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