Arterial System
Bioengineering 6000 CV Physiology
Arterial System
Lecture Block 10
Arterial System
Bioengineering 6000 CV Physiology
Vascular Structure/Function
Bioengineering 6000 CV Physiology
Arterial System
Functional Overview
Bioengineering 6000 CV Physiology
Arterial System
Vessel Structure
Endothelium
Elastic tissue
Smooth Muscle
Fibrous Tissue
Arteriole
30 µm
Capillary
8 µm
Venule
20 µm
6 µm
0.5 µm
1 µm
Diameter
Wall
thickness
Aorta
25 mm
Artery
4 mm
Vein
5 mm
Vena Cava
30 mm
2 mm
1 mm
0.5 mm
1.5 mm
Bioengineering 6000 CV Physiology
Arterial System
Aortic Compliance
• Factors:
– age
– athersclerosis
• Effects
– more pulsatile flow
– more cardiac work
– not hypertension
Pressure [mm Hg]
100
200
150
B
lo
o
d
V
o
lu
m
e
[%
]
C =
dV
dP
20--24 yrs
30--40 yrs
50-60 yrs
70--75 yrs
100
300
200
Laplace’s Law
(thin-walled cylinder):
T = wall tension
P = pressure
r = radius
T = P r
=
P r
w
For thick wall cylinder
P = pressure
σ = wall stress
r = radius
w = wall thickness
Tension
[dyne/cm]
Wall Stress
[dyne/cm
2
]
Aorta
2 x 10
5
10 x 10
5
Capillary 15-70
1.5 x 10
5
Arterial System
Bioengineering 6000 CV Physiology
Arterial Hydraulic Filter
Bioengineering 6000 CV Physiology
Arterial System
Arterial System as Hydraulic Filter
• Pulsatile -->
smooth flow
• Cardiac energy
conversion
• Reduces total
cardiac work
Cardiac
Output
Arterial
Pressure
t
t
Physiological
Ideal
Cardiac
Output
Arterial
Pressure
t
t
Pulsatile
Challenge
Cardiac
Output
Arterial
Pressure
t
t
Filtered
Reality
Bioengineering 6000 CV Physiology
Arterial System
Elastic Recoil in Arteries
Arterial System
Bioengineering 6000 CV Physiology
Effects of Vascular Resistance and
Compliance
Bioengineering 6000 CV Physiology
Arterial System
Cardiac Output vs. Runoff
Arterial
Pressure/Flow
Bioengineering 6000 CV Physiology
Arterial System
Basic Pressure Equations
Mean arterial pressure:
which we can
approximate
as
with !
P
s
= systolic pressure
!
P
d
= diastolic pressure
Total peripheral resistance is
If we assume P
ra
=0
with !
P
a
= mean arterial pressure
!
P
ra
= right atrial pressure
!
Q
r
= runoff flow into veins (=Q
h
at equilibrium)
Bioengineering 6000 CV Physiology
Arterial System
Time Course of Arterial Flow
We can estimate change in arterial volume as:
Cardiac
output
Runoff flow
Arterial volume
change
(1)
Which we differentiate w.r.t time to get
(3)
Arterial compliance we define as
(2)
Substituting (1) into (3), we get
or
(4)
(5)
Bioengineering 6000 CV Physiology
Arterial System
Arterial Pressure Response to Cardiac
Output
• Stable pressure
determined by flow and
peripheral resistance
• Increase in CO or R
p
both increase pressure
• Pressure always
changes to force CO to
equal runoff flow
• Compliance affects rate
but not final values
A
rte
ri
a
l
Pr
e
s
s
u
re
Time
Large Compliance
Small Compliance
P
1
P
2
Increase in Q
h
(CO) or R
p
Bioengineering 6000 CV Physiology
Arterial System
Pressure and Age (Compliance)
Pre
ssu
re
Mean Pressure
Bioengineering 6000 CV Physiology
Arterial System
Peripheral Pulse Pressure
• Pressure wave velocity
– v
p
= k/C
– v
p
increases along the
arteries and with age
• Pressure wave pulse
amplitude grows with
distance from heart
– reflection/superposition
– decrease in C
– dispersion
Arterial System
Bioengineering 6000 CV Physiology
Venous System
Bioengineering 6000 CV Physiology
Arterial System
Venous System
• Venous volume
– Large volume, low pressure system
– Reservoir of blood (50% of total volume)
– Blood loss covered by venous system
• Vasoconstriction, drinking (blood doning)
• Venous flow
– Skeletal muscle activity
– Valves
– Breathing
– Paristaltic contractions in venules
Bioengineering 6000 CV Physiology
Arterial System
Venous Valves
• Muscle pump
• Unidirectional flow
• Vericose veins
Arterial System
Bioengineering 6000 CV Physiology
Measurement
Bioengineering 6000 CV Physiology
Arterial System
Measuring Blood Pressure: Catheters
• Liquid column and
external manometer
– frequency response of
transducer and fluid
column
– calibration and zeroing
– motion artifacts
• Manometer-tipped
catheters
– higher frequency
response
– less motion artifact
Bioengineering 6000 CV Physiology
Arterial System
Auscultatory Blood Pressure Method
• Effect of arm position
• Alternate measurement
locations (leg)
• Pressure varies during the
day (lowest during sleep)
• Psychological bias in
measurements (in subject
and operator)
Bioengineering 6000 CV Physiology
Arterial System
Automated Pressure Measurement
Ausculatory
Oscillometric
Bioengineering 6000 CV Physiology
Arterial System
Measuring Blood Flow
• Ultrasound flowmeter
(velocity)
• Electromagnetic
flowmeter (velocity)
• Thermal dilution
• Functional MRI (diffusion
or oxygenation)
Bioengineering 6000 CV Physiology
Arterial System
Measuring Blood Flow II
• Bioelectric impedance
(plethysmography)
• Light (pulse oxymetry)
Finger artery
Bone
Lightproof
casing
Elastomer ring
To device
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