Circulation And Hemodynamics Flashcards
1
Q
What is
Cardiac Output?
A
Rate at which blood is pumped from either ventricle
2
Q
What is
Venous Return?
A
Rate at which blood is returned to atria from veins
3
Q
What will CO equal in steady state?
A
VR
4
Q
How is the CO of the Left Heart distributed among organ systems?
A
Via set of parallel As.
5
Q
What percentage of CO is distributed and to where?
And thru what As.?
A
15 % —> brain via cerebral as.
5% —> heart via coronary As.
25% —> kidneys via renal As.
6
Q
How can you change blood flow to an organ system? (3)
A
- CO = constant, by blood flow redistributed
- CO = increases or decreases, % distribution = constant
- both CO and % distribution
7
Q
What are the characteristics of
Arteries?
A
- under high pressure
- small percentage of the blood volume
- Thick walled w/ extensive development of elastic tissue, Sm. M., and CT
- contain the Stressed VOlume
8
Q
What is Stressed Volume?
A
Volume of blood in arteries
under High Pressure
9
Q
What are the characteristics of Arterioles?
A
- moderate pressure, smooth muscle walls can contract to control flow
- SM m. In walls
-innerv. By Symph. Adrenergic w/
Alpha-1 Rs.=will constrict
-Beta-2 = will dilate
10
Q
What are the characteristics of veins?
A
- under low pressure
- contain largest percentage of BV
- contract to move blood to As. To increase BP
-have UNstressed volume
11
Q
What is unstressed volume?
A
Volume of blood in veins (bc blood is under low pressure)
12
Q
What are the characteristics of capillaries?
A
Interposed b/w arteries and veins
Large x-sect. Area
Single endothelial lining
X-change of nutrients, waste, and fluid occurs across cap walls
13
Q
What is the formula for the
Velocity of blood flow?
A
V = q/a
14
Q
How will velocity change as diameter increases?
A
Velocity decreases
15
Q
Why is velocity lowest in the capillaries?
A
Bc caps are highest in cross-sect.
16
Q
What will increased viscosity due to velocity?
A
Increase viscosity = decreased velocity
Bc increased resistance —> decreased flow —> decreased velocity
17
Q
What are murmurs?
A
Audible vibrations caused by turbulent flow
18
Q
What is the velocity of blood flow showing?
A
Rate of displacement of blood per unit of time
19
Q
What 2 factors determine blood flow?
A
- Pressure difference
2. Resistance
20
Q
What is the formula for
Blood flow?
A
Q = change(P) / R
21
Q
What will happen to Q as resistance increases?
A
Decreased flow
22
Q
How would you solve for resistance of entire systemic vasculature or in a single organ/blood vessel?
A
R = change (P) / Q
23
Q
What is total peripheral resistance?
A
Resistance of entire systemic vasculature
24
Q
What is the formula for
Total peripheral resistance?
A
TPR = (Paorta - Pvena cava) / CO
25
What does the Poiseuille equation determine?
Determines resistance to flow and its relationship to blood vessel diameter and blood viscosity
26
What is the poiseuille equation dependent on?
If blood flow is sequential or in parallel
27
What is the formula for
Resistance to Blood flow?
R = 8nl / (pi)(r^4)
```
n = viscosity of blood
l = length of blood vessel
```
28
How would an increase in viscosity occur?
Hematocrit increase
29
How much would resistance increase with 75% occlusion of artery?
Resistance increase by 256 fold
Bc 1/ (1/4^4) = 256
30
What is “series” resistance in blodo vessels?
How would you then calculate R?
‣ Total resistance of system arranged in series = sum of individual resistance
• R(total) = R(artery) + R(arterioles) + R(capillaries) + R(venules) + R(veins)
31
In series, how is flow and pressure affected?
Flow is the same at each levels
Pressure will decrease
32
Where is the greatest decrease seen in a Series system?
In arterioles bc they contribute the largest portion of resistance
33
Where is parallel resistance seen?
