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Cardiopulmonary Renal > Hemodynamics 2 > Flashcards

Hemodynamics 2 Flashcards

1
Q

What are the types of blood flow?

A
  • laminar flow

- tubular flow

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2
Q

What is laminar flow?.

A

Parabolic. Profile:
Concentric rings of equal flow rates;
Slowest at the edges(friction with the walls) highest at the center

Flow is silent

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3
Q

What is turbulent flow?

A

Occurs when laminar flow is disrupted

Requires an increased pressure to maintain flow (flow is not as efficient)

NOISY- heard by auscultation. Called bruit. Eddies are chaotic

Reynolds number is used to predict whether blood flow is laminar or turbulent

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4
Q

What is the significance of laminar flow?

A

In laminar flow adjacent layers of blood slide past each other. The layers in the center of the tube have a greater velocity than those nearer the walls; giving a parabolic shape of the flow. Shear is the sliding motion of one lamina past another. Shear causes the red cells to orientate preferentially in the direction of flow and move a little towards the central axis. This leaves a thin, cell - deficient layer of plasma next to vessel wall. This marginal plasma layer is very important since it facilitates blood flow since turbulent flow requires since turbulent flow requires much more energy to move the blood. Laminar flow is silent

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5
Q

When does laminar flow become tubular flow?

A

Turbulence increase resistance when the Reynolds number exceeds 2000

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6
Q

What factors increase turbulence?

A

High flow velocity (v)

Large vessel diameter (D)

High blood density (p)

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7
Q

What factors decrease turbulence?

A

Increased viscosity (n)

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8
Q

What is Reynolds equation?

A

Reynolds number (Re)= pro-turbulent factors: anti-turbulence factors

Re= vDp/n

Critical value for Re= 2000

When Re > 2000 laminar flow becomes turbulent

Velocity most important as: viscosity, density usually constant

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9
Q

Why does vessel diameter D increase turbulence ?

A

Blood flow is slower at the surface of the vessels: the larger the vessel the smaller the surface area: volume ratio. Contact with the vessel wall (surface area contact) slows velocity (v) because of resistance

Decreased SA / volume ratio occurs with increased diameter
-reduced blood in contact with a surface area

  • increased turbulence
  • think a bigger tube- more area in the middle for turbulence to occur

Re= vDp/n

Although- increased velocity of blood favors turbulence

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10
Q

What are the clinical conditions promoting turbulence?

A

Heart: defective valves
Blood vessels: narrowed blood vessels

Large diameter vessels favor turbulence expected in small diameter vessels.
High velocity flow flavors turbulence

Bit high velocity glow is found in narrow diameter vessels

Apparent contradiction. Question is which has the most effect on promoting turbulence ? The increased velocity of flow in narrowed vessels outweigh the benefit that narrowed vessels give.

So, narrowed blood vessels, have a high velocity of flow, and blood flow tends to be turbulent,..

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11
Q

Describe single line flow as a type of blood flow

A
  • occurs in capillaries
  • RBC diameter > capillary diameter
  • RBC flexes as passes through the capillary
  • RBC actually flows faster than plasma (less friction in axial flow, vs plasma at boundary flow)
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12
Q

How does sickle cell blood flow affect single line blood flow?

A

Red blood cell (RBC) is rigid, hemoglobin Hb rod-like and RBC sickle shape. Do not pass easily through capillary —> tissue ischemia and painful “sick line crisis”

Low blood flow: RBCs may stick together and to endothelial lining

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13
Q

What is the math behind Laplace’s law?

A

Transmural pressure (🔼P)= Pi - Pt

T= tension in vessel wall to counteract pressure

Wall thicknesse excluded- You will learn about this later

Laplace’s law= 🔼P= 2T/r

If the pressure inside this wall is constant , the larger the radius (diameter) of the vessel, the greater the wall tension needed

For same pressure: larger vessel, requires greater wall tension

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14
Q

What is the medical example of Laplace’s law?

