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.
Since the Pulse Pressure is dependent on the arterial compliance, a decrease in compliance would cause it to (INCREASE/DECREASE).
Increase
***Systolic pressure would increase and diastolic may stay the same or could decrease.
For example, ___________ is a disease that decreases compliance and causes increased resistance. Pressure will also increase.
Arteriosclerosis
________ ________ is the inability to push blood through the Aortic Valve, which causes a drop in systolic pressure.
Aortic Stenosis
How are compliance and resistance related?
If you have increased compliance, there is decreased resistance. You can also think of this as the diameter of the vessel is larger because of the increased compliance, making resistance lower.
If you have decreased compliance, there is increased resistance. You can also think of this as the diameter of the vessel is smaller because of the decreased compliance, making resistance higher.
Venous pressure is (HIGH/LOW) and it has high compliance and large volume.
Low (due to the high compliance, there is less resistance)
This is the term for pressure measured by wedging a pulmonary catheter with an inflated balloon into a small pulmonary arterial branch. It estimates the left atrial pressure. Because of the large compliance of pulmonary circulation, it provides an indirect measure of the left atrial pressure and can strongly suggest when there is failure of the left ventricle output.
Pulmonary Wedge Pressure
For microcirculation, the pathway is from arterioles with smooth muscle walls to _________ with limited smooth muscle wall. From there, the blood goes to capillaries, which have _________ _________ to control the flow.
Metarterioles
Precapillary Sphincters
For the exchange of substances across the capillary wall, clefts allow passage of water soluble substances such as glucose and electrolytes. In the brain these clefts are very (LARGE/SMALL), and in the liver and gut these clefts are very (LARGE/SMALL).
Small
Large
For the exchange of substances across the capillary wall, lipid-soluble substances such as ______ and ______ pass through the cell wall. Some larger molecules may pass through in _________.
O2
CO2
Vesicles
The _________ equation calculates the flow of water either out of the capillary (+) or drawing it into the capillary (-). It is dependent on the net forces influencing the movement of water.
Starling
For the Starling equation, there are two types of force. Both of which are found on both sides of the capillary wall, intravascular (c) means moving into the vessel and extravascular or interstitial (i) means moving out of the vessel. These forces or pressures are…
Hydrostatic Pressure (P) Osmotic Pressure (π)
What is the Starling equation?
Jv = Kf [ (Pc - Pi) - (πc - πi) ]
***This means Kf [ (forces moving fluid out) - (forces moving fluid in) ]
***Net filtration would be a positive number, meaning this is what is moving out of the capillary. Net absorption would be a negative number, meaning this is what is coming into the capillary.
T/F. For the Starling equation, the net driving pressure determines the rate of fluid exit from or entry into the capillary.
True
For the Starling equation, the fluid usually leaves the capillary at the ________ end and some, but not all, returns into the capillary at the ________ end.
Arteriolar
Venous
For the Starling equation, the net exchange is a gradual leakage of fluid out of the capillary and into the interstitium which must be gathered up by the __________ system and returned to the venous circulation.
Lymphatic
What can alter the forces of the Starling equation?
Edema
Pc (into capillary) can be elevated by ________ pressure (heart failure).
Venous
Pi (out of capillary) can be restricted by ________ flow or increased driving force out of capillary.
Lymphatic
πc (into capillary) can be altered by a decrease in _________ (starvation, liver failure).
Albumin
πi (out of capillary) can be altered by restricted lymph flow or _________.
Inflammation
Excess fluid and proteins and other substances enter __________ via valved channels.
Lymphatics
Muscle pumps push lymph through lymph node ________. About 2 to 3 liters/day re-enter at the ________ vein.
“Scrubbers”
Subclavian
_______ _______ is how the Sympathetic control can global alter resistance (TPR) by stimulating the resistance beds, but local beds have an ability to break from this if the need becomes greater than is being allowed. This is called _______ _______.
