Operator s Manual Development of a Pulsatile Left Heart Simulator

Transcription

1 0 Operator s Manual Development of a Pulsatile Left Heart Simulator Stephanie Bendtsen, Joseph Calderan, Celeste Dupont Team #17 Client #25 Client Contact: Dr. Wei Sun, University of Connecticut Tissue Mechanics Lab, 260 Glenbrook Road, Unit 2247, Storrs, CT 06269, (860)

2 1 Important Safety Instructions Handle electric components with care to avoid electric shock If wires become exposed, shut off system and cover them before using flow loop again When handling biological tissue valves, wear gloves and avoid contact with eyes, nose, mouth and open wounds Don t keep biological tissue valve in system for extended periods of time when not testing to avoid drying of the valve All biological tissue should be handled as detailed by the UConn Environmental Health and Safety Department Tighten the screws of the valve housing and bolts of the system securely to avoid leaks If the system leaks, shut off the air pump and seal with silicone before running the system again Use washers between the Plexiglas and aluminum to avoid cracking of the Plexiglas Turn off the air source when not in use Make sure to turn off the air source before disconnecting from the system

3 2 Parts and Accessories Figure 1. Atrium Chamber Figure 2. Mitral Valve Housing

4 3 Figure 3. Ventricular Chamber before compressing together Figure 4. Electromagnetic Flowmeter probe Figure 5. Square-Wave Electromagnetic Flowmeter Front Panel

5 4 Figure 6. Pulsatile Flowmeter Figure 7. Pressure Tap in the top of the Ventricular Chamber

6 5 Figure 8. Transbridge 4M Pressure Amplifier Figure 9. Lab-Trax-4/16 Data Acquisition (DAQ) Box Figure 10. Aortic Valve Housing

7 6 Figure 11. Aortic Valve Housing with mounted tissue valve Figure 12. Aortic Turn Component Figure 13. Compliance Chamber I - Dragon Skin 10 Platinum Cure Silicone Rubber

8 7 Figure 14. Compliance Chamber II - Layered Punch Balloons Figure 15. ViVitro Throttle Valve

9 8 Features Horizontal orientation of flow loop using a series of threaded rods running through the components allows for easy assembly of the system This layout also allows for integration of aortic roots into the system without fear of pressure curve variation due to raising the compliance chambers Components can be easily disassembled to adjust leaks or interchange various components Valves can be easily inserted and removed from the flow loop by tightening and loosening the set screws on the top and bottom of the valve housings Both the inlet and outlet sides of the mitral and aortic valves can be viewed and imaged Compliance chambers, pressure pumps and throttle valve can be adjusted to allow precise control of the pressure values and waveforms Pressure waveforms can be easily recorded and analyzed using analytical LabScribe2 software Cheaper than current ViVitro replacement heart valve testing system commercially available

10 9 Table of Contents Important Safety Instructions... 1 Parts and Accessories... 2 Features Introduction General Overview Instructions Maintenance Technical Description Mechanical Components Atrium Chamber Valve Housings Pulsatile Air Pump Ventricular Chamber Ascending Aorta Electrical Components Troubleshooting Troubleshooting the Square-Wave Electromagnetic Flowmeter Pressure Transducers Adjusting the pressure and flow curves Leaks... 38

11 10 1 Introduction 1.1 General Overview This pulsatile left heart simulator serves to test heart valve replacements previously benchmarked in Dr. Sun s lab and to ensure that they function properly. The pulsatile flow loop simulates and recreates the hemodynamic pressure and flow conditions that exist in the left side of the heart. The model includes windows on both sides of the ventricle so that images and videos can be taken of the mitral and aortic valves functioning during testing. These pictures and videos can then be studied and analyzed. The data obtained from this new system will give insight as to whether or not the replacement valves are functioning properly and can be implemented into human patients suffering from heart valve disease. The flow loop simulates blood flow from the left atrium all the way through to the ascending aorta. Along the way, the water passes through the mitral valve, the left ventricle, and the aortic valve. Upon completing travel through the ascending aorta the water must pass through a section that simulates the resistance of the body on blood flow before the blood returns to the heart. This is achieved through the use of compliance chambers and a throttle valve that retains a high pressure in the aortic region and outputs a low pressure returning to the atrium. After passing through this section the water returns to the left atrium so it can pass through the loop again. A flowmeter probe is located directly before the aortic valve chamber to measure the average flow rate of the water in the flow loop. It connects to a square-wave electromagnetic flowmeter which is connected to the computer. The flow rate of the system is recorded and analyzed using LabScribe2 analytical software. Pressure sensors are also connected to pressure taps on the top of the ventricle and aortic turn components. The left ventricular and aortic pressures are measured and waveforms are recorded using the LabScribe2 program. The waveforms can then be analyzed and adjusted if necessary by pressurizing the compliance chambers, or adjusting the settings on the pulsatile air pump or throttle valve. The horizontal orientation of the flow loop is the most advantageous aspect of the device. The implementation of four long screws running through the x and y planes of the ventricle chamber allows all other components to be attached and secured to the ventricle using the screws as well. The valves can easily be inserted and removed from the valve housings using small set screws that screw in and help hold the valve in place. The orientation of the ventricle also allows for images and videos of the inlet and outlet sides of both the mitral and aortic valves to be obtained. Markers may be placed on the tissue valve leaflets to measure the movement and displacement.

