%（3.3±0.6 mmHg/mL 至 4.7±1.0 mmHg/mL）的后负荷时，dσ*/dtmax 没有显著变化（6.72±1.18 s⁻¹ vs 6.89±1.28 s⁻¹，P=NS）。如预期的那样，dσ*/dtmax 随着多巴酚丁胺的输注而显著增加。线性回归显示，dσ*/dtmax 与前负荷之间没有相关性（r²=0.02，P=0.17），在前负荷变化的最大范围为-30%至+50%，或与后负荷之间没有相关性（r²=0.03，P=0.36），在后负荷增加的最大范围为 0%至 100%。总之，dσ*/dtmax 在平均前负荷降低 21.7%、前负荷增加 29.3%、后负荷增加 42.4%的情况下不受负荷条件的影响，并且对多巴酚丁胺输注敏感。
