This myocardial oxygen consumption (MVO2) calculator determines the quantity of oxygen used by cardiac function based on coronary flow and arteriovenous oxygen difference. The formula used is explained in the text below, along with the main factors that affect MVO2.
How does the myocardial oxygen consumption (MVO2) calculator work?
This health tool calculates the heart oxygen consumption based on coronary blood flow and arteriovenous difference in the oxygen content. The MVO2 is expressed in mL O2/100 g myocardium/min.
The two variables used are:
■ Coronary blood flow – measured in mL blood/100 g myocardium/min. Represents the circulation of blood in the coronary arteries and cardiac veins. Regulatory mechanisms of vasodilation or vasoconstriction act according to the oxygen requirements of the heart. Decreases in blood flow when oxygen requirement is high can result in tissue ischemia, the severe cases leading to myocardial infarction.
■ Arteriovenous difference in O2 content – measured in mL O2/100 mL. It is also known as a-vO2 diff and provides information on the quantity of oxygen that is circulated through the capillaries (the difference between oxygenated and deoxygenated blood). Along the cardiac output, a-vO2 diff is used in the regulatory mechanisms of the cardiovascular system.
The myocardial oxygen consumption MVO2 calculator uses the following formula:
MVO2 = Coronary blood flow in blood/100 g myocardium/min x Arteriovenous difference in O2 content in mL O2/100 mL.
The average value for MVO2 = 25 to 35 mL/min for an average myocardial weight of 300 g.
MVO2 accounts for 10% of total basal oxygen consumption.
Factors affecting MVO2
The main determinants of the myocardial oxygen consumption are:
■ Myocardial wall tension (intraparietal tension) – depends on the intraventricular pressure and volume.
■ Heart rate – measured in beats per minute.
■ Contractility – also known as myocardial inotropism. When the velocity of left ventricular contraction increases by 50%, MVO2 increases by 40%.
There are other factors that contribute to increases and decreases in MVO2, such as:
■ Basal energy metabolism – accounts for about 20% of the MVO2.
■ External cardiac work – refers to the work performed during the ejection phase which accounts about 15% of the MVO2.
■ Electrical activation energy – represents about 0.5% of the MVO2.
■ Ventricular relaxation – which accounts for 15% of the MVO2, it is subject to decrease via calcium concentration.
References
1) Delaye J, Mpetshi I, Durand JP. (1983) Oxygen requirements of the myocardium. Arch Mal Coeur Vaiss; 76 Spec No:7-12.
2) Gibbs CL. (1995) Mechanical determinants of myocardial oxygen consumption. Clin Exp Pharmacol Physiol; 22(1):1-9.
3) Baller D, Wolpers HG, Hoeft A, Korb H, Rösick A, Hellige G, Bretschneider HJ. (1984) Increase of myocardial oxygen consumption due to active diastolic wall tension. Basic Res Cardiol; 79(2):176-85.
4) Devereux RB, Wachtell K, Gerdts E, Aurup P, Boman K, Edelman J, Nieminen M, Papademetriou V, Wan Y, Dahlof B, Julius S. (2003) Association of left ventricular hypertrophy regression and heart rate reduction with determinants of myocardial oxygen consumption and cardiovascular events: The LIFE study. Journal of the American College of Cardiology; Vol.41(6), pp.400-400.
5) Braunwald E. (1999) Myocardial oxygen consumption: the quest for its determinants and some clinical fallout. Journal of the American College of Cardiology; Vol.34(5), pp.1365-1368.
06 Dec, 2016