A

Aneurysm; wall stress= pressure* tension/radius

  • frequent in large arteries (aorta) due to Laplace law
  • Aorts distension
    • aorta radius large- requires more tension to offset given blood pressure

Reaches a point where vessel cannot generate more wall tension

Eventually aneurysm can rupture

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15
Q

Describe the compliance and elastic properties of arteries and veins

A

Large arteries and veins contribute very little to overall resistance to blood flow. Therefore changes in their diameter have minimal effect on blood flow. However, the compliance and elastic properties of arteries and veins are important because it determines how much blood can be stored with them. Veins, especially, act as reservoirs of blood

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16
Q

What is compliance ?

A

Compliance describes how the volume of a compartment changes (🔼V )in response to a given change in the pressure within (🔼P)

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17
Q

Compare compliance of veins and arteries

A

Veins are more compliant. For a small change in pressure they can increase their volume greatly. Compliance =🔼V/🔼P

Compliance is a measure of “distensibility”

Veins are more distensible than arteries

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18
Q

Why are veins highly compliant at operating pressures?

A

at their operating pressures (0-10 mmHg), veins are highly compliant

Veinous pooling
So if the distending pressure is high then the veins will distend and accommodate the blood.

On standing, the pressure (distending) in the veins of the foot increases, and since the veins are so compliant these veins will accommodate a large volume of blood. This results in “veinous pooling”

Note that venous pooling will result in a fall in VR to the heart

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19
Q

What are the effects of venom obstruction?

A

Venockbstrictionn squeezes blood out of the veins and shifts it towards the heart

I.e. increased VR note: venoconstriction is akin to decreased compliance (sympathetic activity decreased venous compliance)

20
Q

What are the effects of venodilation?

A

Conversely, venodilation allows more blood to pool in the veins and decreased VR

Note: venodilation is akin to increased compliance (sympathetic activity increased venous compliance)

21
Q

Describe vena cava compliance

A

At high pressures-all fibers stretched, once the vein has circular profile, it does not increase its diameter because it has little elastin in its walls

Very compliant

Vascular tone (SNS) shifts compliance curve down and to the right

Steep slope at low pressures:

  • low pressure/volume, large veins collapse
  • increased pressure/volume, increased circular shape
  • until vessel vessels attain circular shape, walls not stretched much
  • small changes in pressure with large changes in volume
22
Q

Summarize compliance as well as contrast in veins and arteries

A

Compliance is the change in volume with distending pressure

Veins are more compliant than arteries

Flip the axis:

Slope= 1/ compliance= elastance

Arteries are more elastic than veins

23
Q

What is elasticity?

A

Ability of a vessel to recoil to a distending pressure

24
Q

Describe aortic compliance and elastic properties

A

Not as compliant as veins greater elasticity

In early phase of cardiac ejection, the aortic volume increases because there is more blood entering the aorta than leaving it. So the elastic aorta is stretched.

Towards the end of systole and during diastole, the stretched aortic and arterial walls recoil and in the process give up their stored potential energy. This reconverted energy. This reconverted energy drives blood around the circulation

25
Q

What are the main functions of aorta and arteries?

A

Aorta (and arteries) develop and withstand high pressures. Stable resistance. Therefore changes in their diameter have minimal effect on blood flow. They convert the pulsatile flow from heart into steady flow through the vascular beds

Decreased compliance in artery (stiffness) comes with an increase in pressure. Thus pressures higher in arteries

26
Q

Describe arterial compliance & age

A

Aortic compliance is clinically important in the elderly

Old artery less compliant/stiffer than young artery

At a given MAP, old arteries hold less blood than young

For an old artery to hold the same volume of blood as a young artery, the pressure in the old artery must be higher.

Systolic BP and pulse pressure in elderly> young

Systolic hypertension of the elderly (diastolic can be normal)

27
Q

How does the reduced compliance of the old aorta affect the blood pressure?

