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External mechanical work during relaxation period does not affect myocardial oxygen consumption
1Department of Cardiovascular Dynamics, National Cardiovascular Center Research Institute, Osaka, Japan.
The American Journal of Physiology
|December 1, 1991
Summary
External mechanical work during ventricular relaxation does not impact myocardial oxygen consumption. Potential energy can be converted into external work without changing oxygen use, offering insights into cardiac energetics.
Area of Science:
- Cardiovascular Physiology
- Cardiac Energetics
- Myocardial Metabolism
Background:
- Understanding myocardial oxygen consumption (VO2) is crucial for assessing cardiac efficiency.
- The pressure-volume area (PVA) represents total mechanical energy, but the role of its components, like external work (EW) and potential energy (PE), during relaxation is less understood.
Purpose of the Study:
- To investigate the effect of external mechanical work (EW) during the relaxation period (RP) on myocardial oxygen consumption (VO2).
- To clarify the energetic significance of the potential energy (PE) portion of the pressure-volume area (PVA) in the left ventricle.
Main Methods:
- Utilized a cross-circulated dog left ventricle model.
- Manipulated the pressure-volume (P-V) trajectory during the relaxation period by altering EW within a constant PVA, while keeping end-diastolic volume (EDV) and systolic trajectory unchanged.
- Measured myocardial oxygen consumption (VO2) under varying conditions of ventricular ejection and filling during RP.
Main Results:
- Marked increases in the percentage of EW within PVA (%EW/PVA) during relaxation (from ~32% to ~93% in ejecting contractions, and 0% to ~93% in isovolumic contractions) did not significantly alter myocardial oxygen consumption (VO2).
- VO2-PVA data consistently aligned with a reference relationship established under different conditions, irrespective of EW manipulation during RP.
- Demonstrated that changes in EW during RP, at a constant PVA, did not affect VO2.
Conclusions:
- External mechanical work performed during ventricular relaxation does not influence myocardial oxygen consumption when the overall pressure-volume area remains constant.
- A portion of potential energy stored in the ventricle can be converted into external mechanical work during relaxation in an energetically equivalent manner.
- These findings contribute to a deeper understanding of cardiac energetic efficiency and the mechanical determinants of myocardial oxygen demand.