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FACTORS THAT INFLUENCE THE DOPPLER SPECTRUM
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detect the transit time of the pulse along a known length of vessel. The transit time is given by the delay in the beginning of the pulse detected distally compared with that detected by the proximally positioned transducer (Fig. 6.10). The pulse wave velocity is given by the distance along the vessel between the two transducers divided by the transit time. Measurement of the pulse wave velocity has been used by researchers to study vessel wall elas- ticity changes (e.g., with age or diabetes).
Subjective interpretation
Subjective interpretation of the Doppler spectrum can give many clues as to the level and extent of any disease. For example, changes in the pulsatility of the waveform shape can help to identify disease. The systolic rise time of the waveform is influenced by changes in the cardiac impulse and circulation proximal to the measurement site, whereas the decay of the velocity tends to relate to the distal circulation. Even if these various indices are not quantified, understanding the concept behind them can help when interpreting waveform shapes.
A
B
Transit time
d
Figure 6.10 The pulse wave velocity can be calculated
using two transducers at a distance ‘d‘ apart along the vessel and measuring the transit time of the pulse.
diabetic patient than down the normal artery of a younger person. The pulse wave velocity of a pulse can be measured using two Doppler transducers to
References
Evans D H, McDicken W N 2000 Doppler ultrasound: physics, instrumentation, and signal processing. Wiley, Chichester
Thrush A J, Evans D H 1995 Intrinsic spectral broadening: a potential cause of misdiagnosis of carotid artery disease. Journal of Vascular Investigation 1(4):187–192