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Artificial Heart Valve
Turbulence
Measurement Device
Team #7
Sarmad Ahmad Hillary Doucette Stephen Kustra
Background
Blood Composition
Hemoglobin
Hemoglobin is an iron containing protein necessary for oxygen transport in the blood
Hemoglobin is found inside red blood cells, and due to its iron constituent, is responsible for the cells’ deep red tone
Blood Plasma
Blood plasma is the solution in which blood cells are suspended
Blood plasma consists of proteins, blood clotting factors, mineral ions, carbon dioxide, glucose, etc.
After filtration, blood plasma is typically translucent and yellow in tone
Free Hemoglobin
When red blood cells rupture (hemolysis), hemoglobin is released into the blood plasma
Due to the distinctive color of hemoglobin, free hemoglobin in the blood can easily be detected by the reddening of the blood plasma
In this blood turbulence monitor, free hemoglobin will be the key factor in determining the amount of turbulence in the blood created by artificial heart valves.
Description
This system measures the turbulence
generated by an artificial heart valve by
measuring the levels of free hemoglobin
released from the ruptured red blood cells
downstream.
Device Requirements
The device must meet the following requirements.Must have variable flow rate for re-circulated blood
sample
Must be able to put commercial heart valves in-line for testing
Must be able to display clotting factors and flow rate
Must design a pump for the closed loop system that will minimize stress on RBCs
Must be able to work with actual blood as fluid
System must maintain homeostasis for accurate results
Components of Design
Components of blood turbulence monitor
1.) Pulsatile Blood pump
2.) Dacron Tubing
3.) Heated Water Bath
4.) Valve securing device
5.) Two actuated sample valves
6.) Semi permeable membrane
7.) Spectrophotometer
8.) PIC 16F877A, 40 pin microcontroller for data acquisition
9.) Labview Program for user interface and results display
System Overview
Pulsatile Blood Pump
Heated Water BathFlow Rate Indicator
Temperature Probe
Artificial Heart Valve
Pre-Heart Valve
Sample Port #1
Dacron Tubing
Post-Heart Valve
Sample Port #2
Input Stream
Return Flow
Semi Permeable
Membrane
Semi Permeable
Membrane
Dacron Tubing
Condensation polymer obtained from
ethylene glycol and terephthalic acid.
High tensile strength, high resistance to
stretching, both wet and dry, and good
resistance to degradation by chemical
bleaches and to abrasion.
Typically used in aortic grafts.
Minimal damage to red blood cells.
Sample Valves
Two actuated valves will be used to sample the blood before and after circulating through the heart valve
The sample valves used will be composed of 316L Stainless steel The contact surface of the valves will be electropolished to
prevent small blood clots from forming in crevices
The opening of the valves will be controlled using a microcontroller and user interface on Labview. The valves will automatically close after 30 seconds of being opened.
Sample Valves
The two sample valves will open when triggered by an input voltage
Using a 555 timer, a voltage pulse with duration time, T, will created. The output signal of this timer will be used to trigger the opening of the sample valves
In the circuit chosen, time duration T = 1.1*R*C
555 Timing Circuit
VCC
OUT
U1555_TIMER_RATED
GND
DIS
RST
THR
CON
TRI
VCC
12V
XSC1
Tektronix
1 2 3 4 T
G
PR110kΩ
R210kΩR3
100kΩ
C110uF
J1Key = Space
J2Key = Space
1
3
VCC
2
0
4
Probe2,Probe1
V: 0 V V(p-p): 0 V V(rms): 0 V V(dc): 0 V I: 0 A I(p-p): 0 A I(rms): 0 A I(dc): 0 A Freq.:
Temperature Control
To keep the system at a temperature of 37 degrees C to simulate the human body temperature, the Dacron tubing will be immersed in a heated water bath
A platinum RTD will be used to measure the temperature of the circulating blood inside tubing.
Output of RTD will be sent to microcontroller. If temperature drops below 37 degrees C, the PIC will send a
signal to water bath heater to turn on.
When temperature rises above 37 degrees C, the heater will be programmed to shut off.
