Flashcards in Special Circulations: Coronary and Skeletal Deck (40)
What is the dominant coronary artery?
It varies from individual to individual, but the right coronary is dominant in 50% of people.
What are the determinants of coronary blood flow?
What is the primary determinant of the coronary blood flow?
What is the primary regulator of the the coronary blood flow?
How does tissue pressure (mechanical) determine the coronary blood flow?
Tissue pressure from the LV influences the left coronary blood flow more than the right coronary and the highest tissue pressure occurs during early systole. This can cause the reversal of left coronary blood flow in early systole and it is not until early diastole when tissue pressure falls when the the maximal blood flow to the left coronary occurs.
How much of the LV perfusion occurs during diastole?
Where is the LV EDP the greatest?
LV EDP is greatest near the endocardium.
How does LV end diastolic pressure affect the endocardial and epicardial blood flow in normal conditions?
LV EDP is greatest near the endocardium and is the least near the epicardium so endocardial vessels are more compressed but blood flow remains equal due to the greater dilation of the endocardial vessels.
How does LV end diastolic pressure affect the endocardial and epicardial blood flow in abnormal conditions?
In abnormal conditions, such as aortic stenosis, regurgitation or congestive heart failure, the greater endocardial pressure will restrict coronary blood flow and cause subendocardial ischemia.
What happens to the endocardial tissue as the diastolic coronary blood pressure falls?
The endocardial blood flow will be restricted more that the epicardial blood flow because of the greater endocardial tissue pressure.
Which tissue of the heart is most at risk for ischemia?
Describe the neural regulation of coronary blood flow including the α, β1 and β2 receptors.
Neural regulation of coronary blood flow is weak.
α - activate weak vasoconstriction
β1 - cause strong vasodilation in response to increased metabolism
β2 - vasodilation but are less sensitive to NE stimulation
What is the relationship between metabolism and coronary blood flow?
It is a linear relationship.
What occurs with increased myocardial metabolism?
Decreased coronary resistance
Increased coronary blood flow
What are the main metabolic substrates of the heart?
What is the O2 supply of the heart limited by?
It is limited by flow. The heart cannot extract more O2 from blood like muscle can and so it can only increase blood flow.
What is the O2 consumption of the heart related to?
It is directly related to the work of the heart.
What kind of work consumes the most O2?
Pressure work consumes more O2 than volume work. Increasing the arterial pressure will increase the O2 consumption much more than increasing the stroke volume of the heart.
What are some factors that determine the myocardial oxygen supply?
Diastolic Perfusion Pressure
Coronary Vascular Resistance
O2 Carrying Capacity of Blood
What are some factors that contribute to the O2 demand of the heart?
What is never a primary cause of ischemia?
Excessive O2 demand
What is the cause of ischemia?
It is caused by a relative lack of blood flow due to an imbalance in the ratio of O2 supply to demand.
Can the collateral circulations of the heart prevent MI?
No, the vessels are insufficient to prevent sudden infarction, but in response to gradual obstruction, the collateral vessels can grow and restore adequate amounts of blood supply to the myocardium.
What is coronary steal?
Coronary steal is where an increase in blood flow in one region of the heart can cause a decrease in blood flow in another region.
Describe compensated coronary steal.
Compensated coronary steal occurs when one vessel is partially blocked by atherosclerosis and leads to ischemia in this region. Compensation occurs when the vessel is maximally dilated to increase the blood flow. The vessels in the same branch that are unaffected will be vasocontricted as normal.
Describe uncompensated coronary steal.
Uncompensated coronary steal occurs when the cardiac work is increased like in exercise and the ischemic vessel that is normally compensated for cannot dilate any further, while the non-ischemic vessels can dilate. This will draw blood away from the ischemic region and make it more ischemic as a result.
What is peripheral artery disease?
It is where that is a limping due to pain in the calf or thigh with walking because of the metabolites that have built up due to uncompensated blood steal.
What is the largest vascular bed in the body?
How much of the cardiac output goes to skeletal muscle at rest?