Vascular (hemodynamics) Flashcards
(198 cards)
1
Q
Hemodynamics of Occlusive Disease
A
-abnormalities that can occur in the presence of vascular obstruction
2
Q
Are hemodynamics the same for arterial and venous circulation?
A
No.
3
Q
Are arterial and venous walls constructed the same?
A
No.
4
Q
Arterial Walls
A
- thicker tunica media than veins
- greater elasticity
- non collapsable
5
Q
Do arteries have valves?
A
No.
6
Q
What are the pressure systems of arteries vs. veins?
A
Arterial System- high pressure system
Venous System- low pressure system
7
Q
Do veins have valves?
A
Yes.
8
Q
How come when you take blood from a vein, blood does not gush out?
A
- veins have blood under less pressure
- thinner walls
9
Q
Valves
A
- prevent back flow during diastole
- wider diameter
- helps blood get back to heart
- storage for blood
10
Q
Is it possible to return blood as quickly as it leaves the heart?
A
No.
11
Q
What happens to venous valves during systole?
A
- momentum forces valves open
- valves close when momentum decreases
12
Q
What moves blood forward into the Rt atrium?
A
-decrease in thoracic pressure
13
Q
Does the brain have a low or high resistance vascular bed?
A
-low
14
Q
Where are there more venous valves? (prox. or dist.)
A
-distal
15
Q
Pumps in Circulation
A
- heart (primary)
- aortic pump
- muscular venous pump
- respiratory pump
- gravity
16
Q
What does the pumping of the heart mostly affect?
A
-arterial system
17
Q
Partial Vacuum
A
- in Rt atrium during Rt ventricular filling phase
- sucks venous blood flow from IVC to Rt atrium
18
Q
How do the aorta and other elastic arteries store energy?
A
-stretch during each systole
19
Q
The AO acts as a _____ pump.
A
-subsidiary
20
Q
Pressure in Venules
A
16 mmHg
21
Q
Pressure in Great Veins (near heart)
A
4 mmHg
22
Q
What does the muscular venous pump do?
A
-squeezes the veins and propels blood forward (toward the heart)
23
Q
What assists the muscular pump?
A
-venous valves (one way)
24
Q
What does the respiratory pump do?
A
-venous return to the heart
25
What happens with diaphragm motion?
-variations in thoracic and abd pressure
26
Is thoracic pressure lower or higher than atmospheric pressure?
-lower
27
What happens to abd and thoracic pressure during inspiration?
- increase in abd pressure (reduced flow in abd)
| - decrease in thoracic pressure (increased venous flow in chest)
28
Alveoli
- tiny air sacs (1 cell thick)
- in lungs
- at ends of smallest airways
29
What do alveoli exchange?
-oxygen and carbon dioxide
30
How many alveoli absorb oxygen from air?
300 mil
31
What is in close contact with the alveoli?
-PA's and PV's
32
What kind of blood do PA's carry?
-deoxygenated
33
What are the PA's branches of?
-pulmonary trunk (off Rt ventricle)
34
Where do the PV's carry oxygenated blood?
-from lungs to Lt atrium
35
How many PV's are there?
4
36
Diastole
-period of time when the heart (atria) refills with blood after systole (contraction)
37
Ventricular Diastole
-period when both ventricles are relaxing (filling, no contracting)
38
Atrial Diastole
-period when both atria are relaxing (filling)
39
What are the great vessels?
- SVC
- IVC
- PA's
- PV's
- AO
40
Which chamber of the heart does the aorta leave from?
-Lt ventricle
41
What does the thoracic/descending aorta supply?
Thoracic Structures:
- pericardium
- mediastinum
- diaphragm
- esophagus
- bronchi
- intercostal muscles
42
What does the abd aorta supply?
-abdominal viscera with oxygenated blood
43
Azygos Vein
-drains into SVC right before it enters the Rt atrium
44
Which brachiocephalic vein is longer?
-Lt is longer than Rt
45
What does arterial physiology depend on?
-cardiac status
46
What determines blood flow?
- BP
| - peripheral vascular resistance
47
Heart Failure
-cardiac output is insufficient to meet the needs of the body and lungs (Lt and Rt sided failure)
48
Valvular Dysfunction
-prolapsed, vegetations and regurgitation
49
What causes ischemia?
-impaired flow to the Lt ventricle muscle
50
Arrythmias
-irregular heart beat
51
Cardiomyopathy
- problems within the heart muscle
| - thickening and enlargement of chambers
52
Heart Beat
-rhythmic contraction of the heart
53
Heart Rat
-number of times that the heart contracts per minute
54
Internal Pacemaker
-sinoatrial and atrioventricular nodes that initiate he hearts own impulses to contract
55
What is the overall activity of the heart adjusted by?