12 11 Figure 1.1: Assembly of flow loop 1.2 Instructions 1. Connect the square-wave electromagnetic flowmeter to the computer 2. Connect the Lab-Trax-4/16 DAQ box to the computer 3. Connect the Transbridge 4M to the LabTrax-4/16 DAQ box 4. Turn on the square-wave electromagnetic flowmeter and the Transbridge 4M to allow them to warm up. It takes approximately 5 to 10 minutes for the flowmeter to settle before accurate readings can be taken 5. Slide a long threaded rod vertically through the z-plane through each of the four holes located on the bottom portion of the ventricular chamber Figure 1.2: Orientation of Ventricular Chamber

13 12 6. Make sure the rubber ventricular sack is fit in its designated cut Figure 1.3: Ventricular Chamber before compressing together 7. Add washers and wing nuts to the underside of the ventricle, making sure they allow the ventricle to stand level 8. Slide the top portion of the ventricle on so it lies flat on the bottom portion 9. Add washers and wing nuts to the top of the ventricle Figure 1.4: Assembled Ventricular Chamber

14 Tighten both the top and bottom wing nuts 11. Slide a long threaded rod through each of the four holes in the y-plane of the top part of the ventricle 12. Insert the mechanical valve into the mitral valve housing and tighten the top and bottom set screws to secure it in place. A small silicone gasket can be placed under the screw head to prevent leaking. The front side of the mechanical valve faces inward so that the metallic leaflets open inwards towards the ventricle. Make sure the O-rings are placed in the appropriate cuts on each side of the valve housing. Figure 1.5: Open and closed configurations of Mechanical Mitral Valve Figure 1.6: Mounting Mitral Valve into Valve Housing 13. Slide the mitral valve housing onto the rods so that it is tight against the ventricle

15 14 Figure 1.7: Mounting Mitral Valve Housing onto Ventricular Chamber 14. Slide the bottom atrium component onto the rods so that it is tight against the mitral valve housing. The open topped chamber of the atrium is secured to the bottom portion through a PVC tube that is sealed with silicone. A PVC tube is silicone sealed to the opening at the left side of the bottom atrium component and is threaded to connect to a pipe threading attached to the pulsatile flowmeter Figure 1.8: Mounting Atrium Chamber onto Ventricular Chamber 15. Slide the Plexiglas mitral valve window and rubber gasket onto the rods so that it fits tight against the bottom atrium component

16 15 Figure 1.9: Mounting Window onto Atrium Chamber 16. Add washers and wing nuts against the window and the end of the ventricle and tighten evenly so the system is tight and secure in the y-plane 17. A wooden block should be inserted under the atrium to keep the flow loop level Figure 1.10: Window Mounted onto Atrium Chamber 18. Add a threaded rod to each of the four holes running through the top ventricle portion in the x-plane Figure 1.11: Inserting Threaded Rods into Ventricular Chamber

