Vascular A

1
Vascular A P

• Chapter 8
• Characteristics of Arterial Flow

2
Pulsatile Flow

• Intermittent pumping ? variation in pressure
  flow in a pulsatile manner
• Systole
• Greek for shorten
• The first portion of the cardiac cycle
• Diastole
• Greek for to dilate
• Resting half of the cardiac cycle

3
Pulsatile Flow

• Systole
• Early
• Distention of the arteries
• Arterial volume increases rapidly
• Systemic pressure reaches a systolic peak
• Late
• Cardiac ejection decreases
• Outflow via resistance vessels is greater than
  the volume being ejected and pressure decreases
• Diastole
• Pressure continues to decline
• Blood continues to flow from arteries ?
  microcirculation ? tissues

4
Blood Pressure

• Systolic blood pressure
• The force blood exerts against the arterial wall
  during cardiac contraction
• Diastolic blood pressure
• The force blood exerts against the arterial wall
  during maximal relaxation of the heart muscle

5
Laminar Flow

• Laminar - arranged in layers
• Normal within arteries
• Two forms
• Parabolic flow profile
• Bullet shaped
• Each layer travels at a different velocity
• Slowest at the wall
• Fastest at mid lumen
• Plug flow profile
• All layers travel at the same speed

6
Parabolic vs. Plug Flow

• Parabolic flow
• Occurs most notably in a rigid tube
• Noted at peak systole in vessel segments distal
  to the vessel origin, esp. in smaller arteries
• The larger the artery the less likely to occur
• Plug flow
• The larger the vessel the more likely to occur
• Noted at the proximal segment of branch vessels

7
Pressure Wave

• Pressure wave amplitude shape depend on
• Stroke volume
• Ventricular ejection time
• Peripheral resistance
• Arterial wall stiffness
• Increase any of the above ? increase in pulse
  amplitude and pulse pressure (the difference
  between systolic and diastolic pressures)

8
Pressure Wave

• Pressure wave propagation amplitude increase as
  the wave propagates toward the periphery due to
  progressive stiffening of vessel wall and the
  ratio of the wall thickness to the diameter of
  the vessel
• Pressure, mean diastolic show only minor
  changes between the aorta and small arteries
• Distally
• Pressure wave amplitude systolic pressure
  increase due to
• Increasing stiffness of the arterial walls
• Presence of reflected waves

9
Pressure Changes
10
Pressure Changes - Normal

• Brachial pressure approximates aortic femoral
  pressures, therefore it is utilized as the
  standard reference for determination of
  peripheral arterial disease
• Ankle systolic pressures generally exceed
  brachial pressure
• Digit systolic pressures are generally lower than
  brachial pressure

11
Reflective Waves

• Reflective waves arise as vessel diameter and
  stiffness change and branching occurs.
• Late diastole, flow moves forward again as the
  reflective wave encounters resistance of oncoming
  pulse wave. The reflective wave is added to the
  amplitude of the oncoming primary pulse wave.
• Diastolic flow reversal is the hallmark of
  vessels supplying high resistance vascular beds.
• Flow reversal decreases in response to exercise,
  body heating and vessel stenosis.
• Flow reversal increases with vasoconstriction.

12
Pulsatility - Patterns

• Multiphasic with flow reversal
• Triphasic
• Biphasic
• Monophasic
• FLOW REVERSAL occurs primarily due to
• The pressure wave arriving at different
  times in the system
• High peripheral resistance

13
Waveform Morphology

• Reflects blood flow patterns
• Triphasic, multiphasic flow
• Forward
• Reverse
• Forward
• Biphasic Flow
• Forward
• Reverse
• Monophasic Flow
• Continuous forward flow

14
Pressure Changes

• Systolic pressure is sensitive in detecting
  disease
• Waveform changes distal to stenosis/occlusion
• Damping
• Increased time to peak
• Width
• Need to exercise patients with mild disease to
  unmask occult disease