Temperature Control Circuit
U1
8051
P1B0T21
P1B1T2EX2
P1B23
P1B34
P1B45
P1B5MOSI6
P1B6MISO7
P1B7SCK8
RST9
P3B0RXD10
P3B1TXD11
P3B4T014
P3B5T115
XTAL218
XTAL119
GND20
P2B0A821
P2B1A922
P2B2A1023
P2B3A1124
P2B4A1225
P2B5A1326
P2B6A1427
P2B7A1528
P0B7AD732
P0B6AD633
P0B5AD534
P0B4AD435
P0B3AD336
P0B2AD237
P0B1AD139
P0B0AD038
VCC40
P3B2INT012
P3B3INT113
P3B6WR16
P3B7RD17
PSEN29
ALEPROG30
EAVPP31
VCC
5V
VCC
U2
MAX232E
C1+C1-
C2+C2-
T1IN
T2IN
R1OUTR2OUT
GND
R2INR1IN
T2OUT
T1OUT
V+
V-VCC
VCC
5VVCC
1
2
C110uF
C210uF
34
5
6
C310uF
7
C410uF
8
C5
22pF
C6
22pF
0X1HC-49/U_5MHz
10
9
VCC
5VR1
1kΩ
VCCC7
100nF
J1
Key = A
0
11
HEATER
S1
HEATER
0R3
330Ω
12
13
X2RTD
XSC1
Tektronix
1 2 3 4 T
G
P
16
015
R21kΩ
R41kΩ
R51kΩ
V112 V
0
18
14
17
GND
GNDGND
GND 0
Spectrophotometer
Once sampled, the blood will pass through a semi permeable membrane to filter the blood cells from the blood plasma
A spectrophotometer will be used to measure the absorbency of light by the filtered blood plasma.
Blood turbulence will be calculated using the ratio of free hemoglobin found in the blood before and after circulating through the heart valve
Pulsatile Blood Pump
The flow of the working fluid will be
controlled using the Harvard Apparatus
Pulsatile Blood Pump for Large Animals;
Hemodynamic Studies Model # 553305.
Pulsatile Blood Pump
• Pulsatile output simulates the ventricular
action of the heart
• Minimal hemolysis due to material
choices and mechanisms.
• Ideal for moving emulsions, suspensions,
and non-Newtonian fluids such as blood.
Pulsatile Blood Pump
It features silicone rubber-covered heart-type ball valves and smooth flow paths which minimize hemolysis. The innert materials used silicone rubber, acrylic plastic, and Teflon are the only components contacting the fluid. The pumping head can easily be taken apart and reassembled for sterilization.
Pulsatile Blood Pump
Pump Mechanism
A positive piston actuator and ball valves
simulate the pulse action. Positive piston
action prevents changes in flow rates,
regardless of variations in resistance or back
pressure. The piston always travels to the end
of the ejection stroke, independent of the
volume pumped. The Pump completely
empties at each cycle, just like the heart.
Pulsatile Blood Pump
Specifications of the
#553305
The variability of the
stroke volume and
stroke rate allow for a
variable flow rate
between 150 to
10,000 mL/min
Specifications Model #553305
Accuracy 2%
Average Linear Force 25 lbs
Depth English 13.5 in
Depth Metric 337 mm
Display LED
Height English 20 in
Height Metric 500 mm
Minute Volume, Stroke Vol. x Rate Metric 150 to 10,000 ml
Net Weight English 32 lbs
Net Weight Metric 14.5 kg
Phasing Adjustable Phase
Pump Function Infusion Only
Rate, Stroke/Min. 10 to 100
Reproducibility 0.50%
Stroke Volume Range, Adjustable Metric 15 to 100 ml
Systole/Diastole Ratio
35% to 50% of total
cycle
Tube ID English 0.625 in
Tube ID Metric 15.9 mm
Voltage Range 115 VAC, 60 Hz
Width English 8.5 in
Width Metric 212 mm
Measuring Flow Rate FM51
Flow transmitter
FM30-S paddlewheel flow
sensor
Runs on batteries that can
easily be replaced when
necessary.
