arterial system lecture block 10sci.utah.edu/~macleod/bioen/be6000/notes/l10-arteries-veins.pdf ·...
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Arterial System Bioengineering 6000 CV Physiology
Arterial SystemLecture Block 10
Arterial System Bioengineering 6000 CV Physiology
Vascular Structure/Function
Bioengineering 6000 CV PhysiologyArterial System
Functional Overview
Bioengineering 6000 CV PhysiologyArterial System
Vessel Structure
Endothelium
Elastic tissue
Smooth Muscle
Fibrous Tissue
Arteriole30 µm
Capillary8 µm
Venule20 µm
6 µm 0.5 µm 1 µm
Diameter
Wall thickness
Aorta25 mm
Artery4 mm
Vein5 mm
Vena Cava30 mm
2 mm 1 mm 0.5 mm 1.5 mm
Bioengineering 6000 CV PhysiologyArterial System
Aortic Compliance• Factors:
– age– athersclerosis
• Effects– more pulsatile flow– more cardiac work– not hypertension
Pressure [mm Hg]100 200150
Blo
od V
olum
e [%
]
C = dVdP
20--24 yrs
30--40 yrs
50-60 yrs
70--75 yrs100
300
200
Laplace’s Law (thin-walled cylinder): T = wall tensionP = pressurer = radius
T = Pr
� =Pr
w
For thick wall cylinderP = pressureσ = wall stressr = radiusw = wall thickness Tension
[dyne/cm]Wall Stress[dyne/cm2]
Aorta 2 x 105 10 x 105
Capillary 15-70 1.5 x 105
Arterial System Bioengineering 6000 CV Physiology
Arterial Hydraulic Filter
Bioengineering 6000 CV PhysiologyArterial System
Arterial System as Hydraulic Filter
• Pulsatile --> smooth flow
• Cardiac energy conversion
• Reduces total cardiac work
CardiacOutput
ArterialPressure
tt
PhysiologicalIdeal
CardiacOutput Arterial
Pressure
t
t
Pulsatile Challenge
CardiacOutput
ArterialPressure
t
t
Filtered Reality
Bioengineering 6000 CV PhysiologyArterial System
Elastic Recoil in Arteries
Arterial System Bioengineering 6000 CV Physiology
Effects of Vascular Resistance and Compliance
Bioengineering 6000 CV PhysiologyArterial System
Cardiac Output vs. Runoff
Arterial Pressure/Flow
Bioengineering 6000 CV PhysiologyArterial System
Basic Pressure Equations
Mean arterial pressure:
which we can approximate as
with ! Ps = systolic pressure! Pd = diastolic pressure
Total peripheral resistance is
If we assume Pra=0
with ! Pa = mean arterial pressure! Pra = right atrial pressure! Qr = runoff flow into veins (=Qh at equilibrium)
Bioengineering 6000 CV PhysiologyArterial 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 PhysiologyArterial System
Arterial Pressure Response to Cardiac Output
• Stable pressure determined by flow and peripheral resistance
• Increase in CO or Rp both increase pressure
• Pressure always changes to force CO to equal runoff flow
• Compliance affects rate but not final values
Art
eria
l Pre
ssur
e
Time
Large Compliance
Small Compliance
P1
P2
Increase in Qh (CO) or Rp
Bioengineering 6000 CV PhysiologyArterial System
Pressure and Age (Compliance)
Pre
ssur
e
Mean Pressure
Bioengineering 6000 CV PhysiologyArterial System
Peripheral Pulse Pressure
• Pressure wave velocity– vp = k/C– vp 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 PhysiologyArterial 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 PhysiologyArterial System
Venous Valves
• Muscle pump• Unidirectional flow• Vericose veins
Arterial System Bioengineering 6000 CV Physiology
Measurement
Bioengineering 6000 CV PhysiologyArterial 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 PhysiologyArterial 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 PhysiologyArterial System
Automated Pressure Measurement
Ausculatory
Oscillometric
Bioengineering 6000 CV PhysiologyArterial System
Measuring Blood Flow
• Ultrasound flowmeter (velocity)
• Electromagnetic flowmeter (velocity)
• Thermal dilution• Functional MRI (diffusion
or oxygenation)
Bioengineering 6000 CV PhysiologyArterial System
Measuring Blood Flow II
• Bioelectric impedance (plethysmography)
• Light (pulse oxymetry)
Finger artery
Bone
Lightproofcasing
Elastomer ring
To device