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Related Experiment Videos

Oxygen delivery does not limit cardiac performance during high work states.

J Zhang1, Y Murakami, Y Zhang

  • 1Departments of Medicine, Biochemistry, Radiology, and the Center for Magnetic Resonance Research, University of Minnesota Health Sciences Center, Minneapolis, MN 55455, USA. zhang047@tc.umn.edu

The American Journal of Physiology
|July 17, 1999
PubMed
Summary

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High cardiac work states do not deplete myocardial high-energy phosphates (HEP) due to insufficient oxygen. Myocardial oxygenation levels are crucial for interpreting HEP changes during increased cardiac workload.

Area of Science:

  • Cardiovascular Physiology
  • Biophysics
  • Biochemistry

Background:

  • High cardiac work states can lead to a decrease in myocardial high-energy phosphates (HEP).
  • It is hypothesized that this depletion is not caused by insufficient intracellular oxygen availability.

Purpose of the Study:

  • To test the hypothesis that myocardial HEP loss during high cardiac work is not due to inadequate oxygen supply.
  • To evaluate myocardial oxygenation using deoxymyoglobin (Mb-delta) and HEP using phosphorus-31 magnetic resonance spectroscopy (MRS).

Main Methods:

  • Studied normal dogs (n=11) under basal and high-work states (dobutamine and dopamine infusion).
  • Measured deoxymyoglobin (Mb-delta) via proton (1H) MRS and high-energy phosphates (HEP) via phosphorus-31 (31P) MRS.
  • Normalized Mb-delta to the signal during total coronary occlusion; expressed creatine phosphate (CP) as CP/ATP.

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Main Results:

  • During high cardiac work, CP/ATP decreased significantly (2.22 to 1.83), and DeltaP(i)/CP increased (0 to 0.21), indicating HEP changes.
  • Despite significant HEP changes, Mb-delta remained undetectable during high work states without coronary occlusion.
  • Coronary stenosis causing similar HEP reduction readily detected Mb-delta (0.38 of total occlusion value).

Conclusions:

  • Myocardial HEP changes during high cardiac work are not caused by insufficient oxygen availability to mitochondria.
  • Detectable deoxymyoglobin indicates limited oxygen supply, but its absence during high workload suggests other mechanisms for HEP reduction.
  • Interpreting alterations in high-energy phosphates requires simultaneous assessment of myocyte oxygenation levels.