15
Stenosis/Occlusion Effects
16
Flow Changes

• At rest, blood flow may be maintained at
  relatively normal levels in the presence of
  severe stenosis or complete occlusion due to
  development of collateral networks and a
  compensatory drop in peripheral resistance
• Arterial obstruction may alter flow in collateral
  channels leading to possible
• Increased volume flow through the collateral
• Reversal of flow direction, i.e. steal
• Increased velocity
• Alteration of waveform pulsatility

17
Velocity Changes

• Normal, in peripheral arteries, TRIPHASIC
• Sounds may be recognized by listening with
  Doppler
• Distal to arterial stenosis
• Increased velocity, jet effect
• Disturbance to flow, i.e.
• Turbulence
• Spectral broadening
• Varying velocities with eddy formation
• Plug flow
• Dampened waveform, i.e. low amplitude
• Loss of flow reversal
• Audible signals have single component, monophasic

18
Reversed Flow - Disappearance

• Factors include
• Maintenance of relative increased level of
  forward flow due to increased pressure gradient
  across the stenosis
• Resistance created by stenotic lesion
• Decrease in peripheral resistance due to ischemia
• Damping of pressure wave by the lesion ? less
  wave reflection and amplification

19
Effects of Exercise

• Induces peripheral vasodilatation ? decreased
  peripheral resistance
• Flow volume increases to lower extremity vascular
  beds
• Flow volume can increase by 5-10 times that of
  resting volume

20
Resting vs. Exercising Popliteal Arterial Flow
151 ml/min
734 ml/min
21
Vascular A P

• Chapter 9
• Energy Concepts

22
Energy Concepts

• Kinetic energy
• Potential energy
• Fluid energy
• Fluid (total) Energy (FE) sum of
• Potential energy Kinetic energy

23
Kinetic Energy

• Energy of motion
• The ability of blood to do work as a result
  of its velocity
• Small compared to potential energy
• Proportional to
• Mass of blood which is normally stable
• Square of its velocity

24
Potential Energy

• The energy of something at rest
• Main form of energy present in flowing blood
• Combination of intravascular pressure and
  gravitational potential energy

25
Intravascular Pressure

• Components
• Muscular contraction of the heart
• Main component
• Hydrostatic pressure
• Pressure exerted by the column of blood
• Static filling pressure of blood
• Pressure existing due to the relationship between
  the amount of blood in a vessel and the
  elasticity of the vessel walls

26
Hydrostatic Pressure

• Changes with the height of the fluid column
• Equivalent to the weight of the column of blood
  extending from the heart
• In the upright individual it equals 1 mmHg for
  every 1.36 cm, 22 mmHg for each 12 inches, above
  or below the reference point, which in the human
  is the level of the heart
• Supine individual hydrostatic pressure is
  negligible

27
Hydrostatic Pressure
28
Gravitational Potential Energy

• The capacity to do work, based on position above
  a specified reference point
• Higher the object above a point, the greater the
  effect of gravity on the object
• Formula

? specific gravity g acceleration due to
gravity h height above a specified reference
point
29
Dissipation of Energy

• Inertial losses
• It takes energy to overcome the tendency inertia
• Noted as a decrease in the flow velocity
• Viscous losses
• Greater the viscosity of a substance, e.g. blood,
  the greater the amount of energy needed to
  move the blood
• Frictional losses
• Energy dissipation in flowing blood is primarily
  due to friction and the resultant heat
• Loss of energy due to friction between the layers
  of blood
• The smaller the vessel, the greater the
  frictional losses

30
Vascular A P

• Chapter 10
• Arterial Pressure and Flow

31
Flow

• Flow, Volume flow, Flow rate, Q
• The amount of volume moving past a point per
  unit time
• Quantity or amount
• mL, cc, L
• Time
• Second (s), minute (m)
• Total unit
• mL/s or cc/s, L/m

