Arterial System Bioengineering 6000 cv physiology
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- Bu səhifədəki naviqasiya:
- Endothelium Elastic tissue Smooth Muscle Fibrous Tissue Arteriole 30 µm
- Wall thickness Aorta 25 mm Artery 4 mm Vein 5 mm
- Pressure [mm Hg] 100 200 150 B lo o d V
- 20--24 yrs 30--40 yrs 50-60 yrs 70--75 yrs 100 300 200
- Cardiac Output Arterial Pressure
- Arterial Pressure
- Arterial Pressure/Flow
- Increase in Q h (CO) or R p
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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
Arterial System Vessel Structure
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 =
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
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
Arterial System Cardiac Output vs. Runoff
Bioengineering 6000 CV Physiology Arterial System Basic Pressure Equations Mean arterial pressure: which we can
as
with ! P s = systolic pressure ! P d = diastolic pressure Total peripheral resistance is If we assume P ra =0
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
• Pressure always changes to force CO to equal runoff flow • Compliance affects rate but not final values
Large Compliance Small Compliance
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
– 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
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)
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
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