Ventricular stroke work and efficiency both remain nearly optimal despite altered vascular loading

Area of Science:

• Cardiovascular Physiology
• Biomedical Engineering
• Cardiac Mechanics

Background:

• Clinical and animal studies suggest ventricular-vascular coupling operates at optimal ventricular efficiency (EFF) or stroke work (SW).
• Cardiac dysfunction often compromises efficiency, but distinctions between maximal work and efficiency coupling states are theoretical.
• Limited experimental data exist on optimal conditions for SW and EFF in the same heart.

Purpose of the Study:

• To experimentally define optimal conditions for stroke work and efficiency in the same heart.
• To test if deviations from optimal conditions significantly decrease both parameters.
• To investigate ventricular-vascular coupling dynamics under varying arterial impedance.

Main Methods:

• Studied 10 isolated blood-perfused canine hearts.
• Varied contractility and ejected into a simulated three-element Windkessel model.
• Measured myocardial oxygen consumption and SW across a range of afterload resistances (indexed by Ea/Ees).

Main Results:

• Maximal SW occurred at Ea/Ees = 0.80 ± 0.16; maximal EFF occurred at Ea/Ees = 0.70 ± 0.15 (P < 0.01).
• Differences in optimal Ea/Ees ratios for SW and EFF were small.
• Both SW and EFF remained ≥90% of their optima over a broad overlapping range of Ea/Ees ratios (0.3–1.3).

Conclusions:

• Ventricular-vascular coupling maintains near-maximal stroke work and efficiency under many conditions.
• The heart operates efficiently across a wide spectrum of ventricular-vascular interactions.
• These findings challenge the notion of strict optimality for SW or EFF, highlighting functional resilience.