32
Pressure Gradient

• The factor most responsible for flow
• Fluid moves from an area of high pressure
  (energy) to low pressure (energy)
• Pressure gradient
• Difference in pressure between the pressure at
  one end of a tube and the pressure at another
  point in the tube
• ?P P1 P2
• The greater the difference, the greater, or
  faster the flow rate
• No pressure gradient ? NO FLOW

33
Pressure Gradient vs. Q
34
Pressure Gradients vs. Q
35
Poiseuilles Law

• Laws governing pressure, viscosity and flow
• Describes the characteristics of steady, laminar
  flow through a rigid tube without any change in
  the tubes inner diameter
• Can be manipulated to calculate the effect of
• Flow on pressure, and
• Pressure gradient on flow

36
Poiseuilles Law
?
?

• ?P pressure gradient across a segment
• Q flow through the segment
• L length of the segment
• ? viscosity of the fluid
• r radius of the segment

37
Poiseuilles Law Equation

• Defines the relationship between pressure, volume
  flow resistance

Volume Flow (Q) changes occur primarily due
to pressure gradients (P1 P2) and
changes in vessel radius (r) Doubling the
radius ? 16 fold increase in flow Decrease the
radius by 50 ? 95 decrease in flow
38
Resistance Equation
?
?

• Pressure Vs. Flow

?
39
Diameter reduction vs. Pressure gradient
40
Bernoulli PrinciplePressure/Velocity Relationship

• Bernoulli Principle conservation of energy,
  energy is not destroyed, it is transformed
• Bernoulli Equation

41
Bernoulli Principle

• Pressure Velocity Inverse relationship, i.e.,
  ?V ??Pr, ?V ? ?Pr
• Occurs at stenoses, changes in vessel geometry
  abrupt changes in direction

42
Diameter Reduction Calculation
43
StenosisDiameter vs. Cross-sectional Area

• Hemodynamically significant stenosis
• A narrowing of the vessel lumen which results in
  at least a 50 diameter reduction
• Hallmarks
• Focal elevation in the peak systolic velocity
• Post- stenotic turbulence
• Reduced pressure and lower than normal flow
  distal to the stenosis
• Tandem lesions have a more profound effect on
  distal pressure flow than a single lesion of
  equal total length
• Concentric lesion
• 50 diameter reduction corresponds to an
  approximate 75 reduction in cross-sectional area
• 66 diameter reduction corresponds to an
  approximate 90 reduction in cross-sectional area

44
Area Reduction Calculation
45
Reynolds Number

• Reynolds - unitless describes factors
  causing disturbed or turbulent flow
• ?Pr ? ?Volume Flow, but only to a point
• Turbulence develops mainly as a result of
  velocity and vessel diameter change
• Reynolds lt2000 laminar flow
• Reynolds gt2000 turbulent flow
• Turbulent flow ? vessel wall vibration
• Audible bruit
• Palpable thrill

46
Reynolds Number

• Pressure/Flow Relationship

v velocity of fluid q fluid density r
vessel radius ? viscosity of fluid
47
Vascular A P

• Chapter 11
• Mechanisms of Control

48
Cardiac Output

• Cardiac Output (CO)
• The volume of blood being ejected by the heart
  each minute
• General units is L/min
• Normal is 5 L/min
• Determined by two factors
• Stroke volume (SV)
• Heart rate (HR)
• CO SV x HR

49
Stroke Volume

• Stroke Volume (SV)
• The volume of blood entering the aorta with each
  contraction of the left ventricle
• Related to the strength of left ventricular (LV)
  contraction
• ? LV contractile strength ? ? SV and therefore CO
  
• Factors affecting strength of contraction
• Chemical
• Neural
• Mechanical (muscle stretching)
• But only to a point

50
Heart Rate

• Heart Rate (HR)
• Generally reported as beats per minute (bpm)
• Normal average resting HR
• Adult male 70 bpm
• Adult female 75 bpm
• Bradycardia
• A resting HR lt60 bpm
• Tachycardia
• A resting HR gt100 bpm