In major arteries branching off aorta (renal, cerebral, coronary)
34
How is the total resistance in parallel compared to individual resistances?
Total resistance is much less
35
What is the formula for
Parallel Resistance ?
1/R(total) = 1/(R1) + 1/(R2) + 1/(R3) etc.
36
How is the flow and pressure affected by Parallel Resistances?
Flow is decrease, but pressure is not lost
37
If resistance of one vessel in parallel increases, how is total resistance affected?
Total resistance increases
38
What is laminar flow?
What is the velocity at the
Vessel wall &
Center?
Streamline flow with a smooth parabolic profile
Velocity at vessel wall = center
Velocity at center = maximal
39
What is turbulent blood flow?
Streams are mixed radially and axially and energy is wasted
40
What will turbulent flow cause?
Audible flow w/ Korotkoff sounds or murmurs
41
What are some causes of turbulent flow?
Blood vessel stenosis
CV disease
42
What is the Reynolds number used for?
To predict whether blood flow will be laminar or turbulent
43
What is the formula for Reynold’s number?
N = pdv / n
```
p = density
n = viscosity
```
44
If Reynolds # is less than 2000 - what kind of flow is it?
Laminar
45
If Reynolds # Is over 2000 - what kind of flow is it?
Turbulent
46
If viscosity decreases how is Reynolds # affected?
Increased
| Moving toward turbulent
47
If the diameter of the vessel narrows, how is Reynolds # affected?
Increased
| Moving toward turbulent
48
What can Anemia cause?
Functional murmurs bc turbulent flow
| Bc decreased hematocrit = decreased viscosity = increased Reynolds #
49
How do Thrombi affect Reynolds #?
Blood clots will narrow vessel diameter and increase blood velocity
—> increase in Reynolds #
50
Why is the mean pressure high in the aorta? (2)
1. Large volume of blood pumped form LV
| 2. Low compliance of arterial wall
51
The pulsatile pressure seen at the aorta reflect what?
Pulsation activity of heart
| Ejection of blood during systole, resting during diastole
52
Where will pulsing pressures stop being seen?
In arterioles
53
What is the formula for pulse pressure?
Systolic - diastolic
54
How does compliance affect pulse pressure?
Why?
Increases it
Bc systolic pressure increases (need higher pressure to pump out), but diastolic stays the same
55
What is the mean arterial pressure?
Average pressure in complete cardiac cycle
56
What is the formula for
Mean arterial pressure (MAP)?
MAP = Diastolic + 1/3 (Pulse pressure)
57
What is arteriosclerosis?
• Build-up of plaque deposits in arterial walls decrease diameter of arteries and make them stiffer and less complaint
58
How does arteriosclerosis affect
- systolic pressure
- pulse pressure
- mean pressure?
Systolic = increased
PUlse pressure = increased
Mean pressure = increased
(Will not change shape)
59
How does aortic stenosis affect MAP?
Narrowed aortic valve = less SV from LV to aorta
= systolic p. = decreased
= pulse p. = decreased
= mean pressure = decreased
60
How does pressure in the pulmonary vasculature differ from systemic?
Lower than systemic
61
How is Venous pressure?
Low pressure, high compliance, large volume
62
How is atrial pressure estimated?
By pulmonary wedge pressure
63
What does the pressure at the Left atrium determine?
Extent of cardiac failure
| We measure there bc if there is no blood/pressure there = no blood out to body
64
What does the compliance of blood vessels mean?
Volume of blood a vessel can hold at a given pressure
65
What is the formula for
Compliance of Blood vessels?
C = V/P
66
What happens to compliance w/ age?
Less compliant w/ age bc..
Arterial walls become stiffer and less distensible
67
For an old artery to hold the same volume as a young artery, how should the pressure be?
Much higher in old than young
68
What is microcirculation?
Refers to function of the smallest blood vessels (caps and neighboring lympahtic vessels)
69
What is the function of capillaries?
‣ Sites of exchange of nutrient and waste products in tissues and site of fluid exchange b/w vascular and interstitial compartment
70
What is the flow from arterioles to caps?
