Vol.1, No.3, 173-175 (2009) Health
doi:10.4236/health.2009.13028
SciRes Copyright © 2009 Openly accessible at http://www.scirp.org/journal/HEALTH/
Study on regurgitation of a bearing-less mini axial aortic
valvo-pump with closed impeller
Kun-Xi Qian
Institute of Biomedical Engineering, Jiangsu University, Jiangsu, Zhenjiang, China
Received 5 May 5 2009; revised 13 July 2009; accepted 15 July 2009.
ABSTRACT
The back-flow of an aortic valvo-pump will re-
duce the pumping flow rate but can wash out the
gap between the rotor and the stator, and thus
can improve the antithrombogenicity of the de-
vice. To investigate the regurgitation of a 23mm
OD aortic valvo-pump, its closed impeller was
replaced by a cylinder and hereby the valvo-
pump had lost its pumping function. The pres-
sure head crossing the aortic valvo-pump was
maintained by a locally made pulsatile centrifugal
pump, beating rhythmically from 30 to 120mmHg.
The back flow from outlet to inlet of valvo-pump
via the above-mentioned gap was measured.
Results demonstrated that this gap and the
pressure head had remarkable effect on back-
flow; a larger gap and/or a larger pressure head
would lead to a larger back-flow. By 0,20mm gap
and 100mmHg pressure head, the valvo-pump
had ca. 0,8 l/min back-flow. Instantaneous meas-
urement indicated that the back-flow had a pul-
satile form with high rate during diastole while
low rate during systole of the natural heart imi-
tated by pulsatile centrifugal pump. The pump
rotated at 12500rpm, 15000rpm and 17500rpm
respectively, but it was found the rotating speed
had no affection on back-flow. This investigation
provides a basis for pump design seeking for
both increase of the flow rate and improvement
of the compatibility; the former is particularly
important for a mini axial pump and the latter is
extremely difficult for closed impeller.
Keywords: Aortic Valvo-Pump; Regurgitation
Measurement; Different Air-Gap and Pressure Head;
Anti-Thrombogenicity
1. INTRODUCTION
For long-term left ventricular assist, aortic valvo-pumps
were developed [1-4,8], which deliver the blood directly
from ventricle to aorta without connecting tubes and
bypass circle, thus have less dangers of thrombus forma-
tion outside the pump. In the inside of the pump, regur-
gitation can wash out the blood contacting surfaces in the
gap between the rotor and the stator and can prevent the
formation of micro-thrombus thereafter. Regurgitation
will reduce the pumping flow rate, however, it is signifi-
cant therefore to control the back-flow rate to a certain
range by measuring the back-flow and investigating the
factors affecting the back-flow.
2. METHOD
Figure 1 is a schematic drawing of an aortic valvo-pump
with 23 mm outer diameter, in which the impeller is re-
placed by a cylinder. That means the pump has no func-
tion to propeller the fluid from right (inlet) to left (outlet).
Therefore, the flow in the system is only the back-flow
across the gap between the stator and the rotor, and the
flow rate can be easily measured by flow meter. If there is
a pressure head, namely, a pressure difference between
the outlet and inlet of the device, there will be a flow from
outlet to inlet via the air-gap as shown in Figure 1. The
air-gap “S” in Figure 1 between the motor coil and rotor
magnets was made into 0,1mm, 0,2mm and 0,3mm re-
spectively. The pressure head between outlet and inlet of
the aortic valvo-pump was produced to being pulsatile
between 30mmHg～120mmHg by a locally made pulsa-
tile centrifugal pump [5-7] (Figure 2). The valvo-pump
without impeller rotated at 15,000rpm, 17,500rpm and
20,000rpm respectively, in order to compare the back-
flow rate at the different rotating speeds, so as to show the
effect of the rotating speed on back-flow of the aortic
valvo-pump. The back-flow was measured by an Ameri-
can Transonic T110 flow meter; the outlet pressure and
inlet pressure were measured by HP 1205A manometer.
Then the pressure difference between the outlet and the
inlet of the pump was calculated and diagrammed to-
gether with the back-flow value in Figures 3-5. Finally,
the instantaneous back-flow curve was obtained and the
relation between the back-flow and the natural heart
Presented partly at the IEEE Conference on Biomedical Engineering and
informatics. May 2008, Shanghai, China.