-nervous impulses in order to serve he body's changing needs
56
What is heart rate controlled by?
-autonomic nervous system (regulates functions below our consciousness)
57
What is the autonomic NS composed of?
- sympathetic component
| - parasympathetic component
58
What do the parasympathetic and sympathetic NS do?
Sympathetic: increases heart rate and force of cardiac contraction
Parasympathetic: decreases heart rate and force of contraction
59
What must be present for a fluid in a closed system to move from one point to another?
-energy gradient
60
In the case of an arterial tree, blood moves because of a ______ ______.
-pressure gradient
61
Which side of the heart has a higher pressure gradient?
-left
62
BP
-force exerted by blood against the arterial walls when the heart contracts
63
What is BP an important indicator of?
- current cardiovascular function
| - risk indicator of future cardiovascular morbidity and mortality
64
What do capillary beds consist of?
- arterioles
- venules
- capillaries
65
each heart beat results in the ejection of approx. ____ cc of blood from each ventricle into the arterial tree.
70
66
What is oscillatory flow in the atrial tree initiated by?
-each beat of the heart (behaves like a flow generator with an ejected pulse)
67
Each heart best pumps approx. ___ml of blood into the atrial system. (causing a BP pulse)
70
68
How many litres of blood is ejected each minute?
5
69
What do the elastic walls of the conducting arteries store?
-excess volume by stretching during systole and relaxing during diastole
70
Where is energy stored during diastole?
-the stretched elastic walls of arteries
71
What is the energy stored in elastic walls used for?
-to propel blood forward through the peripheral resistance vessels
72
Is flow constant in the cardiac cycle?
Yes.
73
When is BP highest and lowest?
Highest- during ventricular systole (contraction)
Lowest- during diastole (filling)
74
Normal BP
120/80
120 is systolic
80 is diastolic
75
Essentail Principal in Circulation
-pressure gradient
76
What produces a pressure gradient?
-contraction of the heart and the resultant ejection of blood into the AO and systemic vessels
77
In circulation, what form is energy lost in?
-heat
78
Vascular Resistance
-resistance to flow that must be overcome to push blood through the circulatory system and create flow
79
Systemic Vascular Resistance (SVR)
-resistance offered by the peripheral circulation
80
What is net flow controlled by?
-arterial and arteriolar resistance
81
In non diseased circulation, the main arteries have large ______ and their resistance to flow is ______.
- diameters
| - small
82
Wha are the main resistance vessels?
-arterioles
83
What is the major determinant of vascular resistance?
-papillary arterioles
84
What kind of vessels are precapillary arterioles?
- autoregulatory vessels
| - dynamically change in diameter to increase or reduce blood flow
85
What is an example of auto regulatory vessels?
-arterioles increase in diameter when exercising to allow for increased flow to muscles
86
Sources of Peripheral Resistance
- blood viscosity
- vessel diameter/radius
- vessel length
87
Blood Viscosity
- resistance to blood flow
| - thickness/stickiness of blood
88
What does viscosity determine?
- friction against vessel walls
- rate of venous return
- work required to pump the heart
- amount of oxygen transported to tissues and organs
89
What affects blood viscosity?
- hypertension
- cholesterol (LDL and HDL), triglycerides
- diabetes
- obesity
- smoking
- males
- age
- temp.
- anemia
90
When does blood viscosity increase and decrease?
Increases- as blood is more hemoconcentrated (rbc concentration increases)
Decrease- as blood is more dilute
91
The greater the viscosity of blood, the larger the ______ will be.
-resistance
92
How does hemodilute (thinner) blood flow?
-more readily
93
How does hemoconcentrated (thicker) blood flow?
-more steadily
94
What is the hematocrit?
-% of rbc's in the total blood volume
95
What does the hematocrit affect?
- blood viscosity
| - resistance to flow
96
The more viscous the blood, the ______ the resistance and the ______ the BP.
- higher
| - higher
97
When will the hematocrit increase or decrease?
Increase:
- more rbc's
- less plasma
Decrease:
- less rbc's
- more plasma
98
What does blood viscosity strongly depend on?
-hematocrit
99
Polycythemia
- abnormal elevation in red cell hematocrit causing high blood viscosity
- increases resistance
- increases work of heart
100
What does anemia cause?
- low hematocrit
| - reduced blood viscosity
101
What happens in low flow states that causes an increase in blood viscosity?
-rbc's stick together
102
What happens in clotting mechanisms are stimulated in the blood?
-platelet aggression and interactions with plasma proteins occur
103
What does clotting cause?
-entrapment of rbc's (increase in blood viscosity)
104
What is an important factor that influences viscosity?
- temperature
| - thickness of fluid
105
What happens when blood gets cold?
- thicker
| - slower
106
What resistance does blood viscosity affect?