Arterioles —> meta-arterioles —> capillaries
71
What are precapillary sphincters?
| What is their function?
Band of Sm. M.
Open and close and determine blood flow to capillary bed
72
How does exchange occur across cap walls?
By simple diffusion
73
What does the rate of diffusion thru/between cap cells depend on?
```
Driving force (partial pressure)
Surface area available
```
74
How does water soluble substances get across cap walls?
Diffuse in the aqueous clefts between endothelial smells
• So, surface area for their diffusion = less than that for the lipid soluble gases
75
What are the factors for fluid transfer across Cap Walls?
Osmosis driven by
1. Hydrostatic pressure
2. Osmotic pressure
76
How can proteins cross into caps?
Thru fenestrated caps or in pinocytotic vesicles
77
What is the effective osmotic pressure contributed by protein in Caps called?
Colloid osmotic pressure or
ONCOTIC pressure
78
What does the Starling equation tell us?
Fluid movement across capillaries
79
What is the formula for the
Starling Eq. ?
J = Kf [(pc + (pi)i)] - [(Pi + (pi)c)]
80
What if Kf in the starling equation?
Hydraulic conductance (mL/min per mm Hg)
‣ Water permeability of the capillary wall
81
What is Pc in the Starling Eq.?
Capillary hydrostatic pressure (mm Hg)
‣ force favoring filtration out of capillary - favors out
82
What is Pi in the starling Eq.?
Interstitial hydrostatic pressure (mm Hg)
‣ Force opposing filtration out of capillary - favors in
83
What is (pi)c in the starling Eq.?
Capillary oncotic pressure (mm Hg)
‣ Force opposing filtration out - favors in
84
What is (pi)i in the starling equation?
Interstitial oncotic pressure (mm Hg)
‣ Force favoring filtration- favors out
85
What are the characteristics of lympahtic capillaries ?
lie close to vascular capillaries
◦ Have one way flap valves - permit interstitial fluid and protein to enter but not leave capillaries
86
What will the lympahtic capillaries merge eventually into?
The thoracic duct
87
How is lymph pushed back to Thoracic duct?
Compression of lymph vessel by activity of surrounding sk. M.
And
by contraction of smooth m. In lymph vessels
88
How many liters of lymph are recycled/day?
2-3 liters/day re-enters at subclavian v.
89
What is Edema?
Increase in interstitial fluid volume
90
How is edema formed? (2)
When there is increased filtration
Or
When lympahtic drainage is impaired
91
How can Pc cause increased filtration?
If Pc is increased ==> increased filtration (favors out)
Increased if elevated venous pressure (heart failure)
92
How can pi(C) cause increased filtration?
```
Decrased pi(c) ==> increased filtration
(Favors in so you would want it to decrease)
```
Decrease due to decrease in albumin due to starvation or liver failure
93
How can Kf cause increased filtration?
If increased
Can be increased due to
- cap wall destruction
- burn
- inflammation (release of histamine, cytokines)
94
How does Pi increase filtration?
If restricted = increased filtration
| Pi favors in so you would want it decrased
95
How can lymphatic drainage be impaired and what would this lead to?
Would lead to edema
Impaired due to...
- removal or irradiation of lymph nodes
- standing (no sk. M. Compression of lymphatics)
- parasite infection of lymph nodes
96
How does sympathetic control alter resistance?
Can stimulate resistance beds and increase it
97
What is local control of circulation for?
Primary mechanism is utilized for matching blood flow to the metabolic needs of a tissue
98
What vasoactive substances have effects on circulation?
Histamine and bradykinin = vasodilation of arterioles
99
What are the 3 ways local control of blood flow occurs?
1. Auto-regulation (myogenic)
2. Active hyperemia
3. Reactive hyperemia
100
What is autoregulation in local control of blood flow?
What organs use this mechanism?
‣ Maintenance of constant blood flow to organ in face of changing arterial pressure
```
‣ Organs who do this:
• Kidney
• Brain
• Heart
• Skeletal m.
