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Systems Physiology > Hemodynamics > Flashcards

Hemodynamics Flashcards

1
Q

What is Hemodynamics? What are the four variables that affect Hemodynamics?

A

Hemodynamics- the physics of blood flowing through tubes.
four variables:
1. pressure
2. compliance
3. Convoloicity - how velocity of blood flow is affected by area.
4. Resistance

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2
Q

How do you measure pressure?

A

you measure pressure using mmHg (due to density of Hg liquid. Pressure is what allows LV to move blood through tubes through arterial side back to LA. RV circulate blood to pulmonary circulation to lungs.

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3
Q

What are the two types of pressure used in CV system?

A
  1. blood pressure- pressure that LV produces when it contracts (in vasculature)
  2. Transmural pressure- pressure across the wall
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4
Q

Differentiate between the blood pressure and transmural pressure in a person laying down, vs person standing up.

A

In person laying down: Blood pressure and Transmural pressure are the SAME
In person standing up: blood pressure and transmural pressure DIFFER
- Due to effects of GRAVITY on column fluid in vasculature system, Transmural pressure ABOVE level of heart is LOWER gravity force blood down toward feet) . Transmural pressure BELOW level of heart is HIGHER (due to gravity). but transmural pressure and blood pressure are EQUAL at the heart level.

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5
Q

Where do you place cuff when taking someone’s blood pressure?

A

Cuff placed at elbow, measure transmural pressure pressure at level of heart (index of Bp).
pressure moves blood around system of tubes. Blood flows from higher pressure to lower pressure.

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6
Q

What is compliance used for in CV? When is compliance lowest? Highest?

A

compliance- the change in volume/change in pressure
compliance- characteristic of any hollow organ or vessel (measures how easily chamber expands when filling with volume)
Compliance is lowest when VOLUME in chamber is SMALLEST.
As you fill chamber closer to maximum value, the compliance will be reduced (walls will be stretched)

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7
Q

Describe the level of compliance in vascular system. What is the most compliant part of arterial system. Which vessel is more compliant than this one from arterial system?

A

The compliance of vascular system is NOT the same through out.
Most compliant in arterial system: THORACIC AORTA
VEINS are MORE COMPLIANT than the most compliant part in arterial system. Also most of blood volume is in veins.
Veins can hold a LARGE Volume at Very LOW pressure.
Veins- volume reservoir.

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8
Q

How can you alter the compliance of the veins?

A

Veins- receive sympathetic innervation. If you increase sympathetic stimulation to veins and release NE it will bind to receptors on smooth muscle (alpha 1) and receptor causes contraction of smooth muscle.
This decreases compliance of veins. Makes veins more rigid or less compliant.

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9
Q

How would increasing sympathetic stimulation of veins and decreasing compliance affect overall CV system?

A

if decreased compliance, make wall of vein rigid, pressure would INCREASE in veins, and amount of blood returned to heart would increase.

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10
Q

What happens to Preload if you increase venous return?

A

If you increase venous return, Preload will INCREASE (increase LVEDV) which stretches ventricle close to optimal length, and heart will pump out more volume, hence LARGER SV.
compliance very important on arterial side.

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11
Q

What is venous constriction?

A

Venous constriction is a way of moving blood out of venous reservoir into active circulation and increasing cardiac output.

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12
Q

How does compliance affect arteries?

A

Arteriole compliance affects the SHAPE of vessel

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13
Q

What happens when you increase sympathetic tone to arterial side?

A

increase sympathetic tone, you INCREASE the RESISTANCE in arterioles. This causes blood vessels to constrict and they resist flow of blood and INCREASE pressure in aorta.

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14
Q

How does compliance change as we age?

A

As we get older, our blood vessels get less compliant (less elastic tissue) and arterial side gets less compliant.
individuals in 70s, with less compliant aorta (pressure is 150/70), you will have higher pressure, and wider pulse pressure (difference between systolic and diastolic).

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15
Q

How does cross sectional area affect velocity of blood flow?

A

As you INCREASE cross sectional area, you will DECREASE VELOCITY of flow (INVERSE relationship).

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16
Q

What are the major terms that denote flow in CV system?

A

Q term- Volume flow (m/s)

v- Velocity of flow (distance per unit time; cm/s)

17
Q

What is the largest cross-sectional area in CV system? How does this affect velocity? How is beneficial?

