Lecture 11 (DSA): Hemodynamics & Systemic Circulation Flashcards
The site of highest resistance to blood flow is within?
Arterioles
Arterioles are extensively innervated by?
Sympathetic nervous system
α1-Adrenergic receptors are found within arterioles cause what?
Constriction of vascular smooth muscle
How does constriction of arterioles affect resistance to blood flow?
Increases resistance, which decreases blood flow
β2-adrenergic receptors are found within arterioles and cause what?
Dilation/relaxation of the vascular smooth muscle
How does dilation of arterioles affect resistance to blood flow?
Deceases resistance, which increases blood flow
How do α1-Adrenergic receptors affect BP?
When stimulated will cause constriction of arterioles = increasing BP
What is the of nutrient, gas, water, and solute exchange within circulation?
Capillaries
Why are capillaries the ideal site for the exchange of substances?
They have a large internal surface area
What is the benefit of the capillaries having a large total cross-sectional area?
Blood moves very slowly through them, which maximizes the time for exchange across the capillary walls.
The largest percentage of blood in the cardiovascular system is found within?
Veins
Veins contain what kind of receptors?
α1-Adrenergic receptors
For a given flow the velocity will be _______ the larger the vessel is through which it is flowing
slower
What kind of relationships exists between velocity of flow and cross-sectional area?
Inverse relationship
V = Q/A
What is the equation for blood flow?
Q = (delta)P/R
Direction of blood flow is determined by what; and is always in what direction?
Direction of the pressure gradient; always from high to low pressure
Why does blood flow from the ventricle into the aorta and not in the other direction?
Pressure in the ventricle is higher than pressure in the aorta (high to low)
The magnitude of blood flow (Q) is directly proportional to the size of the?
Pressure difference (deltaP)
Major mechanism for changing blood flow in the CV system is by changing the resistance of blood vessels, particularly which ones?
Arterioles
How does changes to the radius of a blood vessel affect resistance?
Has a very powerful effect, in Poiseullie’s equation r^4
If the radius of a blood vessel decreases by one-half resistance will increase by?
16-fold (2^4)
If the radius of a blood vessel decreases by three-fourths the resistance will increase by?
1/(1/4)^4 = 4^4 = 256-fold
The total resistance of the system arranged in series is equal to?
The sum of individual resistances
Although total flow is constant at each level in the series, what happens to pressure?
Pressure decreases progressively as blood flows through each sequential component
Where does the greatest decrease in pressure occur for blood flow, why?
In the arterioles, because they contribute the largest portion of resistance
The total resistance in a parallel arrangement is _____ than any of the individual resistances
Less
Adding a parallel resistance does what to the total resistance?
Decreases total resistance
Adding a resistance in series does what to the total resistance?
Increases total resistance
What are the effects of parallel resistance of pressure?
No loss of pressure in the major arteries
If resistance of one of the individual vessels in a parallel arrangement increases, what happens to total resistance?
Increases
In laminar flow how does velocity near the wall of the blood vessel compare to that of the center?
Velocity of flow at vessel wall is zero and at the center of stream is maximal
What is required to drive turbulent blood flow?
More energy (pressure)
What occurs to the fluid streams during turbulent flow?
Kinetic energy is wasted due to the fluid streams mixing radially and axially
What is heard while measuring BP caused by turbulent flow?
Korotkoff sounds
Blood vessel stenosis and cardiac valve disease can cause what kind of flow; and is heard as?
Turbulent flow heard as murmurs.
What is Reynolds number used for?
To predict whether blood flow will be laminar or turbulent
What is the standard number used with Reynolds number?
If Reynold’s number is greater than 2000, likeliness of turbulent blood flow is increasing. If greater than 3000 always predict turbulent flow
The major influences on Reynold’s number in the CV system are what two things?
1) Changes in viscosity
2) Changes in velocity of blood flow
Decreases in viscosity do what to Reynold’s number?
Increase
Narrowing of a blood vessel would do what to the velocity of blood flow; affect on Reynold’s number?
Increase velocity and increase Reynold’s number.
How does anemia affect Reynold’s number?
- Decreased hematocrit = decreased viscosity = increased Reynold’s number
- Increased cardiac output = increased velocity = increased Reynold’s number
What is Thrombi; how does it affect Reynold’s number?
