Week 8 hemodynamics (excluding some general)

Question 1

VTI

Answer 1

Velocity Time Integral

Area under the curve of PW or CW

trace and the machine will give the distance that blood travels (mm)

Question 2

Formula to calculate flow (through the heart, valves…)

Answer 2

Q = CSA * VTI

Q is flow in cm^3 or mL
CSA is A = π*r^2, r = diam/2 (diam measured from 2D image)
VTI is velocity time integral

Question 3

Pouseuilles Law (how to calculate flow through body, vessels…)

Answer 3

Q = [ΔP * r^4] / l*n

Q is flow
ΔP is pressure gradient
r is radius
l is length of vessel
n is fluid viscosity

** radius is the most important factor - can change quickly

Question 4

Laminar flow vs. turbulent flow

Answer 4

Laminar flow - flow in layers where fastest flow is in the middle and slowest is by the vessel wall (normal)

Turbulent flow - get turbulence past a stenotic area and kinetic energy is converted to mechanical and heat energy (pathology)
Note: lower press and faster flow through narrow spot

Question 5

Plug vs parabolic flow

Answer 5

Plug - large arteries - all flow is same speed

Parabolic - small arteries - friction plays a larger role and flow is slower by walls and faster in the middle

Question 6

Spectral broadening - when is it normal and when is it not?

Answer 6

widening of peak in spectral display

this is normal in small vessels (bc different velocities bc parabolic flow)

this is abnormal in large vessels (expect plug flow, so spectral broadening suggests atherosclerosis)

Question 7

Peak vel and peak PG

vs Mean vel and Mean PG

Answer 7

Peak - put cursor on peak vel on waveform and machine calculates peak PG too (ΔP = 4v^2)

Mean - trace waveform to get average vel and PG

*in Cardiac, mean PG is more common than peak PG bc more accurate (closer to values from catheterization)

Question 8

AT - defn and what is it used for?

Answer 8

AT = Acceleration Time

time it takes from start of systole (baseline) to the peak of systole

used to assess tardus-parvus waveforms = waveforms that have late and small systolic wave

seen after AS (bc decreased systolic pressure and flow)

Question 9

HR - How can you measure it from doppler waveform?

Answer 9

HR is usually measured from ECG (cardiac) and m-mode (general - measure time from one systole to the next)

HR can be measured from arteriole doppler waveform
- use measurement package
- measure from 1 waveform to the same part of another waveform 2 beats away
- machine will calculate HR = 2/t*60