Page 13, O2 Uptake, Exercise & Cor. Circ., Dr. D. Penney
The heart is a predominantly aerobic organ with a continuous and substantial need for oxygen. It is only 0.5% of body weight but accounts for about 12% of heat production, indicating a very high rate of metabolism. For this reason, oxygen utilization is high, 6 - 8 ml/100 g/min. This is 20-40 fold higher than resting skeletal muscle (0.15 ml/100 g/min). In the absence of beating, oxygen utilization is 1.5 ml/100 g/min, thus 80% of myocardial oxygen consumption is related to contraction. In the normal heart oxygen utilization may be increased 3-6 fold. O2 uptake is better correlated with tension development than with external cardiac work.
The myocardium uses fatty acids, lactate, glucose, ketoacids and amino acids as fuels, although fatty acid normally makes up 2/3's of the fuel source. During times when the oxygen demand exceeds supply, glycogen is broken down, releasing lactate, instead of lactate being consumed. This occurs most readily in the subendocardium. Because the heart can incur only a small oxygen debt, cell damage results from prolonged periods of ischemia and/or anoxia. Its anaerobic capacity is small and can support only a fraction of the energy needs.
BACK TO INDEX