51
Heart Rate - Determinants

• Pressoreceptors (Baroreceptors)
• Aortic arch
• Carotid sinus
• Stimulation induces a reduction in the HR
• ? pressure ? ? electrochemical impulses to the
  vagus nerve ? ? in HR
• Exteroreceptors
• Nerve receptors in the skin respond to
  temperature
• Cold temperature ? ? HR
• Warm temperature ? ? HR

52
Heart Rate Determinants

• Neurotransmitters
• Chemicals released into the blood during
  emotional states (stress)
• e.g., epinephrine
• ? circulating epinephrine ? ? HR
• Exercise
• Increased level of activity ? ? demand by tissues
  for oxygenated blood ? ? HR

53
Peripheral Resistance

• Regulated by expansion and contraction of the
  arterioles and arterial capillaries
• Neurotransmitters affect nerves within the
  autonomic nervous system
• Baroreceptors
• Chemicals within the blood
• Hypoxia, ? O2 at the tissue level ?
  vasocontraction
• Hypercapnia, ? CO2 at the tissue level ?
  vasocontraction
• Localized ischemia, reduced amount of oxygenated
  blood to a body area ? buildup of metabolic
  byproducts ? vasocontraction
• Causes discomfort, e.g., cardiac angina, visceral
  angina, claudication

54
Peripheral Resistance

• Reactive hyperemia
• Increased blood flow through dilated vessels
  after relief of an obstruction
• Low resistance vascular systems
• Internal carotid artery
• Renal arteries
• High resistance vascular systems
• External carotid artery
• Variable resistance vascular systems
• Vessels supplying the extremities
• Mesenteric vessels

55
Resistance Vessels - Arterioles

• Flow in peripheral arteries is regulated by
  vasoconstriction/dilatation in the resistance
  vessels, the arterioles.

56
Arterioles Resistance to Flow
Arterioles dilate during exercise, body heating,
chemical emotional stimulation in response to
ischemia
57
Normal multiphasic waveform high resistance due
to vasoconstriction distally
58
Pulsatility

• Effect of vasoconstriction and vasodilatation
• Small medium sized arteries
• Vasoconstriction ? increased pulsatility
• Vasodilatation ? decreased pulsatility
• Microcirculation
• Vasoconstriction ? decreased pulsatility
• Vasodilatation ? increased pulsatility

59
Pulsatility
60
Vascular A P

• Chapter 12
• Venous Pressure and Flow

61
Venous Hemodynamics
62
Central VenousNormal Flow Pressure Changes
63
Central Venous Pressure Changes
Central Venous Pressure

• a wave
• Upstroke right atrial contraction
• Downstroke relaxation
• c wave
• Upstroke isovolumetric ventricular contraction
  ? AV valve bulging back towards the atrium
• Downstroke ventricular contraction ? AV valve
  rings pulled toward apex ? relative ? atrial
  volume
• v wave
• Upstroke passive filling of atrium as AV valves
  are closed during ventricular systole
• Downstroke ventricular diastole ? AV valves
  open ? rapid atrial emptying

64
Changes in Venae Cavae Flow vs. CVP

• Two phases of increased flow in the venae cavae
  which correspond to a decrease in the atrial
  pressure
• Pressure in the right atrium decreases as the AV
  valve ring is pulled down, increasing the
  relative atrial volume
• Pressure in the right atrium decreases as the AV
  valve opens, causing volume to leave the
  atrium

65
Changes in Venae Cavae Flow vs. CVP

• Decreased flow in the venae cavae occur as atrial
  pressure increases
• 1. Atrial contraction
• 2. Ventricular systole, before the AV valve
  reopens

66
CVP Peripheral Venous Flow Changes

• Pressure flow changes associated with the
  cardiac cycle
• are not generally noted in the veins of the lower
  extremity
• are generally noted in the large veins of the
  upper extremity

