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Assessment of Cardiac Function and Energetics in Isolated Mouse Hearts Using 31P NMR Spectroscopy

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Energy conversion efficiency in human left ventricle.

T Kameyama¹, H Asanoi, S Ishizaka

¹Second Department of Internal Medicine, Toyama Medical and Pharmaceutical University, Japan.

|March 1, 1992

Summary

Left ventricular mechanical efficiency remains stable despite changes in heart function, as long as contractility is not severely impaired. This study clarifies why mechanical efficiency is insensitive to pump performance changes.

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Area of Science:

Cardiovascular Physiology
Cardiac Mechanics
Heart Failure Research

Background:

Left ventricular mechanical efficiency is a key indicator of cardiac pump performance.
Previous studies noted mechanical efficiency is surprisingly stable even in heart failure.
The insensitivity of mechanical efficiency to pump performance changes requires further investigation.

Purpose of the Study:

To analyze human left ventricular mechanical efficiency using the pressure-volume area (PVA) concept.
To clarify the reasons behind the observed insensitivity of mechanical efficiency to altered pump performance.
To investigate the relationship between myocardial oxygen consumption (MVO2), PVA, and external work.

Main Methods:

Determined MVO2-PVA relationships and external work in 11 patients with varying contractile states.
Calculated PVA/MVO2 efficiency, work efficiency, and overall mechanical efficiency.
Constructed left ventricular pressure-volume loops and assessed end-systolic pressure-volume relation (Ees) slopes.

Main Results:

Pressure loading increased external work, PVA, and MVO2, decreasing work efficiency but increasing PVA/MVO2 efficiency.
Opposing changes in these efficiencies maintained constant overall mechanical efficiency.
PVA/MVO2 efficiency correlated inversely with Ees, while work efficiency correlated linearly with Ees.

Conclusions:

Left ventricular mechanical efficiency is largely unaffected by changes in loading and inotropic conditions.
This stability persists unless left ventricular contractility is significantly depressed.
The PVA concept helps explain the robustness of mechanical efficiency across different cardiac states.