When The Myocardium Requires More Oxygen

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What happens when the myocardium requires more oxygen?

Acute Coronary Syndrome. When myocardial oxygen demand is higher than supply the myocardium must use anaerobic metabolism to meet energy demands. This system can be maintained for only a short period of time before tissue ischemia will occur which typically results in angina (chest pain).

What happens when the myocardium is deprived of oxygen?

Overview. A heart attack (myocardial infarction) happens when one or more areas of the heart muscle don’t get enough oxygen. This happens when blood flow to the heart muscle is blocked.

How do you increase oxygenation to the myocardium?

Since the oxygen content of coronary sinus blood is very low only limited increases in oxygen extraction are possible. Therefore coronary dilation is the primary mechanism for increasing myocardial oxygen delivery.

What is myocardial oxygen demand?

Myocardial oxygen demand is the amount of oxygen that the heart requires to maintain optimal function and myocardial oxygen supply is the amount of oxygen provided to the heart by the blood which is controlled by the coronary arteries.

How does the myocardium get oxygen?

Oxygen is supplied to the heart muscle (myocardium) by the coronary circulation. Coronary blood flow is determined by hemodynamic factors such as perfusion pressure and vascular resistance.

Which medication causes the greatest increase in myocardial oxygen consumption?

Dobutamine was found to be associated with a greater increase in myocardial oxygen consumption when com- pared to epinephrine and isoproterenol in high doses and under these circumstances epinephrine produced a greater oxygen consumption effect than isoproterenol.

At rest approximately 60% to 70% of oxygen is extracted from blood in the coronary arteries.

What factors increase oxygen requirements in a patient experiencing a myocardial infarction?

Heart rate contractility and ventricular-wall tension are the three factors that determine myocardial oxygen demand. An increase in any of these variables requires the body to adapt to sustain adequate oxygen supply to the heart.

In which disease there is imbalance oxygen supply and the oxygen demand of the myocardium?

Under certain pathologic states such as coronary artery disease the supply of oxygen may be exhausted and an imbalance between supply and demand occurs which is translated into ischemia. The area of myocardium most susceptible to ischemia is the subendocardium due to mechanical and metabolic forces.

How does myocardium regulate blood flow?

Regulation of coronary blood flow is understood to be dictated through multiple mechanisms including extravascular compressive forces (tissue pressure) coronary perfusion pressure myogenic local metabolic endothelial as well as neural and hormonal influences.

Therefore the oxygen extraction level of coronary blood is 70% (100% -30% assuming 100% saturation for coronary arterial blood).

Does angina affect oxygen levels?

Angina occurs when blood flow to the heart is impaired causing the heart muscle to be deprived of oxygen. This deprivation of oxygen-rich blood leads to symptoms of angina. Impaired blood flow to the heart is often caused by coronary artery disease where your arteries become narrower.

How much oxygen does the heart need?

Myocardial oxygen consumption and demand

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What causes increased myocardial vo2?

Myocyte contraction is the primary factor determining myocardial oxygen consumption (MVO2) above basal levels. Therefore factors that enhance tension development by the cardiac muscle cells the rate of tension development or the number of tension generating cycles per unit time will increase MVO2.

What decreases myocardial oxygen demand?

Myocardial oxygen demand can be decreased by decreasing 1) heart rate 2) contractility (inotropy) 3) ventricular afterload and 4) ventricular preload.

How does the heart receives oxygen and nutrients?

As the ventricle contracts blood leaves the heart through the pulmonic valve into the pulmonary artery and to the lungs where it is oxygenated and then returns to the left atrium through the pulmonary veins.

Which drugs reduce the hearts demand for oxygen by lowering heart rate?

Beta blockers.

These medications slow your heart rate and reduce the heart’s demand for oxygen. Your doctor may prescribe a beta blocker if you have high blood pressure or angina or have had a heart attack.

Does vasopressin decrease myocardial oxygen demand?

Vasopressin produced myocardial dysfunction indicated by decrements in contractile and relaxation indices without evidence of global ischemia. Epinephrine restored the mechanical performance to normal without significant change in coronary blood flow myocardial oxygen consumption or lactate and potassium balance.

Does aspirin increase myocardial oxygen delivery?

In addition aspirin is not likely to affect myocardial oxygen mismatches resulting from exertion or arterial spasm but if these other causes of ischemia are treated it may be possible to unmask the effect of aspirin.

Which organ has the highest oxygen concentration?

The highest oxygen concentration within the body is in the pulmonary veins.

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Does more blood flow through the coronary arteries during ventricular diastole?

Blood flow into the coronary arteries is greatest during ventricular diastole when aortic pressure is highest and it is greater than in the coronaries.

What percentage of cardiac output does the myocardium receive when the body is at rest?

The resting coronary blood flow is ∼250 ml min−1 (0.8 ml min−1 g−1 of heart muscle) this represents 5% of cardiac output.

Why is oxygen used in myocardial infarction?

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