```
101
What is the myogenic hypothesis?
• When vascular smooth muscle is stretched, it contracts.
Thus if arterial pressure is suddenly increased, arterioles are stretched and sm. M. Will contract in response
• Contraction causes constriction —> increased resistance —> constant blood flow
102
What is Active hyperemia in Local control of blood flow?
Metabolic control
‣ Blood flow to an organ is proportional to its metabolic activity
103
What metabolites have to increase their interstitial concentration, in order for the metabolic rate to increase?
What one will decrease and cause icnreased metabolic rate?
CO2
H+
K+
Lactate
Adenosine
(O2 - decreases)
104
How does an increased metabolic rate affect local control of blood flow?
‣ Causes Sm. M. Of Arterioles, metarterioles, and pre-capillary sphincters to relax —> increase flow thru arteries
105
What is an example of active hyperemia?
Strenuous exercise
106
What is reactive hyperemia in the Local control of Blood flow?
‣ Increase in blood flow in response or reacting to a prior period of decreased blood flow
* When a vasuclar obstruction causes build of of metabolites leading to vasodilation
* When obstruction is remove, area is filled with blood
107
What is an example of reactive hyperemia?
When you sit on your hand
108
What is coronary circulation most sensitive to?
PO2 and adenosine
109
What is cerebral circulation most sensitive to?
PCO2
110
What is ANP?
Vasodilator that is secreted by atria in response to increased atrial pressure
111
What are the effects of Angiotensin II and Vasopressin?
VasoCONSTRICTORS that increase TPR
112
What is the metabolic hypothesis?
‣ O2 delivery to a tissue can be matched to O2 consumption of tissue by altering resistance of Arterioles, in turn altering blood flow
‣ As a result of metabolic activity,
• Tissue produce various vasodilator metabolites
◦ CO2, h+, K+, lactate and adenosine
113
What is shear?
◦ Consequence of fact that blood travels at different velocities w/in blood vessel
(If at same velocity - no shear)
114
Where is shear highest at?
At blood vessel wall
115
Where is shear lowest at?
Center of blood vessel
116
How does shear contribute to vascular tone?
Dilation of vascular bed due to metabolic demand = increased flow
—> increased shear —> release of NO
NO causes to vasodilation and AUGMENTS DOWNSTREAM METABOLIC EFFECT
117
What is the only method that reacts to downstream needs?
Example?
Shear
‣ Downstream there is a buildup of metabolites —> signals to vasodilates
‣ Vasodilation causes increased blood flow thru arteries prior to blockage
‣ This increase will increase the shear experienced
‣ Increased shear causes release of NO
‣ NO causes vasodilation
• Augmenting the downstream metabolic effect
118
What is cerebral circulation largely controll by?
By local metabolites (esp. CO2)
119
What does hypoxia cause re: vascular tone?
Vasoconstriction in pulmonary circulation
120
How is renal circulation controlled?
What is it independent of?
Tightly AUTO-regulated so that flow remains constant even when renal perfusion press. Changes
Independent of sympathetic innervation
121
What control is Sk. M. Under -
At rest?
When active?
During flight response?
At rest: central baroreceptor control (ne —> Alpha)
Active: under local
(Vasodilator substances)
Flight: Adrenal —> epi —> beta-2 = vasodilation
122
How is COronary circulation affected by mechanical compression?
Mechanical compression will occur during systole in cardiac cycle
- causes brief period of occlusion and reduction of blood flow
- reactive hyperemia occurs
- increased blood flow post systole
123
What is Skin circulation controlled?
Sympathetic vasoconstriction according to baroreceptor reflex
124
How is Skin circulation changed when there is excessive body temp.?
Sympathetic inhibition
-dilation of shunt pathways
125
What are the Shunt pathways?
Examples of each?
1. R —> L
- blood passes from systemic Vs. —> As. W/o passing thru functional lung tissue
2. L —> R
- blood from Systemic As. —> VSD. W/o passing thru cap bed