A

Normally, when about 70 ml of blood (I.e. typical SV value) is ejected into the aorta, the aortic pressure rises from about 80 mmHg to about 120 mmHg which is the systolic BP

Ejection of 70 ml of blood into an aorta which is less compliant means that the systolic BP rises to much greater values e.g. up to 160 mmHg

Diastolic BP MSY be normal (at about 80 mmHg)

Therefore, elderly person BP = 160/80 mmHg
Condition is called “systolic hypertension of the elderly”

28
Q

What are the effects of altered compliance?

A

Decreased ventricular compliance leads to increased LVEDPr and vice versa

LV hypertrophy leads to decreased compliance and increased LVEDPr

Dilated cardiomyopathies lead to increased compliance and decreased LVEDPr

29
Q

What are the consequences of reduced ventricular compliance?

A

LV hypertrophy—> increased wall thickness —> decreased compliance —> increased LV End diastolic Pr —> decreased filling —> decreased stroke volume —> decreased cardiac output

30
Q

Describe the measurement of blood pressure

A

Sphygmomanometry

Inflate cuff to > 180 mmHg

Auscultate brachial artery

Reduce cuff pressure slowly

1st korotkoff sound is when cuff pressure is just below systolic BP - due to transient spurt of blood into artery = systolic BP

Korotkoff sounds grow louder

As cuff pressure approaches diastolic BP - artery is open most of the time and sounds get quieter

At diastolic BP- sounds disappear

31
Q

Describe automated BP measurements

A

Place cuff on upper arm

Automatically inflated to above systolic BP

Cuff pressure is released

Arterial pulsation causes cuff to oscillate

Oscillations

Digital reading of systolic BP, diastolic BP and mean arterial pressure in the brachial artery

32
Q

Describe blood pressure in the aorta during one cardiac cycle

A

The ventricle ejects blood into aorta (during systole) faster than it can flow away into the periphery. This causes a steep rise in aortic pressure. About 70% of the stroke volume is stored initially in the elastic arteries during systole. Remaining 30% runs off through the runs off through the peripheral vessels.

Max. Pressure in the aorta is the systolic BP = 120 mmHg

As blood runs into the peripheral circulation the aortic BP falls. Minimum pressure in aorta is the diastolic = 80 mmHg

Pulse pressure= SBP- DBP= 120-80= 40 mmHg

33
Q

How do we calculate the mean arterial pressure?

A

The MAP is the mean pressure in the aorta during a single cardiac cycle

Rough approximation:

MAP= P(Dias)+ 1/3P(sys-dias)

More accurately, at the line where area A= area B

Value is about 95 mmHg

The MAP is a critical variable Because it is the average effective pressure that drives blood around the circulation

34
Q

Describe the arterial pressure (pulse) wave

A

Apex beat is hard almost simultaneously with feeling the radial pulse!

When blood is ejected at high pressure into the aorta- a pressure wave is set up which is transmitted along the walls of the arteries

Shape of the pressure wave becomes narrower and taller as it proceeds down the arterial tree

Pressure wave velocity is faster in stiffer (older) arteries

Note: the velocity of blood flow itself is much SLOWER than the pressure pulse wave

35
Q

What factors affect pulse pressure?

A
  1. Stroke volume (pulse pressure inversely proportional to SV)
  2. Arterial compliance: pulse pressure inversely proportional to compliance

Aorta becomes stiffer and less compliant in old age

Elderly: BP 160/80 mmHg

“Systolic hypertension of the elderly”

Don’t confuse arteriosclerosis and atherosclerosis. Arteriosclerosis is a consequence of ageing. Atherosclerosis is plaque formation.

Atherosclerosis = stiffness of the arteries

36
Q

What are the physiological factors affecting blood pressure?

