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.
How much oxygen does the myocardium extract from coronary arteries?
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.
How much oxygen does the myocardium extract from the coronary arteries quizlet?
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?
|Tissue type||Oxygen consumption in ml/100g/min|
|Myocardium in cardiac arrest||2|
|Myocardium contracting at rest||6-8|
|Myocardium at maximum inotropy||90|
What causes increased myocardial vo2?
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?
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?
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?
The rationale behind oxygen therapy is to increase oxygen delivery to the ischemic myocardium and thereby limit infarct size and subsequent complications. The basis for this practice is limited to experimental laboratory data and small clinical studies.
Why is oxygen bad for MI?
Oxygen therapy may decrease cardiac blood flow and perfusion reduce cardiac output and increase coronary vascular resistance. If myocardial reperfusion is achieved oxygen may have a paradoxical effect by inducing reperfusion injury through production of oxygen free radicals.
Which patient is at a high risk for myocardial infarction MI )?
Your risk is especially high if you have male family members who developed heart disease before age 55 or if you have female family members who developed heart disease before age 65. Stress. Although the evidence for this is still limited stress may also be a trigger for acute myocardial infarction.
Does nitroglycerin increase oxygenation to the myocardium?
The results show that nitroglycerin injected as a single intravenous dose or by slow infusion causes a reduction of the arterial blood pressure and of cardiac work an increase of the coronary blood flow and a reduction of oxygen consumption in the myocardium proportional to the reduced cardiac work.
What does increased oxygen supply indicate?
Prolonged exposure to higher oxygen levels at atmospheric pressure can lead to pulmonary and ocular toxicity. Symptoms of oxygen toxicity may include disorientation respiratory problems or myopia. Prolonged exposure to higher than normal partial pressures of oxygen can result in oxidative damage to cell membranes.
Does lidocaine increase oxygenation to the myocardium?
An acute bolus of lidocaine appears to transiently increase coronary blood flow by decreasing coronary vascular resistance and also decrease myocardial function. Thus an acute lidocaine bolus may favorably alter the myocardial oxygen supply/demand ratio.
How do you increase coronary blood flow?
The requirement of exercising muscle for increased blood flow necessitates an increase in cardiac output that results in increases in the three main determinants of myocardial oxygen demand: heart rate myocardial contractility and ventricular work.
When a normal heart rate is established by the SA node A?
At rest the SA nodal myocytes depolarize at an intrinsic rate between 60 and 100 beats per minute which is generally considered a normal heart rate.
How does atherosclerosis impedes coronary blood flow?
Abstract. Atherosclerosis causes clinical disease through luminal narrowing or by precipitating thrombi that obstruct blood flow to the heart (coronary heart disease) brain (ischemic stroke) or lower extremities (peripheral vascular disease).
Is the blood flow to the myocardium greatest during systole or diastole quizlet?
During systole flow is highest in the epicardial areas (less vessel compression compared to endocardial area). During Diastole flow is highest in the endocardial area because of reactive hyperemia (build up of metabolites that occurs when blood flow is cut off by the contracting ventricle during systole).
Which has a faster spontaneous depolarization rate SA node or AV node?
-The spontaneous depolarization rate of the A-V node is approximately 60 times per minute. The spontaneous depolarization rate of the Purkinje fibers is approximately 10 to 40 times per minute. Also the spontaneous rate of depolarization of the S-A node is between 60 and 100 times per minute.
During which phase of the cardiac cycle do the coronary arteries fill quizlet?
Blood flow to the coronary arteries is highest during ventricular diastole. This is the relaxation phase which allows the opportunity for blood to fill the ventricles and allows the heart to “feed” itself. In tachycardia the left ventricular coronary flow is reduced because diastole is shorter when HR is high.
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