chapter 4: doppler waveform analysis Flashcards
capabilities of doppler
confirm diagnosis and location of arterial disease
indicate severity of occlusive process
limitations of doppler
waveforms can be effected by temperature
uncompensated CHF can dampen waveforms
unable to discriminate stenosis from occlusion
technically dependent
patient positioning
supine with extremities at same level as heart
hip externally rotated
knee slightly bent
doppler shift
when a wave is reflected from a moving target the frequency of the wave returning is different from the transmitted wave
doppler effect occurs with
relative motion between the source and the receiver of the sound
in the doppler shift what is the moving target
blood
in the doppler shift what is stationary source
transducer
types of doppler velocietry
analog
spectral analysis
analog
employs a zero crossing frequency meter
displays the signals graphically on a strip chart recorded
analog paper speed
25mm/sec
zero crossing frequency meter
counts each time the input signal crosses through zero (baseline) within a time span
high frequency waves has many oscillations
low frequency waves have few
machine estimates frequencies and displays them
analog dopller velocimetry drawbakcs
noise
less sensitivity
high velocities are underestimated
low velocities over estimated
spectral analysis
individual frequencies are displayed by Fast Fourier Transform FFT method
spectral analysis is most commonly used
during duplex evaluation
spectral analysis display
time on the X (horizontal) axis and frequency shifts on the Y axis (vertical axis)
upper extremity doppler is performed on which arteries
subclavian axiallary brachial (at elbow) radial (thumb side at wrist) ulnar (5th finger side at wrist)
Lower extremity doppler is performed on which arteries
CFA SFA popliteal PTA (medial malleolus) DPA (top of foot) Peroneal (lateral malleolus)
potential sources of error
improper probe position probe motion incorrect angle of incidence inadequate amount of gel excessive pressure on the probe insufficient period of rest before testing
a complete arterial exam includes
audible and wave form qualities as well as doppler segmental pressures
Normal signals:
triphasic waveform
triphasic waveform characteristics
rapid upslope sharp peak rapid downstroke flow reversal resumption of forward flow
examples of triphasic waveforms
UE and LE arteries
Abnormal signals
biphasic and monophasic waveforms
biphasic waveform characteristics
rapid upslope sharp peak fairly rapid downstroke flow reversal no resumption of forward flow can be considered normal in some patients
monophasic waveform characteristics
slow upslope
rounded peak
slow down stroke
no reversal
a monophasic waveform is often obtained where
proximal to an obstrcution
well collateral occlusions can appear similar to
flow distal to a stenosis
distal to a stenosis waveforms may appear
monophasic and steady
because of vasodilation of distal vessels due to proximal obstruction
subclavian artery signal
high resistance
multiphasic flow
proximal occlusion in subclavian artery wil make the signal
more monophasic
UE Doppler: Strandness and sumner
describe arteriovenous shunts in skin of fingertips that cause flow patterns in hand to be variable
Normal doppler waveform post exercise
pre-exercise wave form qualities are maintained
no reverse component
usually just pressures obtained post exercise
Abnormal doppler waveform post exercise
slow upstroke
rounded peak
slow downstroke
no reverse component
absent doppler signals post exercise may indicate
occlusion or pre-occlusive vessel
analog doppler is not capable of portraying velocities of less than
6 cm/sec
pulsatility index (PI)
calculated by dividing the peak-to-peak frequency difference (P1-P2) by mean average frequency
Acceleration time is based on the principle that
proximal arterial obstruction results in slowing of the time interval between the onset of systole to the point of maximum peak
An acceleration time of >133 msec indicates
proximal iliac disease
inflow disease is
ex: aortoiliac disease
represents blood flowing into the lower extremities
outflow disease is
represents blood flow flowing out into the extremities
ex: femoral-popliteal disease
