title: Extent of load-independence of pressure-normalized stress in swine.
abstract: 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.
authors.affiliation: Department of Biomedical Engineering, Indiana University - Purdue University Indianapolis, IN 46202, USA.
authors.forename: Xinwei
authors.initials: X
authors.lastname: Jia
authors.forename: Jenny S
authors.initials: JS
authors.lastname: Choy
authors.forename: Zhen-Du
authors.initials: ZD
authors.lastname: Zhang
authors.forename: Mark
authors.initials: M
authors.lastname: Svendsen
authors.forename: Liang
authors.initials: L
authors.lastname: Zhong
authors.forename: Ru S
authors.initials: RS
authors.lastname: Tan
authors.forename: Ghassan S
authors.initials: GS
authors.lastname: Kassab
mesh_terms: D000818:Animals; D004280:Dobutamine / Q000008:administration & dosage / Q000494:pharmacology; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D007262:Infusions, Intravenous; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D011312:Pressure; D013312:Stress, Physiological / Q000187:drug effects; D034421:Sus scrofa
chemical_list: D004280:Dobutamine
keywords: afterload; cardiac function; cardiac mechanics; preload; wall stress