o_1977r8vv9vk1ts2ms0kd8pksa.pdf

44 D. Maulik
known as the Fourier PI. Subsequently, a simpler version,
the peak-to-peak PI (Fig. 4.12), was introduced
based on the peak systolic frequency shift (S), the
end-diastolic frequency shift (D), and the temporal
mean of the maximum frequency shift over one cardiac
cycle (A):
PI ˆ S
D
A
…5†
Almost at the same time, Pourcelot reported a similar
index, called the resistance index (RI) [23]. It also
gave an angle-independent measure of pulsatility:
Fig. 4.12. Doppler indices derived from the maximum
frequency shift envelope. S peak systolic frequency shift, D
end-diastolic frequency shift, A temporal average frequency
shift over one cardiac cycle. (Reprinted from [30] with permission)
cycle, the ratios are vitually independent of the angle
of insonation.
A unique feature of the uteroplacental, umbilical,
and fetal cerebral circulations is the continuing forward
flow during diastole so the perfusion of vital organs
is uninterrupted throughout the cardiac cycle.
This feature develops progressively in the fetoplacental
circulation. The essential effects of this phenomenon
include not only a progressive increase in the
end-diastolic component of the flow velocity but also
a concomitant decrease in the pulsatility, which is the
difference between the maximum systolic and enddiastolic
components (Fig. 4.13). The pulsatility of
the flow velocity was originally investigated using
Doppler ultrasonography in the peripheral vascular
system.
Gosling and King were the first to develop the pulsatility
index (PI) as a measure of the systolic-diastolic
differential of the velocity pulse [22]. The PI was
first derived from Fourier transform data and is
Fig. 4.13. Concept of pulsatility of an arterial velocity
waveform. Vertical axis represents the velocity magnitude.
Horizontal axis represents the time
RI ˆ S
D
S
…6†
where S represents the peak systolic and D the enddiastolic
frequency shift. Stuart and associates [24]
described a simpler index for pulsatility in which the
numerator is the peak systolic frequency and the denominator
is the end-diastolic frequency shift:
S=D
…7†
where S represents the peak systolic, and D represents
the end-diastolic maximum frequency shift. (Originally,
it was called the A/B ratio). Because the variations
in the end-diastolic frequency shift appear to be
the most relevant component of the waveform, Maulik
and associates [8] suggested the direct use of this parameter
normalized by the mean value of the maximum
frequency shift envelope over the cardiac cycle:
D=A
…8†
There has been a proliferation of indices over the
years. Most of them refer to the pulsatility of the
maximum frequency shift envelope of the Doppler
waveform, but some reflect various hemodynamic parameters,
such as transit time broadening. For obstetric
applications, assessment of the pulsatility and the
end-diastolic frequency shift is of clinical importance.
Comprehensive Waveform Analysis
Attempts have also been made to analyze the Doppler
waveform in a more comprehensive manner. Maulik
and colleagues [2] described a comprehensive feature
characterization of a coherently averaged Doppler
waveform from the umbilical artery (Fig. 4.14). The
measured parameters included the PI and the normalized
systolic slope and end-diastolic velocity. In
1983 Campbell and colleagues [25] reported a technique
for normalization of the whole waveform,
called the frequency index profile. Thompson and as-