Will be added in-line with the
Dacron tubing to display the
flow rate.
Types of Common Artificial Heart
Valves
Caged Ball, mechanical
Tilting Disc, mechanical
Two Main Types: Mechanical and Bioprosthetic
Bileaflet, mechanical
Animal Valve, bioprosthetic
Heated Water-Bath
The heated water-bath assembly will be big
enough to encase both the input stream and
the return stream.
Dimensions: 6.5” x 4” x 3” (L x W x H)
Four, 1.02inch holes on the front and back,
ensure a good fit for the 1inch dacron tubing,
minimizing external vibrations due to a lose fit.
Heated Water-Bath: Schematic
Heated Water-Bath: Final Look
Membrane Holder
This design of the holder will allow the
user to lay the semi-permeable membrane
under the flow of the exiting flow.
The filtrate will pour in a funnel cone and
into a test tube, that will be set up in a
spectrophotometer, under the holder.
Membrane Holder
In-Line Valve Holder
This device is capable
of holding mechanical
heart valves in-line for
clotting factor
evaluation.
4 adjustable screws
to secure valve in
place.
Dacron
Tubing
Adjustable Pin
Main Chamber
Tubing to Chamber
Connector
Dacron
Tubing
IN
OUT
VALVE HOLDER ASSEMBLY
Sample Collection
Actuated Valve Opens at set intervals to collect
blood samples from the stream.
A sample before the heart valve, and a sample
downstream of the heart valve.
The blood is filtered using a semi-permeable
membrane to collect the blood plasma only.
Plasma-free hemoglobin levels determined by
spectrophotometer output to LabVIEW.
Fluid Dynamics
The Reynolds shear stress has been frequently used as equivalent to the viscous shear stress in numerical simulations aimed at estimating blood cell damage potential. An empirical equation based on the data obtained in Wurzinger et al. links the RBC damage to shear stress and exposure time was developed in Giersiepen et l.:
where the RBC damage index LRBC is measured as plasma free hemoglobin level, texp is exposure time (in seconds) and τ shear stress (N/m2).
“Characterization of Hemodynamic Forces Induced by Mechanical Heart
Valves: Reynolds vs. Viscous Stresses.” Annals of Biomedical
Engineering, Vol. 36, No. 2, February 2008 ( 2007) pp. 276–297
Determining Free Hemoglobin
Using Spectrophotometer and LabVIEW
Absorption coefficient values for
oxyhemoglobin (o), reduced
hemoglobin (r) and water.
Using absorbance to
measure Plasma Free
Hemoglobin
Plasma Free Hgb Level
Absorbance values from the
spectrophotometer are sent to LabVIEW
where the values are correlation with the
absorption coefficients.
Plasma Free Hemoglobin Levels are then
calculated and output to the user through
the use of a LabVIEW virtual instrument
(VI).
LabVIEW VI Block Diagram
Calculating Turbulence from
Hemolysis Rate
http://wiki.nus.edu.sg/display/Hemolysis/Behavior+of+Red+Blood+Cells
Rate of Hemolysis
τ= shear stress (N/m2)
Δt = exposure time (seconds)
Hemolysis Correlation for laminar steady flowAbsorbance
By relating the change in absorption as measured by the spectrophotometer,
the rate of hemolysis in the sample can be calculated. Once this is known
the shear stress can be calculated.
Turbulence ( )du
dy
-Add eddy viscosity (η) to turbulent flow shear stress equation.
-Turbulence exerts larger shear stress (τ) on adjacent fluids.
-Red Blood Cells can be damaged by shear stresses on the order of 1 to 10 N/m2, and platelet function can be altered by shear stresses on the order of 20 to 60 N/m2. Platelet damage seems to increase linearly with time of exposure to a constant level of shear stress, which indicates that shear-induced platelet damage is cumulative.
The turbulence will be calculated from the shear stress equation
using LabVIEW. This virtual instrument will display the turbulence
value on the screen as the closed-loop simulation is in progress.