Fortunately, the reserve on the supply side is large enough to make ischemia impossible in normal hearts with the most vigorous level of exercise. However, in the presence of coronary artery disease or abnormal left ventricular hypertrophy, an imbalance between supply and demand may occur with minimal exercise or even at rest. Application of the concept of supply and demand to myocardial oxygen utilization emphasizes and underlines the physiologic parameters that control oxygen delivery and consumption by the heart. buy ortho tri-cyclen online
Myocardial Oxygen Supply
The supply of oxygen to the myocardium is determined by the magnitude of coronary blood flow and the oxygen-carrying capacity of the blood. The latter is compromised in clinical circumstances such as significant anemia, hypoxemia, and carbon monoxide poisoning. However, by far, the most important determinant of oxygen supply in most clinical situations is the magnitude of coronary blood flow. Blood flow in coronary vessels is governed by the principles of fluid dynamics, namely: the flow is the result of the pressure gradient across the vascular bed divided by the resistance. Aortic root pressure minus right atrial pressure or left ventricular diastolic pressure defines the pressure gradient or perfusion pressure.