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.