A

MICROCIRCULATION (CAPILLARIES,)- have largest cross-sectional area.
Velocity of blood flow is SLOWEST in capillaries/microcirculation. It is beneficial because capillaries is where diffusion occurs (exchange nutrients and O2). Diffusion works best in large cross sectional area and low velocity of flow.

18
Q

What are the two components in pressure of flowing blood? What happens to components when you increase flow velocity? How does this affect component and blood flow.

A
  1. Lateral (static) component- largest component of total pressure
  2. Kinetic (dynamic) component- smaller component
    Total pressure- lateral and kinetic component combined

At Higher flow velocity, KINETIC compound is much GREATER
and decrease lateral component
Lateral or static pressure that allows blood to flow to tube in organ. Change in velocity of blood flow, reduce lateral pressure and profusion (allow less blood flow) at any organ.

19
Q

How could atherosclerotic plaque affect flow of blood to organs (ex: kidneys)?

A

atherosclerotic plaque produces narrowing of blood vessels, increase velocity of blood flow, reducing lateral pressure and provide less blood flow to kidneys.
Can cause hypertension (as right, left kidney receive less blood for heart)

20
Q

What is aortic valve stenosis?

A

Aortic valve stenosis- narrowing of aortic valve (fused leaflets), and valve cannot open, so Velocity of blood flow will increase which reduces lateral pressure, and reduced blood flow. A patient with this condition could experience ISCHEMIA- reduced blood flow to the muscle, due to change in hemodynamics (blood flowing more faster, lateral pressure reduced, heart gets less blood flow)
aortic valve located between LV and aorta.
normally when heart contracts, aortic valve opens up to allow blood flow out into aorta.

21
Q

What is the role of resistance in CV system? if asked to calculate resistance of entire CV, where would you need to calculate pressure change?

A

Resistance- can be calculated by change in pressure/ flow
R= change in pressure/ Q (flow).
To calculate resistance of whole circulatory system: delta P (change in pressure) = TPR
TPR- change in pressure across the system
so TPR= MABR
Mean arterial blood pressure= diastolic pressure + 1/3 of Pulse pressure= systolic- diastolic
ex: arterial pressure is 120/80.
Calculation:
PP= 120-80 = 40
MABR= 80 + 1/3 (40)= 80 + 13= 93 mm Hg
TPR= Change in pressure/flow
TPR =( mean pressure in aorta)- Right atrial pressure (2mm Hg)
Q= volume flow of systemic (CARDIAC OUTPUT)
CO= HR x SV (normal CO value is 5L/min)
TPR= 93- 2/5 = 18.2

22
Q

What is pulse pressure (PP)

A

Pulse Pressure= difference between diastolic and systolic
PP= Systolic - diastolic
PP= pressure change for each heartbeat.

23
Q

What does resistance primarily dependent on?

A

Resistance is primarily dependent on the arterioles. Depends on whether arterioles are constricted or more relaxed.
changing resistance will affect the pressure, and control flow from arterioles to the capillary.

24
Q

Why are arterioles important?

A

Arterioles are important for regulating PRESSURE (changing the resistance), and regulating VOLUME FLOW from arteries to capillary.

25
Q

What are the variables used to understand pressure-flow relationships and govern flow of fluid?

A

Variables for pressure-flow relationships (Pouisse’s Law)

  • pressure
  • length of tube
  • radius of tube
  • Viscosity of fluid
26
Q

When can you apply Poiseuille’s Law? Does Circulatory system meet this criteria?

A

Poiseuille’s Law- applicable to the flow of fluids ONLY through Cylindrical tubes only under Special conditions:

  1. flow has to be NON-pulsatile (no flow variations with time)
    - however, in circulatory system, flow is pulsatile
  2. Flow has to be LAMINAR
    - flow is not laminar everywhere in circulatory system
  3. Fluid should be a Newtonian fluid (homogenous fluid like water; not suspension like blood)
    - The circuclatory system does NOT meet all criteria to strictly apply poiseuille’s Law but relationships hold true, influence blood flow.
27
Q

Describe the relationship between the 4 variables for flow of fluid?

A

pressure: Greater the change in pressure the Greater the flow (flow and pressure directionally proportional)
no difference in pressure, no Flow
Length of tube: Increase LENGTH of tube, Flow DECREASES
(if tube length doubles, flow decreases by 50%) Inverse
Radius of tube: DOUBLE radius of tube, Flow INCREASES by 16 fold (2^4).
Viscosity of tube: Increase Viscosity, FLOW DECREASES
(inverse relationship; double viscosity, flow decrease by 50%).