67
Venous Return From the Extremities

• Flow generally occurs from an area of high
  pressure towards an area of relative low pressure
• Pressure changes with respiration are due to
  movement of the diaphragm
• Inspiration diaphragm descends ? ? intrathoracic
  pressure and ? intraabdominal pressure
• Expiration diaphragm ascends ? ? intrathoracic
  pressure and ? intraabdominal pressure

68
Venous Return During RespirationInspiration

• Supine
• Decreased outflow from LE due to increased
  intraabdominal pressure
• Increased outflow from UE due to decreased
  intrathoracic pressure
• Erect
• Increased outflow from LE due to decreased
  intrathoracic pressure and increased hydrostatic
  pressure keeping the IVC distended
• No change in UE outflow

69
Venous Flow Peripheral Resistance

• ? peripheral resistance ? increased venous flow
• Vasodilatation is affected by
• Infection
• Inflammation
• Exercise
• ? peripheral resistance ? decreased venous flow
• Vasoconstriction is affected by
• A need to conserve body heat
• Rest

70
Venous Return During RespirationExpiration

• Supine
• Increased venous return from the lower extremity
  due to decreased intraabdominal pressure
• Decreased venous return from the upper extremity
  due to increased intrathoracic pressure
• Erect
• Decreased venous return from the lower extremity
  due to increased intrathoracic pressure
• No change in venous return from the upper
  extremity

71
Venous Doppler Flow Characteristics

• Spontaneous
• Flow which is present without provocative
  maneuvers
• Generally present in the subclavian, axillary,
  femoral and popliteal veins
• Phasicity
• Flow which varies with the respiratory cycle
• Present only in veins displaying spontaneous flow
  
• Augmented
• Flow which increases after manual compression of
  a distal limb segment
• Pulsatility
• Flow reflecting right heart pulsatility
• Normally noted in the subclavian axillary veins
• Not normally noted in lower extremity veins
• Reflux
• Reverse flow with Valsalva maneuver or in
  response to manual proximal compression
• Venous reflux is never normal

72
Other Pressure Phenomena

• Transmural pressure
• The difference between intraluminal pressure and
  interstitial (tissue) pressure
• Transmural pressure Intraluminal Interstitial
  pressure
• Hydrostatic pressure
• The weight of the column
• The higher the column of blood the greater the
  pressure the column creates

73
Transmural Pressure
Increased Resistance to Flow
Decreased Resistance to Flow
74
Hydrostatic Pressure

• Weight of the column of blood
• Standing 80 mmHg
• Lying 10 mmHg
• Walking 25 mmHg
• Effect on veins
• Increased transmural pressure
• Venous distention
• Increased venous pooling
• Decreased capillary perfusion
• Decreased venous return
• Decreased cardiac output

75
Vascular A P

• Chapter 13
• The Venous Valves and the Leg Muscles

76
Function of the Venous Valves

• Direct venous flow one way, towards the heart
• Prevent venous reflux
• Backward, retrograde, wrong way flow
• Open and close with the action of the muscles
• Contraction of the calf muscles causes the venous
  valves to open, allowing flow to progress upward
• Muscle relaxation allows blood to fall back
  against the valve cusps, closing the valves

77
Muscle Pump - Normal
78
Calf Veno-Motor Pump

• Facilitates venous return to heart
• Reduces the effect of hydrostatic pressure
• Reduces venous pooling
• Is dependent on competent valves and muscle
  contraction

79
Muscle Pump Other Names

• Venous heart
• Calf muscle pump
• Leg muscle pump
• Calf pump
• Muscle pump
• Soleal pump

80
Pathologies Affecting Venous Flow

• Obstruction
• Arterial inflow to the extremity continues but
  venous outflow is slowed or blocked
• Acute
• Chronic
• Venous Valvular Incompetence
• Leads to retrograde filling of the peripheral
  veins