Blood clots in the lumen of a vessel = decrease diameter = increased velocity = increased Reynold’s number.
What causes shear?
If adjacent layers of blood travel at different velocities
Where is shear highest?
Between the motionless layer of blood at the vessel wall and the next layers
Where is shear lowest?
The center of the blood vessel where the velocity of blood is highest, and adjacent layers of blood are essentially moving at the same velocity
What is a consequence of shear?
Breaks up aggregates of RBC’s and decreases blood viscosity
*At wall shear is highest, viscosity and RBC aggregates are lowest
What is compliance or capacitance of a blood vessel?
The volume of blood the vessel can hold at a given pressure
- C = V/P
Which has higher compliance, veins or arteries?
Veins have the highest compliance
Why do veins have higher compliance?
Hold larger amounts of blood at lower pressures
What occurs if there is a decrease in compliance of the veins?
Volume of blood they can hold will decrease and there will be a shift of blood from the veins —> arteries
How does compliance change as an artery ages?
There will be a decrease in compliance. At a given arterial pressure, the arteries can hold less blood.
What occurs as arteries age?
- Walls become stiffer
- Less distensible
- Less compliant
Why do elderly individuals arterial pressures increase?
To compensate for the decreased compliance
What is the driving force for blood flow?
The pressure differences that exist between the heart and the blood vessels
Where is mean pressure highest?
The aorta and large arteries
What 2 factors cause the high mean arterial pressure in the aorta?
1) Large volume of blood pumped from the left ventricle
2) Low compliance of arterial wall
Where do you see the most significant decrease in arterial pressure?
The arterioles
*High resistance to flow
Since total blood flow is constant at all levels of the CVS, what must occur as the resistance increases?
The pressure must decrease
Q = deltaP/R
What are the 2 reasons pressure decreases in the capillaries?
1) Frictional resistance to flow
2) Filtration of fluid out of the capillaries
Diastolic pressure
Lowest arterial pressure measured during a cardiac cycle and is pressure during ventricular relaxation
Systolic pressure
Highest arterial pressure measure during cardiac cycle and is pressure in arteries after blood has been ejected from left ventricle
The difference between systolic and diastolic pressure is known as?
Pulse pressure
The magnitude of the pulse pressure reflects?
Volume of blood ejected from the left ventricle on a single beat, stroke volume.
Mean arterial pressure; calculation?
Average pressure in a complete cardiac cycle
Diastolic pressure + 1/3Pulse pressure
or
((2 x diastolic) + systolic))/3
Greatest fraction of cardiac cycle is spent in?
Diastole
Systolic and pulse pressure are higher in _______ than the aorta
Large arteries
Why is systolic and pulse pressure higher in large arteries than in the aorta?
Following ejection of blood from ventricle, the pressure wave travels at a higher velocity than the blood itself
Is diastolic pressure higher or lower in the large arteries than in the aorta?
Lower in the large arteries
What 2 factors cause the dampening and loss of pulse pressure downstream?
1) Resistance of the blood vessels, particularly the arterioles
2) Compliance of the blood vessels, particularly the veins
What is arteriosclerosis?
Plaque deposits in arterial walls decrease the diameter of the arteries, decreasing compliance
How is systolic pressure, pulse pressure, and mean pressure affected in arteriosclerosis?
All increased
How does aortic stenosis affect stroke volume, systolic pressure, pulse pressure, and mean pressure?
- Size of opening which blood can be ejected is narrowed so stroke volume decreases
- Systolic, pulse, and mean pressure will all decrease
By the time blood reaches the venules and veins, pressure is less than?
10 mmHg
How does pulmonary pressure compares to systemic vasculature?
Much lower in pulmonary vasculature
How is pulmonary pressure analogous to systemic?
Pulmonary artery (highest pressure). The pressure decreases as blood moves on to arterioles, capillaries, venules, veins, and back to the left atrium.
Why is there lower pressure on the pulmonary side?
The pulmonary vascular resistance is much lower than systemic resistance.
Why is it crucial for pulmonary vascular resistance to be low?
Allows for total flow through systemic and pulmonary vasculature to be equal, even with such low pressure on the pulmonary side.