K. X. Qian / Natural Science 1 (2009) 173-175
SciRes Copyright © 2009 Openly accessible at http://www.scirp.org/journal/HEALTH/
174
Figure 1. Schematic drawing of aortic valvo-pump (upper).
1. Motor coil; 2.Rotor magnets; 3. Cylinder; 4.Outlet vane.
Lower exhibites a 23 mm aortic axial valvo-pump without
impeller (alternated by a cylinder 3 in Figure 1 upper).
ejection and filling imitated by a locally made pulsatile
centrifugal pump was investigated.
3. RESULTS
The back-flow value was found to be increased along
with the increasing air-gap of the pump and with the
increasing pressure head crossing the device according to
Figures 3-5 The back-flow rate by air-gap 0,3mm is not
appeared in the Figures, because in this case the rotor
vibrated and the measuring became inaccurate. The motor
vibration was due to the bearing-less structure of the
device, the rotor was supported merely by hydraulic force
of the fluid in the gap between the rotor and the stator, it
was not large enough to prevent the rotor vibration in case
of 0,30mm gap between the rotor and stator.
Figure 3 exhibited the back-flow increased from 0,2l/
min to ca. 1,0 l/min when pressure head between outlet and
inlet of the pump increased from 30mmHg to 120mmHg, in
case the gap between the rotor and the stator was 0,20 mm,
at the rotating speed of 15,000 rpm; while the back-flow was
very small if the gap was 0,10 mm, because the re sistance
of the flow was quite large in this case.
Figures 4-5 demonstrated the back-flow at the rotating-
speed of 17,500rpm and 20,000 rpm respectively. There is
Figure 2. Illustration of measuring back-flow of aortic valvo-
pump. 1. Aortic valvo-pump without impeller(alternated by a cy-
linder); 2. Manometers; 3. Flow meter; 4. Locally made pulatile
centrifugal pump.
Figure 3. Back-flow rate of aortic valvo-pump with 0,1 and
0,2mm air gap and 30-120mmHg pressure head at rotating speed
of 15,000 rpm.
Figure 4. Back-flow r ate of aortic valvo-pump with 0,1 and 0,2
mm air gap and 30-110mmHg pressure head at rotating speed of
17,500rpm.
almost no difference among Figures 3-5, indicated ro-
tating speed has no significant effect on back-flow of the
pump.

K. X. Qian / HEALTH 1 (2009) 173-175
SciRes Copyright © 2009 Openly accessible at http://www.scirp.org/journal/HEALTH/
175
175
Figure 5. Back-flow rate of aortic valvo-pump with 0,1 and
0,2mm air gap and 30-110mmHg pressure head at rotating speed
of 20,000rpm.
Figure 6. Instantaneous back-flow curve of aortic valvo-pump
indicates that the back-flow has a high rate(ca,0,9l/min) during
diastole while it is very low(0,4l/min) during systole of the
natural heart.
Figure 6 recorded the instantaneous back-flow curve
of aortic valvo-pump, indicated that the back-flow has a
high rate (ca,0,9l/min) during diastole while it is very low
(0,4l/min) during systole of the natural heart, imitated by
a locally made centrifugal pump.
4. DISCUSSIONS AND CONCLUSIONS
An approach for measuring the regurgitation of an aortic
valvo-pump was presented, and the back-flow of the
author’s valvo-pump was measured. It was found that the
back-flow was affected by the air-gap between the rotor
and the stator, and by the pressure difference between the
outlet and the inlet of valvo-pump; while the rotating
speed of the pump had no effect on pump back-flow.
Larger air-gap or/and higher pressure head resulted in a
bigger back-flow of the valvo-pump. By 0,20mm air-gap
and 100mmHg pressure difference the back-flow reached
0,8l/min. Regurgitation of valvo-pump may reduce the
pump out-flow thus should be limited but can wash out
the blood contacting surfaces both in the motor and in the
pump, thereby can improve the antithrombogenicity of
the device; the former is particularly important for a mini axial
pump and the latter is extremely difficult for closed impeller.
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