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a Chapter 5 Venous Hemodynamics 59
that the velocity pulsation of the Doppler recording
incompletely describes the pulse wave, excluding such
information as variation in volume or cross section,
pressure, pulse velocity and direction.
Cardiac Function and Waveform
Fig. 5.4. Estimated spatial velocity distribution at the umbilical
vein±ductus venosus junction based on a computer
model. The velocity increases before the blood has reached
the narrow entrance of the ductus venosus. The high axial
velocity is maintained for a longer distance compared with
the peripheral velocities that are reduced with the growing
cross section along the vessel (see also Figs. 5.2, 5.3). (From
[32])
Fig. 5.5. Blood velocity recorded at the isthmus of the
ductus venosus at 12 weeks of gestation (left). During atrial
contraction the velocity shows a deflection below the zero
line (a), but at the same time retaining some antegrade velocity
(arrow). The reason could be that the velocity profile
across the vessel cross section at this moment is transformed
and contains both antegrade and retrograde velocities
(right)
traced and what is actually defined as the minimum
velocity during atrial contraction.
Pulsation in Veins
Venous pulsation observed during ultrasound Doppler
recording is commonly used for diagnostic purposes.
It is a regularly repeated velocity increment or
inflection; however, it is worthwhile to keep in mind
The waveform of the venous pulse is determined by
the function of the heart. Usually there is a systolic
peak (during ventricular systole), a diastolic peak
(during passive filling of the ventricles) and a diastolic
nadir (reflecting the atrial contraction; Fig. 5.6).
The more energy put into the pulse, the further out
in the system it will reach. That is particularly obvious
during atrial contraction. The Frank-Starling
mechanism causes an augmented contraction in a
distended atrium during fetal bradycardia, and the
wave propagating along the veins reflects that. A particularly
strong atrial wave is seen in cases of arrhythmia
when atria and ventricles happen to beat
simultaneously. An augmented atrial wave is also seen
in cases with increased afterload and adrenergic drive
during hypoxemia [18±23]. Although the atrial contraction
wave is the most commonly used sign for
cardiac function, there is additional information hidden
in the waveform [24, 25].
The smooth systolic peak of the wave of a precordial
vein also reflects a normal compliance of the
heart. External constricting processes (e.g. high-pressure
pleural effusion; Fig. 5.6), particularly a stiffer
and less compliant myocardium (e.g. hypoxia, acidosis,
cardiomyopathy), gives a quick rise in pressure
during systolic filling of the atrium, and a corresponding
steep downstroke of velocity resulting in
the more pointed systolic peak velocity (Fig. 5.6) [26,
27]. A quick rise in atrial pressure is sometimes
caused by a significant tricuspid regurgitation leading
to a similar but less acute downstroke during systole.
Reduced compliance of the myocardium is not
only reflected in the acute downstroke of the systolic
peak but also in the dissociation of the systolic and
diastolic peak (Fig. 5.6). The dissociation between the
systolic and diastolic peak seems to be a late and
ominous sign of myocardial compromise [27, 28].
Transmission Lines
The pulse generated in the heart is not transmitted
equally well in all tissues. It travels better along
transmission lines, and arteries and veins connected
to the heart constitute such transmission lines.
A discontinuation of the transmission line affects
the pulse propagation and deprives the venous waveform
of its usual details [27, 29]. If the pulmonary vein
is not connected to the left atrium but to the portal system,
the pulse recorded in the vein no longer reflects