-peripheral
107
If there is a greater resistance to flow, what is needed to pump the same volume of viscous fluid?
-greater pressure
108
What has the biggest effect on resistance?
-radius
109
Is there a large pressure change as blood flows from the AO to large vessels?
No.
110
Small arteries and arterioles are the site of ___% of the pressure drop and are the main regulators of SVR (system vascular resistance).
70
111
Which vessels are autoregulatory?
-arterioles
112
What happens to resistance and pressure as diameter decreases?
-both increase
113
What does total vessel length affect?
-peripheral resistance
114
What does increased fatty tissue require?
-more blood vessels
115
What happens to BP and resistance in a longer vessel?
-greater BP and resistance
116
2 Factors that Control Peripheral Resistance
1) sympathetic nerve innervation
| 2) autoregulation (vasoconstriction and vasodilation)
117
Vasoconstriction
-narrowing of a vessel due to contraction of the muscle wall
118
What happens when the smooth muscle found in the tunica media is stimulated?
- vasoconstriction
| - contracts, squeezing the walls of the artery and narrowing the vessel
119
When an after constricts, what happens to the blood flow and the pressure?
- blood flow decreases
| - pressure increases
120
What can be regulated in the body through vasoconstriction?
- body temp.
| - BP
121
Vasodilation
-widening of a vessel, due to relaxation of the muscular wall
122
When a blood vessel dilates, what happens to resistance?
-decreases
123
During exercise, what is required?
-increased blood flow to deliver oxygenated blood to the working muscle
124
Where does vasodilation occur?
-arteriole and capillary bed
125
What vessels are the "stopcocks" of the vascular tree?
-arterioles
126
Where does BP take its biggest drop?
-arterioles
127
What is the principle point of resistance to blood flow in the circulatory system?
-arterioles
128
Autoregulation
-ability of vascular beds to constrict in response to a rise in BP and dilate in reposes to a fall in BP
129
What is reactive hyperemia an example of?
-autoregulation
130
Reactive Hyperemia
- increase in blood flow
- follows restoration of arterial inflow to a previously ischemic limb
- ex. during exercise increase heart rate and vasodilation of arterioles allow more flow to muscular branches
131
Vasoconstriction
- decrease in vessel diameter
| - increase in SVR
132
Vasodilation
- increase in vessel diameter
| - decreases SVR
133
What is high arterial pressure due to?
-high volume of blood in lg and medium sized arteries
134
How is the large volume in the arterial tree preserved?
-maintaining balance between the amount of blood entering and leaving
135
What is the amount of blood entering the arterial tree determined by?
-cardiac output
136
What is the amount of blood exiting the arterial tree determined by?
- arterial pressure
| - total peripheral resistance (dependant on status of microcirculation)
137
What is the driving pressure for flow within a vessel determined by?
- potential energy (generated by Lt ventricular contraction that distends the vessel wall)
- kinetic energy
- pulsatile arterial flow signal is a summation of forward flow from the (Lt ventricle and reverse flow from tidal reflection)
138
What happens when someone has arteriosclerosis?
- arteries become calcified and rigid
- cant expand when the pulse wave of systolic pressure passes through them
- arterial walls experience higher pressure and become weaker
139
Why do we need to know about atheroma?
- develops in arteries and impedes the flow of blood
- evident in spectral doppler
- depends on extent of atheroma present and on the degree of obstruction
140
What type of flow does blood have when it enters a vessel?
-plug flow (no leaders in velocity)
141
What type of flow is in a straight non obstructed tube?
- parabolic (laminar)
- highest flow in centre
- lowest flow at walls
142
What is laminar flow determined by?
-frictional and internal forces between the layers of blood and changes throughout the pulse cycle
143
At a low velocity, fluid flow is ______.
-laminar
144
How is laminar flow characterized?
-motion of fluid along a well defined path
145
What is flow a result of?
-pressure gradient
146
In what way does blood viscosity increase across a vessel in early systole as fluid motion begins?
-uniformly
147
When does turbulent flow happen?
-high velocities
148
Turbulent Flow
- elements no longer travel along well defined paths
- random motion
- irreversible loss of energy
149
What is an example of disturbed flow?
-separation of flow that occurs in vessels with an obvious change in lumen size (ex. carotid bulb)
150
What types of flow may she spectral broadening?
- disturbed
| - turbulent
151
What can disturbed flow indicate?
-pathological change in vessel
152
Where is disturbed flow seen?
At sites of arterial...
- dilation
- curvature
- branching
- bifurcation
153
Why is the pressure drop across a stenosis high?
-as a result of energy loss in the post stenotic region
154
Critical Stenosis
-narrowing of arterial lumen (reduced volume, pressure and flow)
155
Why is there a pressure decrease before a stenosis?
