Arterial System Lecture Block 10
Arterial System Bioengineering 6000 CV Physiology
Vascular Structure/Function
Arterial System Bioengineering 6000 CV Physiology Functional Overview
Arterial System Bioengineering 6000 CV Physiology
Vessel Structure
Aorta Artery Vein Vena Cava Arteriole Capillary Venule Diameter 25 mm 4 mm 5 mm 30 mm 30 µm 8 µm 20 µm
Wall 2 mm 1 mm 0.5 mm 1.5 mm 6 µm 0.5 µm 1 µm thickness
Endothelium
Elastic tissue
Smooth Muscle
Fibrous Tissue
Arterial System Bioengineering 6000 CV Physiology Aortic Compliance • Factors: – age 20--24 yrs – athersclerosis 300 • Effects – more pulsatile flow 200 dV 30--40 yrs C = – more cardiac work dP 50-60 yrs – not hypertension
Laplace’s Law 100 70--75 yrs
(thin-walled cylinder): Blood Volume [%] T = wall tension P = pressure T = Pr r = radius
For thick wall cylinder 100 150 200 P = pressure Pr Pressure [mm Hg] σ = wall stress r = radius = Tension Wall Stress w = wall thickness w [dyne/cm] [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
Arterial System Bioengineering 6000 CV Physiology Arterial System as Hydraulic Filter
Arterial Cardiac Pressure • Pulsatile --> Output t Physiological smooth flow t Ideal • Cardiac energy conversion
Cardiac • Reduces total Output Arterial cardiac work Pressure t Pulsatile t Challenge
Cardiac Output Arterial Pressure t Filtered t Reality
Arterial System Bioengineering 6000 CV Physiology
Elastic Recoil in Arteries
Arterial System Bioengineering 6000 CV Physiology Effects of Vascular Resistance and Compliance
Arterial System Bioengineering 6000 CV Physiology
Cardiac Output vs. Runoff
Arterial Pressure/Flow
Arterial System Bioengineering 6000 CV Physiology Basic Pressure Equations
Mean arterial pressure: which we can approximate as
with ! Ps = systolic pressure
! Pd = diastolic pressure
Total peripheral resistance is
with ! Pa = mean arterial pressure
! Pra = right atrial pressure
! Qr = runoff flow into veins (=Qh at equilibrium)
If we assume Pra=0
Arterial System Bioengineering 6000 CV Physiology
Time Course of Arterial Flow
Cardiac We can estimate change in arterial volume as: output Runoff flow
Arterial volume (1) change
Arterial compliance we define as (2)
Which we differentiate w.r.t time to get (3)
Substituting (1) into (3), we get (4)
or (5)
Arterial System Bioengineering 6000 CV Physiology Arterial Pressure Response to Cardiac Output
• Stable pressure determined by flow and peripheral resistance
• Increase in CO or Rp
both increase pressure Increase in Qh (CO) or Rp • Pressure always Small Compliance
changes to force CO to P2 equal runoff flow Large Compliance P • Compliance affects rate 1 but not final values Arterial Pressure Arterial
Time
Arterial System Bioengineering 6000 CV Physiology
Pressure and Age (Compliance)
Mean Pressure Pressure
Arterial System Bioengineering 6000 CV Physiology 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
Arterial System Bioengineering 6000 CV Physiology 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
Arterial System Bioengineering 6000 CV Physiology
Venous Valves
• Muscle pump • Unidirectional flow • Vericose veins
Arterial System Bioengineering 6000 CV Physiology Measurement
Arterial System Bioengineering 6000 CV Physiology
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
Arterial System Bioengineering 6000 CV Physiology 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)
Arterial System Bioengineering 6000 CV Physiology
Automated Pressure Measurement
Ausculatory
Oscillometric
Arterial System Bioengineering 6000 CV Physiology Measuring Blood Flow
• Ultrasound flowmeter (velocity) • Electromagnetic flowmeter (velocity) • Thermal dilution • Functional MRI (diffusion or oxygenation)
Arterial System Bioengineering 6000 CV Physiology
Measuring Blood Flow II
• Bioelectric impedance (plethysmography) • Light (pulse oxymetry)
Finger artery Lightproof casing Bone
To device
Elastomer ring
Arterial System Bioengineering 6000 CV Physiology