Cardiovascular Physiology Concepts
                                    Richard E. Klabunde, Ph.D.

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Arrhythmias

Cardiac Valve Disease

Coronary Artery Disease

Edema

Heart Failure

Hypertension

Peripheral Artery Disease

Click here for information on Cardiovascular Physiology Concepts, published by Lippincott Williams & Wilkins (2005)

 

Oxygen Supply

 

Oxygen is supplied to the myocardium by the coronary circulation.   Coronary blood flow  is determined by hemodynamic factors such as perfusion pressure and vascular resistance. The latter is determined by vascular anatomy and structure, as well as by changes in diameter of the vascular lumen resulting from contraction and relaxation of vascular smooth muscle (local regulation of blood flow).

The delivery of oxygen to the myocardium (oxygen supply) is determined by two factors: coronary blood flow (CBF) and the oxygen content of the blood (AO2).

O2 Delivery = CBF x AO2,

where CBF = ml/min and AO2 = ml O2/ml blood

Therefore, the units for O2 delivery are ml O2/min. The normal content of oxygen in arterial blood is about 20 ml O2/100 ml blood (0.2 ml O2/ml blood), or 20 vol %. CBF, expressed per 100g of tissue weight is about 80 ml/min per 100g at resting heart rates. Therefore, the oxygen delivery to the heart under resting conditions is about 16 ml O2/min per 100g.

Ordinarily, the oxygen content of arterial blood changes relatively little. Therefore, the primary determinant of oxygen delivery in the absence of hypoxemia is coronary blood flow.

In coronary artery disease, a number of factors can reduce coronary blood flow. Stenotic lesions cause a narrowing of vessel, particularly the large epicardial coronaries (e.g., left anterior descending or circumflex arteries). The stenosis may be at a specific site, or it may diffuse along the length of the vessel. In either case, the stenosis can limit maximal coronary flow (decreased coronary flow reserve.  Maximal flow is reduced because the the fixed stenosis is in-series with the distal microcirculation. Diseased coronary vessels are more susceptible to vasospasm, which can lead to a temporary restriction of coronary flow at rest. This can occur during stressful conditions or during exercise in susceptible individuals. Finally, thrombus formation, particularly at the site of a ruptured atherosclerotic plaque, can partially or completely occlude a coronary vessel causing unstable angina or myocardial infarction.

RK Revised 04/05/2007

DISCLAIMER: These materials are for educational purposes only, and are not a source of medical decision-making advice.

© 1999-2007 Richard E. Klabunde, all rights reserved.