A

Age

Sleep

Exercise (dynamic- increase by 10-40 mmHg, isometric can increase by 100 mmHg)

Emotion/stress (increase BO)

Pregnancy (BP falls)

37
Q

What is the effect of gravity on blood pressure?

A

Pressure foot > heart

Is this in defiance of Darcy’s law Q is inversely proportional to P?

Blood flows against pressure gradient

38
Q

What is the effect of posture on arterial and venous pressures?

A

In the supine position- the entire body is at the level of the heart

Pressure drop of about 5 mmHg between aorta and dorsal is pedis artery in foot. Pressure in foot= 90 mmHg

🔼P = driving pressure

Pressure in veins draining feet is 5 mmHg

Pressure falls to 2 mm Hg at RA

On standing: add the weight of the column of blood (hydrostatic pressure) to BOTH arterial supply of the feet AND to the veins draining the feet

130 cm (in a 1.8 m individual) of blood is = to an extra pressure of 95 mmHg. (This is a hydrostatic pressure)

Arterial pr (in foot)= 90+ 95= 185 mmHg
Venous pr(in foot)= 5+95=100

Driving pressure= 185-100=85(same as in feet of a supinevperson )

As long as there is a pressure difference between arteries and veins- blood will flow

On standing: subtract the weight of the column of blood (hydrostatic pressure) from BOTH the arterial supply of the head AND from the veins draining the head

Subtract 37 mm Hg from the arterial and the venous side

The driving pressure is the same as when recumbent

39
Q

Describe venous pressure

A

Pressure in the venous compartment

Central venous pressure= pressure in thoracic vena cava near RA

CVP is important because it determines filling pressure if RV, and thereby SV through the Frank-Starling mechanism

RA pr is just slightly below CVP

40
Q

What are the factors which affect RAP and CVP?

A
  1. RV contraction is strong: RAP decreased
  2. RV contraction weak: RAP increased
  3. Increased venous return leads to increased RAP

RAP depends on balance between ability of heart to pump blood out into circulation and tendency of blood to flow back into heart

41
Q

Since venous return affects right atrial pressure, what factors affect venous return?

A

Factors that affect CVP and VR
-increased blood volume

-increased venomotor tone
Both increase RAP

Decreased CVP & VR
-hemorrhage

$venidilation

Both decrease Right atrial pressure

42
Q

How does sympathetically induced venkconstriction affect venous return?

A

Sympathetically induced venoconstriction displaces blood from the peripheral veins into central veins and into RA, thus increased venous return

43
Q

How does cardiac failure promote edema?

A

RAP increases (20- 30 mmHg). CVP then increases as well as capillary hydrostatic pressure. Favoring edema formation

44
Q

What mechanical factors that affect venous return?

A
  1. Skeletal muscle pump- contraction of skeletal muscles compresses veins rhythmically

This displaces blood forward toward heart

CVP is maintained, maintaining venous return and EDV
Venous Pr in feet is decreased, because blood drains quickly into the muscle veins (pumping action)

Capillary Pr is decreased in feet and ankles and tendency to form edema is decreased

Remember valves in veins prevent back flow of blood

  1. Respiratory pump
45
Q

Explain how respiratory pump assists in veinous return

A

Respiratory pump-like bellows

Moves chest blood into thorax *physiologically splitting of S2 during deep inspiration

During inspiration: venous return increase to right atrium

On inspiration decreased intrathoracic pressure leads to thoracic veins being expanded. This causes blood from head fills the vena cava. This causes increased flow to vena cava and increased venous return

Another way inspiration increases venous return would be contraction of the diaphragm, leading to increased abdominal pressure, increasing venous return

During expiration: decreased venous return

46
Q

How is blood flow measured?

A

Fick principle

Oxygen extraction

Law of conservation of mass= [O2] pulmonary flow in artery- [O2] pulmonary flow out (veins) come back for exampke

Cardiopulmonary Renal (35 decks)

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