Hemodynamics Flashcards
Veins
How do you determine the systemic pressure difference that drives blood flow (Q)?
Why is turbulent flow bad in the systemic vasculature?
- Can cause endothelial damage –> inflammation, dysfunction of endothelium (important for local vasodilation and autoregulation of CV system) –> can lead to atherosclerosis and / or thrombus formation
- Local pockets of static blood that’s not moving as much –> more likely to clot
In the CV system, what determines compliance?
- Changes in […] alter peripheral venous pressure
- How can venous pressure be altered?
- Nitroglycerin is a selective venodilator. What affect will this drug have on pre-load and oxygen demand?
- Blood volume
- Changes in venous tone via SNS activation
- It will vasodilate veins, increasing blood in veins, thereby decreasing blood that is returned to heart so decrease pre-load and decrease oxygen demand
Capillaries are arranged in parallel. This allows the body to alter local vasoconstriction and vasodilation to alter blood flow locally to tissues without changing total resistance. If total resistance is unchanged and flow is constant, then pressure will not change.
What must be the relationship between the pressure gradient and vascular resistance in order for blood flow to occur?
Pressure gradient must be high enough to overcome TPR
Normally the viscosity of blood does not change. However, there are circumstances that can change viscosity. When would this happen?
Polycythemia = genetic condition, too many RBCs
What 4 factors determine the resistance to blood flow?
- decreased
Capillaries
Decrease; increase
With compliance in mind, explain why the BP measured at the brachial artery is not the same as the BP of the actual aorta.
The aorta is more compliant that the systemic arteries. Therefore, blood in the aorta will display a lower increase in pressure for a given change in volume or distention of the vessel. The systemic arteries distend less than the aorta, so for the same level of distention, there will be a larger change in pressure. Therefore, the pressure measured at the brachial artery is actually higher than it is in the aorta. The systolic pressure increases, while the diastolic pressure decreases leading to a greater pulse pressure in the BA vs. aorta.
- What does aortic pulse pressure tell you?
- How is it calculated?
- What 2 things determine PP?
- See image
- See image
- Compliance and stroke volume output
Increase, right
Venules
What is the equation for flow rate?
A * v
v = velocity
A = Cross-sectional area
Therefore, v = Q / A
- When the left ventricle ejects blood into the aorta, the aortic pressure […].
- What is systolic pressure?
- As the left ventricle is relaxing and refilling, the pressure in the aorta […].
- What is diastolic pressure?
- Rises
- The maximal aortic pressure following ejection is systolic pressure
- Falls
- The lowest pressure in the aorta, which occurs just before the ventricle ejects blood into the aorta, is diastolic pressure
- decrease, decrease
Decreased
What is central venous pressure?
BP in the thoracic vena cava near right atrium. This determines the filling pressure of the right ventricle and ventricular stroke volume and CO.
What is hemodynamics?
Let’s say a person is exercising. SNS is going to increase HR, increase contractility to increase CO. This will also increase oxygen consumption throughout the whole body, including the heart. Part of the response of the SNS is vasoconstriction. If the vessels that deliver blood to the myocardium constricted, then there would be insufficient oxygen delivered to the heart muscle to meet increased demand. How does the heart overcome the order to vasoconstrict by the SNS?
Increase in coronary blood flow (active hyperemia) triggers local vasodilatory molecules (NO and adenosine) that act counter to the order to constrict by SNS
Decreasing compliance […] pulse pressure.
Decreasing SV […] pulse pressure.
Increases
Decreases
Failure of what system to drain excess fluid leads to edema?
Lymphatic system
Arterioles
What is the single most important factor that affects resistance, and thus flow?
radius
Decrease in r –> increase in R, decrease in Q
The capillary beds cover a large area. What implications does this have for flow and velocity?
Flow will remain unchanged because the CV system is a closed system, so flow must be constant. However, V = Q/A and if Q is staying the same and A is increasing then V is decreasing when blood moves into the capillaries. This is important because this maximizes the time blood spends in the capillaries to exchange nutrients and waste.
Blood flow (Q) is determined by two factors. What are they?
Note that although Q = A * v, these factors do not determine the blood flow necesscarily. If surface area changes, a corresponding change in velocity happens to keep flow constant. However, changes in pressure and resistance can actually change the value of Q in the CV system.
- Mechanisms that cause vasoconstriction of resistance vessels SVR
- Mechanisms that cause vasodilation of resistance vessels will […] SVR
- Increase
- Decrease
What factors aid venous return to the heart?
- Structural factors inherent to the veins themselvs
- Large lumen, one way valves preventing backflow
- Skeletal muscle compression of nearby surrounding muscles
- Functional adaptations
- Innervation by SNS
