Final answer:
Myocardial oxygen consumption depends on heart rate, stroke volume, and contraction strength. It increases with sympathetic nervous stimulation, elevated catecholamines, thyroid hormones, and increased calcium ion levels. These changes support the heart's increased activity and oxygen demand.
Step-by-step explanation:
The myocardial oxygen consumption (MVO²) is primarily dependent on heart rate, stroke volume, and myocardial contractility. Factors that can lead to an increase in MVO² typically include an increase in heart rate, a rise in blood pressure, and enhanced ventricular contractility.The heart requires a constant supply of oxygen to function effectively, especially to maintain the metabolic processes required for contracting muscles. Under normal conditions, the heart muscle, or myocardium, uses oxygen that is delivered bound to hemoglobin in erythrocytes and stored in myoglobin within the muscle cells themselves. This dual oxygen supply is typically adequate even when the demand is heightened.
However, during periods of increased activity, such as exercise, the oxygen demand of the heart increases. Cardiac output—the volume of blood the heart pumps per minute—also rises to push more blood and thus oxygen to active tissues. The sympathetic nervous system responds to heightened physical activity by stimulating the heart to beat faster and with more force, which subsequently elevates myocardial oxygen consumption. Hormones like epinephrine and norepinephrine released during stressful or physically exertive situations also increase the heart's workload and hence its oxygen need.