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Figure 3. — Portal flow pattern changes during the 
chronic implantation of an ultrasonic probe: velocity 
profile as measured immediately after surgery (left) 
and at one week postoperatively (right). 
Furthermore, the close and constant contact of 
the ultrasonic probe on the vessel is required 
only a short part of the vessel. So, the correct 
position of the transducer is easily obtained, 
v^ithout the complete dissection of the vessel's 
circumference. 
The assessment of the internal diameter of 
the vessel on the echogram avoids the complete 
dissection of the thick nervous plexus surround- 
ing the hepatic artery. On the other hand, the 
use of this actual internal diameter for the 
computation of the blood flow rate is more ac- 
curate than the use of a diameter value sug- 
gested by the size of the ^ow probe, as is done 
in the electromagnetic flowmetry. The con- 
sequent overestimation of the measured average 
blood flow rate in the latter case can be con- 
siderable, only for this reason,^ especially in 
the case of an abnormal and unknown thicken- 
ing of the vessel walls. 
The comparison between the value Qi and Q2 
of the flow rate emphasizes the necessity of a 
flow pattern analysis prior to the computation 
of the volume flow rate. It must be recalled, that 
the accuracy of various techniques used to 
measure instantaneous volume flow rate depends 
on some assumptions about the shape of the 
velocity profile. For example, the linearity of 
the electromagnetic flow measurement is good 
in the case of an axisymmetrical flow pattern. 
In complex flow patterns such as downstream 
from a side to side portacaval anastomosis, 
and in very asymmertical flow patterns such as 
in a curved vessel, such cause of error should 
not be forgotten. The limitations implied by 
the ultrasonic illumination of a single diameter 
only must not be forgotten, nor the errors due 
to the fact that a single ultrasonic transducer 
does not define the direction of the velocity vec- 
tors. Recent development of the method have 
made possible such studies. This problem is par- 
ticularly interesting in complex flow patterns 
such as in the side to side portacaval anasto- 
mosis itself, as suggested by the shape of the 
mean velocity profiles monitored in a sagittal 
and axial plane (Fig. 4) 
Our present data point out the need for a 
non-invasive method of blood flow measure- 
ment. The studies performed within the first 
hours following the completion of the side to 
side portacaval anastomosis on an anesthetized 
and open abdomen dog show only the initial 
evolution of the hepatic circulation changes. 
The implantation of paravascular flow probes 
induces inflammatory changes responsible for 
the marked changes of the flow pattern (Fig. 
3). A catheter tip velocity probe is presently 
under investigation. 
SUMMARY 
A pulsed Doppler ultrasonic velocimeter has 
permitted the studies of blood flows of a qualita- 
tive and a quantitative nature, in normal dogs 
and on an experimental model of the human 
portal hypertension. Blood flow patterns and 
volume flow rates in the portal vein and in the 
hepatic artery have been described before and 
