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Am J Physiol Heart Circ Physiol 280: H318-H326, 2001;
0363-6135/01 $5.00
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Vol. 280, Issue 1, H318-H326, January 2001

Myocardial oxygenation and high-energy phosphate levels during graded coronary hypoperfusion

Jianyi Zhang, Kamil Ugurbil, Arthur H. L. From, and Robert J. Bache

Departments of Medicine and Radiology and Center for Magnetic Resonance Research, University of Minnesota Health Sciences Center and Minneapolis Veterans Affairs Medical Center, Minneapolis, Minnesota 55455

This study was performed to determine the myocyte PO2 required to sustain normal high-energy phosphate (HEP) levels in the in vivo heart. In 10 normal dogs, myocyte PO2 values were calculated from the myocardial deoxymyoglobin resonance (Mb-delta ) intensity determined with 1H-NMR spectroscopy during sequential flow reductions produced by a hydraulic occluder that decreased coronary perfusion pressure to ~60, 50, and 40 mmHg and, finally, during total occlusion. Myocardial blood flow was measured with microspheres, and HEP levels were determined with 31P magnetic resonance spectroscopy. During control conditions, Mb-delta was undetectable. Myocardial blood flow was 1.11 ± 0.06 ml · min-1 · g-1 during basal conditions and decreased with sequential graded occlusions to 0.78 ± 0.05, 0.58 ± 0.03, and 0.38 ± 0.04 ml · min-1 · g-1, respectively; blood flow during total occlusion was 0.07 ± 0.02 ml · min-1 · g-1. Reductions of blood flow caused progressive increases of Mb-delta , which were associated with decreases of phosphocreatine (PCr), ATP, and the PCr-to-ATP ratio, as well as progressive increases of the Pi-to-PCr ratio. There was a strong linear correlation between normalized blood flow and Mb-delta (R2 = 0.89, P < 0.01). Reductions of HEP and PO2 were also highly correlated (although nonlinearly); with the assumption that myoglobin was 90% saturated with O2 during basal conditions and 5% saturated during total coronary occlusion, the intracellular PO2 values for 20% reductions of PCr and ATP were ~4.4 and ~0.9 mmHg, respectively. The data indicate that O2 availability plays an increasing role in regulation of oxidative phosphorylation when mean intracellular PO2 values fall below 5 mmHg in the in vivo heart.

myocardium; blood flow; myoglobin oxygen saturation; ischemia


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