Artificial Heart Valve Turbulence Measurement Device

Transcription

1 Artificial Heart Valve Turbulence Measurement Device Team #7 Sarmad Ahmad Hillary Doucette Stephen Kustra

2 Background

3 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

4 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.

5 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.

6 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

7 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

8 System Overview Temperature Probe Dacron Tubing Return Flow Pulsatile Blood Pump Flow Rate Indicator Heated Water Bath Semi Permeable Membrane Post-Heart Valve Sample Port #2 Input Stream Artificial Heart Valve Semi Permeable Membrane Pre-Heart Valve Sample Port #1

9 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.

10 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.

11 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

12 555 Timing Circuit VCC XSC1 VCC 12V Tektronix R1 10kΩ R3 100kΩ R2 10kΩ U1 555_TIMER_RATED P G T 3 2 J1 Key = Space 1 J2 Key = Space RST DIS THR TRI CON VCC GND OUT 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.: 4 C1 10uF 0

13 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.

14 Temperature Control Circuit 0 C nF J1 Key = A C5 22pF C6 22pF R1 1kΩ VCC VCC X1 HC-49/U_5MHz 5V VCC 5V P1B0T2 P1B1T2EX P1B2 P1B3 P1B4 P1B5MOSI P1B6MISO P1B7SCK RST P3B0RXD P3B1TXD P3B2INT0 P3B3INT1 P3B4T0 P3B5T1 P3B6WR P3B7RD XTAL2 XTAL1 GND GND VCC U R4 1kΩ R5 1kΩ VCC 40 P0B0AD0 P0B1AD P0B2AD2 37 P0B3AD3 36 P0B4AD4 P0B5AD P0B6AD6 P0B7AD EAVPP 31 ALEPROG 30 PSEN 29 P2B7A15 28 P2B6A14 P2B5A P2B4A12 P2B3A P2B2A10 23 P2B1A9 22 P2B0A8 21 R2 1kΩ 0 X2 RTD C1 10uF C2 10uF 5 C1+ C1- C2+ C2- T1IN T2IN R1OUT R2OUT GND V1 12 V VCC 5V VCC VCC GND GND V- V+ T1OUT T2OUT R1IN R2IN 0 Tektronix C4 10uF U2 8 7 MAX232E 0 XSC1 P G C3 10uF T 1516 GND R3 330Ω 13 S1 HEATER HEATER 0

15 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

16 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 #

17 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.

18 Pulsatile Blood Pump It features silicone rubber-covered hearttype 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.

19 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.

20 Pulsatile Blood Pump Specifications Model # Accuracy 2% Specifications of the # The variability of the stroke volume and stroke rate allow for a variable flow rate between 150 to 10,000 ml/min Average Linear Force Depth English Depth Metric Display Height English Height Metric Minute Volume, Stroke Vol. x Rate Metric Net Weight English Net Weight Metric Phasing Pump Function 25 lbs 13.5 in 337 mm LED 20 in 500 mm 150 to 10,000 ml 32 lbs 14.5 kg Adjustable Phase Infusion Only Rate, Stroke/Min. 10 to 100 Reproducibility 0.50% Stroke Volume Range, Adjustable Metric Systole/Diastole Ratio Tube ID English Tube ID Metric Voltage Range Width English Width Metric 15 to 100 ml 35% to 50% of total cycle in 15.9 mm 115 VAC, 60 Hz 8.5 in 212 mm

21 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.

22 Types of Common Artificial Heart Valves Two Main Types: Mechanical and Bioprosthetic Caged Ball, mechanical Tilting Disc, mechanical Animal Valve, bioprosthetic Bileaflet, mechanical

23 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.

24 Heated Water-Bath: Schematic

25 Heated Water-Bath: Final Look

26 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.

27 Membrane Holder

28 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.

29 VALVE HOLDER ASSEMBLY Adjustable Pin IN Main Chamber OUT Dacron Tubing Tubing to Chamber Connector Dacron Tubing

30 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.

31 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, t exp is exposure time (in seconds) and τ shear stress (N/m 2 ). 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

32 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

33 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).

34 LabVIEW VI Block Diagram

35 Calculating Turbulence from Hemolysis Rate Rate of Hemolysis τ= shear stress (N/m 2 ) Δt = exposure time (seconds) Hemolysis Correlation for laminar steady flow Absorbance 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.

36 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/m 2, and platelet function can be altered by shear stresses on the order of 20 to 60 N/m 2. 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.