Biomedical Engineering Reference
In-Depth Information
current motor and mounts the impeller blades and according to Westaby et
al., the noise is very minimal—a problem with other pumps. The adult model
measures 2.5 cm in diameter by 5.5 cm in length and is connected through a
16-mm diameter graft that is 15 cm long. The weight is 85g with a displace-
ment volume of 25 mL. The adult pump is designed to achieve 5 L/min against
100 mmHg pressure at speeds of 10,000. The smaller pediatric version pumps
achieve up to 3 L/min. The pediatric device measures 1.4 cm in diameter by 5
cm in length and is connected through a 10-mm diameter graft that is 10 cm
long; the weight is 18g, and
the displacement volume is 5 mL. If the manufac-
tures says that for optimal mobilization of the patient and freedom
to move,
power can be delivered by two 12-V DC batteries (~10 W-h) for
several hours.
What is that several hours for an adult size? An infant size?
Make sure you include the frictional loss in the calculation [12].
4.32
The Heartmate III [13] is an improved miniature centrifugal pump from its
two previous LVAD models Heartmate 1 and II (made by Thoratec Corpora-
tion, Pleasanton, California). It is supposed to have improved performance
and an extended life. In vitro testing shows that at 135-mmHg pressure, pump
capacity is 7 L/m with an hydraulic efficiency of 30% at 4,800 rpm.
(a) Calculate the power put into the fluid.
(b) Calculate the energy needed for 4-hour functioning of the unit.
(c) If Heartmate II (an axial flow pump) delivers 4 L/m at a 100-mmHg
differential at 10,000 rpm, did the new design meet the intended goal?
Show the calculations.
4.33
A Canadian patient was transplanted with a Novacor left ventricular assist
system (LVAS, WorldHeart Corp.) in Japan and had to be transported back to
Canada for a heart transplant [14]. LVAS is connected in parallel to the natu-
ral circulation and
takes blood from the left ventricle and returning it to the
ascending aorta. The pump typically bears the
entire workload of the left ven-
tricle, but during exercise, native ventricular ejection via
the aortic valve could
occur. Prior to departure, the patient had 112 beats per minute and an output
of 6.7L per minute. To minimize the power consumption, the thresholds were
set for a pump output of 4.0L, a minimum stroke volume of 40 mL, and
a maximum residual volume of 15 mL. If a two-cell pack of Li-ion D-cell
batteries are used (total 30 W-h), was the power sufficient for 21.5 hours of
travel time? By decreasing the capacity, how much power did they save during
the journey? The diastolic pressure to be 80 mmHg, goes a pulse pressure of