28
Q

What is viscosity? When does Viscosity increase?

A

Viscosity- measure of fluid’s resistance to flow (resistance it separate the lamina). force must be applied to overcome viscosity. also describes how thick something is.
Fluid flows faster on center of tube and SLOWER on the periphery
Viscosity is relatively constant in circulatory system , but can change by changing hematocrit (number of RBC’s)
Increase hematocrit (RBC’s), Viscosity increases.
Harder to circulate a more viscous blood around circulatory system.

29
Q

What is polycythemia?

A

Polycythemia- when hematocrit (RBCs) increases to 60-70% and blood viscosity can be 10x that of water. This means more energy is required to move the blood around circulatory system.

30
Q

What is the equation for Poiseuille’s law? In circulatory system, which part of equation varies the most? What is the most efficient way to control volume flow?

A

Q= Pi (pi-p0)r^4/8nl
Q= Volume flow
pi= 3.14
r= radius
l= length
n= viscosity
R^4 power VARIES the most in circulatory system.
When you constrict or dilate arterioles, you are changing the r^4 term.
Dilate the arterioles and Double radius, you INCREASE flow to the arterioles by 16 fold to the organ needed
If CONSTRICT arterioles, decrease radius, REDUCE flow by 16 fold, by changing radius.
Changing radius of a segment of vasculature, is the most EFFICIENT way to control volume flow
altering radius of ARTERIOLES regulate PRESSURE and FLOW to pressure in capillaries.
radius control point in circulatory system.

31
Q

What happens to pressure in aorta if you constrict arterioles?

A

Constrict arterioles, pressure in AORTA will INCREASE, the pressure in the capillaries will DECREASE . This occurs because when you constrict arterioles, You decrease Radius and flow decreases, so pressure in capillary decrease when constrict arterioles.

32
Q

Where does the greatest change in pressure occur in CV?

A

ARTERIOLES- place where the greatest change in pressure, since that is where radius is changed.

33
Q

How are resistors organized in the circulatory system? How does this affect efficiency of blood flow?

A

In circulatory system, resistors are organized in PARALLEL:
all organ beds receive SAME input pressure, but each resistor can respond to either constrict or dilate based on needs of organ.
You can have varying amounts of blood flow going to different organ beds.
Every time you add resistance in parallel, you decrease overall resistance in circuit (now heart does LESS work as you add resistance, more efficient). permits organ beds receive little or no blood flow.
total resistance of parallel: sum of inverse of resistors.

34
Q

What happens when resistors are in Series? How does this affect work the heart needs to do?

A

if Resistors are organized in Series: the total resistance of the circulatory system will be SUM of each individual resistance added together. As you add more organs in series, you increase resistance
More organs in series, greater the resistance, more work heart has to do, greater metabolic demand (less efficient)
for each organ bed organized in series: pressure would be LOWER as you move from R1 to R3, R4, etc.

35
Q

What is the highest pressure during one cardiac cycle? What is the lowest pressure? What is mean arterial pressure

A

Systolic- highest pressure during 1 cardiac cycle (120 mm Hg)
Diastolic- lowest pressure (80 mm Hg)
mean arterial blood pressure= Diastolic + 1/3 PP (pulse pressure)
MAP
Pulse pressure= systolic -diastolic.

36
Q

Does the heart spend more time in Diastole or Systole?

A

Diastole

37
Q

What valve closes at the incisura or dicrotic notch? Differentiate between the aortic pressure pulse in abdominal aorta vs femoral artery.

A

at the incisura point, Aortic valve closes at this area, which marks the end of rapid and reduced ejection phase.
aortic pressure pulse- typical for thoracic aorta.
The aortic pressure pulse Changes SHAPE from thoracic aorta to abdominal and then femoral artery.
The systolic pressure is getting higher as you move away from the heart. The mean pressure stays the same through all three types of artery.
As you move away from the heart, the COMPLIANCE is getting reduce causing change in shape of aortic pressure pulse.
less elastic tissue in walls of abdominal artery and femoral artery, so compliance of aorta decreases as move away from heart which affects shape of pressure pulse.
same stroke volume though.

38
Q

Peripheral flow resistance (systolic, diastolic, and mean arterial pressure) and Volume flow, are affected by changes in what variables?

A

they affected by changes in COMPLIANCE, Total pressure resistance, and STROKE VOLUME
thoracic aorta most elastic (when ventricles ejects sV of blood, aorta stretches, then recoils during diastole).

Systems Physiology (19 decks)

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