What are 2 capabilities of Doppler waveform analysis?
-Help confirm diagnosis/approximate location of disease
-Indicate severity of the occlusive process
Limitations of Doppler waveform analysis
-waveforms affected by ambient temperature
-congestive heart failure (dampened waveforms)
-can't discriminate stenosis from occlusion
Analog doppler velocimetry
Uses a zero crossing frequency meter to display signals graphically on a strip chart recorder
Zero Crossing Frequency Meter
-counts each time the input signal crosses the zero baseline within a time span
-high frequency waves have many oscillations, low frequency waves have few
-Direction of blood flow varies during the cardiac cycle
-Machine estimates the frequencies present in reflected signal and displays them
Drawbacks to Analog (zero crossing) doppler velocimetry:
-High velocities are underestimated
-Low velocities are overestimated
What is spectral analysis?
Individual frequencies are displayed by Fast Fourier Transform (FFT) method.
-more commonly used during duplex evaluation
-Time: x-axis; Frequency shift: y-axis
Where are doppler waveforms taken in UE?
Brachial (AC fossa)
Where are doppler waveforms taken in LE?
(Peroneal, if necessary)
Potential sources of technical error in doppler waveforms:
-incorrect angle of incidence
-inadequate amt of gel
-excessive pressure on probe tip
-insufficient rest before testing
Features of Triphasic waveform
-resumption of forward flow
(i.e. UE, LE arteries)
Features of Biphasic waveform
-fairly rapid downstroke
-no resumption of forward flow
(also considered normal in some pts)
Waveforms distal to an obstruction are:
monophasic, more steady
(less resistive due to vasodilation)
Normal doppler waveforms post-exercise
-Pre-exercise waveform qualities are
maintained and/or augmented
-No reverse component
(normally just pressures are taken after exercise, not waveforms)
Abnormal doppler waveforms post-exercise
-more rounded peak
-no reverse component
What factors are used in Quantitative (number) evaluation of doppler waveforms?
Pulsatility index and Acceleration time both help to differentiate:
Inflow (aortoiliac) disease from outflow (femoral) disease
Acceleration time in arterial obstruction is the:
slowing of time between the onset of systole to the point of maximum peak.