Central Control
Local Control
T/F. Usually when a tissue “breaks” from Central Control, it is not sufficient to significantly alter TPR, or other tissues compensate by further constriction to maintain constant BP.
True
Describe Myogenic Control (Autoregulation).
If BP is elevated, which would otherwise deliver more blood than necessary, arterial walls become stretched. But the smooth muscle recognizes this and that is why vasoconstriction occurs, regulating the BP.
________ ________ is increasing interstitial concentration of metabolites such as CO2, H+, K+ lactate, and adenosine or the reduction of O2 due to increasing metabolic rate. This causes smooth muscle of arterioles, met arterioles, and precapillary sphincters to relax. This increases flow through the area.
Active Hyperemia
________ ________ is when vascular obstruction causes build-up of metabolites leading to vasodilation. Therefore, if the obstruction is removed the area is flooded with blood.
Reactive Hyperemia
If vascular bed dilates due to metabolic demand, the flow through upstream arterioles and small arteries would increase. This would increase the shear or wall friction, leading to the release of ______ which would cause vasodilation and augment the downstream metabolic effect.
NO
_________ stimulation causes vasoconstriction, and decreasing it would cause vasodilation.
Sympathetic
These can cause arteriolar vasodilation and increase capillary porosity (Kf) allowing the escape of large molecules. They can cause edema in response to tissue damage.
Histamine
Bradykinin
This can cause vasoconstriction in response to tissue damage.
Serotonin
This has mixed effects on vessels (vasodilation or vasoconstriction).
Prostaglandin
Coronary circulation is largely under _________ control. Sympathetic innervation of vasculature occurs, but it is usually ignored.
Metabolic
Ventricular _________, especially the Left Ventricle, causes constriction of the vasculature most notably near the __________ surface.
Contraction
Endocardial
Cerebral circulation is largely under _________ control.
Metabolic
The highest pressures of the pulmonary vascular system are found where?
Right Ventricle
Pulmonary A.
The pressure in the Right Ventricle varies from _____ mmHg (highest reading) down to between ______ mmHg (lowest reading).
24
0-4
The pressure changes are less in the Pulmonary A. with the maximum the same as the Right Ventricle (24 mmHg) but the minimum being greater at near ______ mmHg. The average pressure in the Pulmonary A. is _______ mmHg.
10-16
20
Small Pulmonary As. will vasoconstrict during ________ ________, meaning the oxygen levels are very low.
Alveolar Hypoxia
The Pulmonary circulation has little Sympathetic influence and there arterial system is much more _________ than the systemic arteries. Therefore, relatively small changes in mean pressure will significantly dilate arteries, reduce ________ and help maintain pressure low in the face of large changes in flow.
Compliant
Resistance
***Remember, the pressure in the Pulmonary circulation is much lower than the Systemic circulation because of its low resistance and high compliance.
At rest, skeletal muscle is under central baroreceptor control. Normally, its NT is __________ which binds to _______ receptors. When active, it comes under local control.
Norepinephrine
Alpha-Adrenergic
When skeletal muscle is active, motor centers cause generalized increase in Sympathetic outflow, causing increased ______ and non-muscular vascular resistance. This response compensates for an anticipated drop in ______ by the skeletal muscle metabolic dilation and helps maintain BP constant.
CO
TPR
During flight response, Adrenal Glands secrete _________ which bind to ________ receptors. These receptors cause vasodilation.
Epinephrine
Beta2-Adrenergic
For the skin, sympathetic vasoconstriction leads to baroreceptor reflex. Sympathetic inhibition and dilation of shunt pathways leads to excessive ________ ________.
Body temperature
This shunt is the blood passing from Systemic Veins to Systemic Arteries without passing through functional lung tissue.
Right to Left Shunt
This shunt is blood passing from Systemic Arteries to Systemic Veins without passing through a capillary bed for substance exchange.
Left to Right Shunt
What tissues have the best Local Control capabilities?
Heart
Brain
Muscle (When active)
***Review table on slide 22!
