RIU 324 Lecture Notes - Lecture 42: Pulsatile Flow, Windkessel Effect, Blood Pressure

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I. Velocity and Flow Changes with Percentage Stenosis
A. Notice that the volumetric flow is maintained for percentage
decreases in cross-sectional area up to about 75%. Past
75%, the volume begins to drop rapidly. Notice that as the
percent stenosis increases, the velocity increases to maintain
the volumetric flow. Eventually, the increased energy loss
related to frictional and viscous losses dominates and the peak
velocity decreases precipitously.
B.
II. Arterial or Pulsatile Flow
A. Systole is when heart is fully contracted = max. Pressure.
Conduit vessels are large and a change in diameter doesnt
change the flow rate (increase velocity to
compensate).Resistance vessels are small (< 1 mm). Small
changes in diameter = large changes in volumetric flow.
B. Windkessel effect (or compliance) in Resistance vessels
C. Compliant vessels expand & contract to extend flow
D. Pulsatile flow in compliant vessels thus includes forward flow
and/or flow reversal in diastole, depending on location within
arterial circulation.
E. Pressure gradually decreases from the arterial to the venous
circulation
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F.
G. Total fluid energy content of blood decreases as it moves
through the circulation. Dissipated by frictional losses
III. Pulsatility Index
A. PI is used to describe velocity changes during the cardiac cycle
B. Large differences in velocity from systole to diastole yield a
large PI
C. Velocity is highly variable depending upon location and exercise
1. Exercise causes vasodilation in lower limbs
2. Results in lower resistance
3. Antegrade flow is present during both systole & diastole
4. Influenced by obstruction, aneurysm, arteriovenous
fistula, and vasospasm
D. High PI Low PI
E.
F. Peak-to-peak frequency
G. mean
H. PI generally increases from central to peripheral vessels
I. PI will be decreased after a hemodynamically significant
stenosis
J. Distal arteries will have the highest PI (i.e. Radial Artery)
IV. Systolic Acceleration and Pressure
A. Step 1:Relate pressure with volume change.
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