-to allow fluid to accelerate into the stenosis and decelerate out of it
156
What happens to arterial pressure prox. and dist. to a stenosis?
Prox.- higher
| Dist.- lower
157
What is lost distal to a stenosis?
- pressure
| - kinetic energy
158
When atherosclerosis develops, wha compensatory mechanisms come into play to preserve perfusion?
- development of collateral circulation
- local dilation of the affected arterial segment
- increase in the extraction efficiency of oxygen from blood
159
How can flow rate to an organ be controlled?
-degree of constriction of distal arterial bed
160
Types of Flow Waves
- triphasic
| - monophasic
161
2 Types of Vascular Beds
1) low resistance (ex. brain)
| 2) high resistance (ex. muscles at rest)
162
Low Resistance Beds
- brain
- parenchymal organs (kidneys, liver)
- need continuous flow
163
High Resistance Beds
- peripheral circulation (arms, legs and sm intestine when it's not digesting)
- muscles need a high rate of oxygen (especially when exercising)
- low, absent or reversed flow during diastole
164
When is a tripahsic waveform found?
-arteries supplying high resistance peripheral vascular beds
165
3 Components of Flow
- forward flow in systole
- diastolic flow reversal
- forward flow in late diastole
166
What does a biphasic flow wave indicate?
- mild disease if seen in vessel supplying a high resistant bed
- loss of 3rd component in late diastole
167
Monophasic Waveform
- flow is all above baseline
- normally seen in low resistance beds (brain, kidneys)
- abnormal if seen in a vessel supplying a high resistant bed
168
What is the result of tandem lesions?
-large losses of energy at the entrance and exit of lesion
169
What is the result of tandem lesions?
-disturbed flow patterns (jets, turbulence, eddies)
170
How come at rest, the blood flow of a stenosed or occluded vessel may be normal?
- collateral pathways
| - decrease in peripheral resistance
171
How can we measure the severity of occlusive disease? (stenosis/occulsion)
-measure systolic pressure
172
The doppler waveforms have a ______ component (monophasic) rather than the double or triple components usually heard.
-single
173
The monophasic signal occurs only during ______.
-systole
174
Blood Flow in Normal Arteries
- velocity increases to a peak during early systole
| - decreases during early diastole (when flow reversal can occur)
175
What does the shape of the resulting pulse velocity wave reflect?
-pressure gradient
176
Over normal peripheral arteries, double or triple sounds are heard. The second sound represents the diastolic flow ______ (biphasic) and the 3rd sound represents the ___ forward component (triphasic).
- reversal
| - 2nd
177
Velocity Profile
-velocity of blood will vary depending on it's position within the vessel
178
What profile does steady laminar flow demonstrate?
- parabolic
| - ex. CCA
179
Where are max. and min. velocity?
Max.- centre
Min.- wall
180
What is the main parameter for evaluating the severity of carotid stenosis?
-flow velocity
181
How do we ensure the the site of the highest flow velocity has been detected in a stenosis?
-sample through whole area of presumed stenosis until the distal end of plaque is seen
182
Effects of Arterial Stenosis
- widening of band of systolic velocity
- spectral broadening
- complete filling
- reversal of flow (eddies)
183
Alterations in Venous Hemodynamics Occur With:
- change in posture
- competent or incompetent of valves
- effects of venous obstruction
184
What are the 3 main components of venous pressure in the lower limbs?
- hydrostatic (gravitational) pressure
- residual pressure
- muscular and respiratory pressure
185
Hydrostatic Pressure
- due to height of venous blood column
- applies to standing patient
- flow from the furthest point (feet) must return to the Rt atrium
186
In the lower limbs, what is the main resistance to flow due to?
-microcirculation
187
Residual Pressure
-venous pressure supplied by the arterial pressure at the venous end of capillaries
188
Which muscles act as an alternate pump to the heart?
-peripheral muscles
189
The venous valves, like the cardiac valves, establish _______ flow.
-unidirectional
190
Where is the venous response to respiration reversed?
-in the abd
191
What can influence the respiratory changes in blood flow in the upper limbs?
-posture
192
Phasicity
- changes with respiration
| - valsalva manoeuvre affects flow
193
Spontanaity
-flow is most spontaneous closest to heart
194
Spontanaity
- flow is most spontaneous closest to heart
| - flow is readily apparent
195
Compressibility
-veins are compressible due to a thinner muscular wall (can r/o clot this way)
196
What does valsalva do?
- increases intrathoracic and abd pressure
| - decreases or reverses flow in peripheral veins
197
Arterial Hemodynamics
- waveform reflects cardiac cyclce
- not affected by respirations
- high pressure system
- pulsatile
198
Venous Hemodynamics
- waveforms reflect respiratory movements
- phasicity
- low pressure system
- no pulse
