15- Circulation & Hemodynamics Part 1 & 2 Flashcards
For blood circulation from the aorta, what are the different systems and what percentage of blood do they receive?
Cerebral -- 15% Coronary -- 5% Renal -- 25% GI -- 25% Skeletal Muscle -- 25% Skin -- 5%
***These can change significantly depending on activity
In the body, what vessels have the largest cross-sectional area?
Capillaries
***Veins are second
In the body, what carries the most blood volume?
Veins
***Arteries are second, but not even close to veins
For the following, match the description with the correct vessel.
A) Arteries
B) Arterioles
C) Capillaries
D) Veins
1) Large cross-sectional area, single endothelial lining, nutrient, waste and gas exchange.
2) High pressure.
3) Low pressure, large volume, can contract to move blood to arterial side to increase BP.
4) Moderate pressure, smooth muscle walls can contract to control flow by changing resistance.
1 – C
2 – A
3 – D
4 – B
What is the equation for the velocity of blood flow?
Velocity (V) = Flow (Q) / Area (A)
***Remember, Q is interchangeable with CO!
T/F. The velocity of blood flow can be calculated for a single vessel if you know its cross-sectional area and flow. It can also be determined knowing the TOTAL, summed cross-sectional area of parallel circuits and flow.
True
Because the capillaries have such a high cross-sectional area compared to the aorta, would you expect the velocity of blood flow to be very fast or slow, and why is this beneficial?
Very slow, and this is beneficial for the capillaries because they are responsible for nutrient, waste, and gas exchange. They need more time to be able to do these things.
What is the equation for the relationship between blood flow, pressure, and resistance?
Q (flow) = Delta P (Pressure Gradient) / R (Resistance)
OR
CO = (Arterial Pressure - Venous Pressure) / TPR
- **Pressure can be between any 2 points
- **Can be determined through individual vessel or segment of vessels or through an entire system!
Poiseuille’s Law calculates resistance through a section of vasculature. What is this equation for resistance and describe the relationships of the variables.
R = (8nl) / (πrˆ4)
n = viscosity — As this increases, resistance increases
l = length of vessel — As this increases, resistance increases
r = vessel radius — As this increases, resistance will decrease and vice versa.
If vascular resistances are added in series, then how can total resistance be calculated?
Add individual resistances for total
***R total = R1 + R2 + R3… etc.
If vascular resistances are added in parallel, then how can total resistance be calculated?
Add individual resistances as their reciprocal
*** 1 / R total = 1/R1 + 1/R2 + 1/R3… etc.
Adding resistance beds in series (INCREASES/DECREASES) resistance, and adding resistance beds in parallel (INCREASES/DECREASES) resistance.
Increases
Decreases
***Aka the longer the tube, the more the resistance. Series means a straight line.
This is the term for when blood is flowing in a nice even pattern.
Laminar Flow
This is an equation that takes into account density, diameter, velocity, and viscosity to predict when turbulence will occur. The higher it is, the more turbulent flow is occurring. If it’s low, the flow is laminar.
Reynold’s Number
N(R) = pdv / n
Describe Reynold’s Number and its equation, and what the variables mean.
N(R) = pdv / n
p = density — As this increases, N(R) increases and the flow is more turbulent
d = diameter — As this increases, N(R) increases and the flow is more turbulent
v = velocity — As this increases, N(R) increases and the flow is more turbulent
n = viscosity — As this increases, N(R) decreases and the flow is more laminar. If it decreases, N(R) increases and the flow is more turbulent
If N(R) is greater than _________, then it is considered to transition from laminar to turbulent flow.
2000
What can turbulent flow lead to?
Sound (bruits)
Lesions (Arteriosclerosis)
Describe the difference between laminar and turbulent flow.
Laminar flow within a vessel is very slow at the walls and fastest in the center. Think of syrup being poured out. It sticks to the bottle walls but pours out quickly in the center. And it is a thick, highly viscous substance!
Turbulent flow is erratic flow within a vessel. Think of juice being poured out. It is much harder to control and can splash or get everywhere because it is a very thin, less viscous substance!
This is the term for how easy it is to cause a vessel to expand. It determines how much a vessel will expand in response to a given change in lumen hydrostatic pressure.
Compliance
***Think of compliance as how easy it is to blow up a balloon. Large party balloons have high compliance because they’re easy to blow up and don’t require much effort. Small balloons used for balloon animals have low compliance because they are much more difficult to blow up and require more effort!
What is the equation for Compliance?
Compliance = (Change in Volume) / (Change in Pressure)
For veins, arteries, and aging arteries, describe their compliance.
Veins = Highest Compliance (They have the largest volume)
Artery = Low Compliance
Aging Arteries = Lowest Compliance (Often due to Arterial Sclerosis, making them stiffer and harder to blow up)
Explain what smooth muscle contraction does to venous compliance and the effects it causes.
In veins, the smooth muscle constricts the vessel, which causes decreased compliance and forces more blood volume from the veins to the arteries. This ultimately increases blood pressure.
***Another way to think about it is that the smooth muscle constricts the vessel, thus decreasing the vein diameter. The compliance doesn’t necessarily change. This decrease in diameter in the veins causes more blood volume to shift to the arteries, resulting in increased blood pressure.
Put the following vessels in order from HIGHEST pressure to LOWEST:
A. Arterioles B. Veins C. Small arteries D. Aorta E. Venues F. Capillaries G. Large arteries
1 -- G 2 -- D 3 -- C 4 -- A 5 -- F 6 -- E 7 -- B
The aorta, large arteries, and small arteries have what is called a “Pulse Pressure” because it moves between periods of contraction and relaxation (compliance and distension). Aka, systole and diastole. Why do the large arteries have an increased pulse pressure than the aorta?
The larger arteries have an echo effect that bounce off the arterial walls, making a larger pulse pressure.
Where does the largest pressure drop occur in the systemic circulation?
In the arterioles
***This is the point where pulse pressure is lost!
The clinically reported (DIASTOLIC/SYSTOLIC) pressure is the greatest pressure reached in the large arteries, and the (DIASTOLIC/SYSTOLIC) pressure is the lowest pressure reach in the larger arteries.
Systolic (120)
Diastolic (80)
How can the pulse pressure be measured?
Pulse Pressure = Systolic - Diastolic
***In this case, 120 - 80 = 40
What is the normal MAP?
93.3
***Remember, it is MAP = Diastolic + 1/3 Pulse
Why is the MAP closer to Diastolic than Systolic?
Because more time is spent in Diastole than Systole.
Why is the pressure lower in the Pulmonary circulation compared to the Systemic circulation?
Because resistance is much less! The vasculature has much shorter lengths.