Chapter 4 Flashcards
what are some capabilities for doppler waveform analysis?
a. help confirm diagnosis/ approx location of arterial occlusive disease
b. indicate severity of the occlusive process
c. combined with doppler segmental pressures
What are some limitations of doppler waveform analysis?
a. patients with casts or extensive bandages
b. waveforms may be affected by ambient temp
c. uncompensated CHF may result in dampened waveforms
d. unable to discriminate stenosis from occlusion
e. technically dependent test
what is the patient positioning?
supine with extremities at the same level as the heart. to decrease the influence of HP
the patients hip is externally rotated, knee slightly bent
other positions: RLD LLD or prone
what is the doppler effect?
when a wave is reflected from a moving target, the freq of the wave received is different (doppler shift) from the transmitted wave
why does the doppler effect occur?
occurs with relative motion between the source and the receiver of the sound
what is considered a moving target?
blood
what is considered a stationary source?
the transducer
describe CW doppler
the reflected freq is higher/lower than the transmitted freq, depending on direction of flow
what is a type of doppler velocimetry?
analog
what is an analog?
employs a zero crossing freq meter, to display the signals graphically on a strip chart recorder
what are zero crossing freq meters?
- circuitry counts each time the input signal crosses through zero (the baseline) within a time span
- high freq waves have many oscillations ; low freq waves have few
- direction of blood flow varies during the cardiac cycle
- machine estimates freq present in reflected signal and displays them
what are some drawbacks of analog recordings?
noise, less sensitivity, high velocities are underestimated, low velocities are overestimated
what is spectral analysis?
individual frqs displayed by FFT method
when is spectral analysis more commonly used?
duplex evaluation
on the graph what is displayed on the x and y axis on a spectral analysis?
x=time
y=freq shifts / velocity
T/F spectral analysis has many drawbacks like the analog
false
what transducer is used for spectral analysis?
8-10 MHz
which arteries do you evaluate with a duplex study for UE?
subclav axillary (axilla) brach (antecub fossa)/ elbow radial (wrist, thumb side) ulnar (wrist, 5th finger side)
which arteries do you evaluate with a duplex study for LE?
CFA SFA pop PTA DPA peroneal if necessary at lateral malleolus
what are some potential sources of technical error?
improper probe position inadvertent probe motion incorrect angle of incidence inadequate amount of gel excessive pressure on the probe tip insufficient period of rest before testing
What are more signals considered?
triphasic
what are some characteristics of a triphasic waveform?
rapid upslope sharp peak rapid down stoke flow reversal resumption of forward flow
what vessels are mostly triphasic?
UE, LE
what are come characteristics of a biphasic waveform?
rapid upslope sharp peak fairly rapid downstroke flow reversal no resumption of forward flow also considered normal in some patients