17 Slide the aortic valve housing onto the rods, leaving space for the flowmeter 20. Add nuts against the aortic valve housing 21. Insert the flowmeter probe between the ventricle and aortic valve housing a. The flowmeter must be properly grounded in order for accurate data to be collected. The most effective method found as this date was to take an aligator clip and attach it to both the mitral valve housing and the aortic valve housing. The grounding clip (attached to the flowmeter) was then attached to one end of the alligator clip. b. Additionally the flowmeter must be set to the proper settings in accordance with the flow probe being used at the time. For the aortic flow probe the system was calibrated to run at the following conditions i. Range (C Hi) ii. Frequency (100 Hz) iii. Probe (+) iv. Mean (Hi) v. Probe Factor (500) vi. Balance (500) c. If data from the flowmeter is erratic (abnormally high flow values) it is recommended that the probe is checked for damage and that recalibration of the system is performed using the instruction manual provided with the flowmeter 22. Tighten the nuts against the aortic valve housing, compressing the flowmeter to the ventricular chamber Figure 1.12: Compressing Aortic Valve Housing and Flowmeter to Ventricular Chamber

18 Use gloves to insert the biological tissue valve in to the aortic valve housing Figure 1.13: Mounting Aortic Valve into Valve Housing 24. Use a screw driver to tighten the top and bottom set screws of the aortic valve housing and make sure the valve is secure. Small silicone gaskets can be placed under the screw heads to prevent leaking 25. Place the thick rubber gasket in the O-ring cut on the aortic valve housing Figure 1.14: Adding O-ring and Gasket to Aortic Valve Housing

19 Slide the Plexiglas aortic turn component onto the rods so that it fits tight against the aortic valve housing. A PVC tube is sealed with silicone to connect the side opening of the aortic turn to a tube threading connected to compliance chamber II Figure 1.15: Adding Aortic Turn and Compliance Chamber II 27. A wooden block should be inserted under the compliance chamber and aortic turn to keep the flow loop level Figure 1.16: Wooden Blocks to Support Aortic Turn and Compliance Chamber II 28. Add compliance chamber I tight to the aortic turn so the the opening is in the center of the cylinder. The compartment with the shorter tube and stopcock attached should be against the aortic turn. The compartment with the longer tube and syringe attachment should be facing away from the loop.

20 19 Figure 1.17: Adding Compliance Chamber I 29. Slide the Plexiglas window onto the rods against the other end of the cylinder Figure 1.18: Securing Compliance Chamber I with window 30. Add washers and wing nuts against the window and ventricle on the opposite end 31. Tighten the nuts after the window at the end of compliance chamber I, making sure that each side is evenly tightened. When tightening the wing nuts, hold the wing nuts on the opposite side of the ventricular chamber so that the nuts in the middle do not become loose

21 20 Figure 1.19: Compliance Chamber I added to system 32. Check the nuts between the aortic valve and the aortic turn to make sure that they did not become loose. If they are loose, tighten them against the aortic valve housing with a wrench 33. Attach the tubing coming from the inlet side of the throttle valve to the hose barb coming from the balloon compliance chamber Figure 1.20 Attaching Throttle Valve to Compliance Chamber II 34. Attach the tubing from the other side of the throttle valve to the bottom hose barb of the pulsatile flowmeter

22 21 Figure 1.21: Attaching Throttle Valve to Pulsatile Flowmeter 35. Attach stopcocks to pressure tap tubing and stopcocks on the pressure taps installed in the top of the ventricle, aortic turn and both compliance chambers Figure 1.22: Stopcock attached to Ventricular Chamber

23 Attach the tube from the pulsatile air pump to the hose barb on the bottom part of the ventricular chamber Figure 1.23: Pulsatile Air Pump connection to Ventricular Chamber 37. Attach the tube for the air supply to the pump connection Figure 1.24: Attaching air supply to Pulsatile Air Pump

24 Connect the flowmeter probe to the square-wave electromagnetic flowmeter Figure 1.25: Connecting Electromagnetic Flowmeter Probe to Flowmeter 39. Attach the pressure sensors to their respective pressure taps on the top of the ventricle and aortic turn component Figure Connecting Pressure Sensor to stopcock

25 Turn the air source on Figure 1.27: Air supply knob 41. Add enough water to the system through the atrium so that the water level is about a quarter of the height of the chamber after the system fills with water 42. Open the stopcocks just enough for a small amount of water to come out to get rid of the air in the system 43. Open the knobs on the pressure sensors until water starts to come out to let out any air bubbles. 44. Turn the switch on the air pump to on to begin running the system 45. Open up the LabScribe2 program on the computer 46. Press Record to begin recording the flow rate, left ventricular pressure and aortic pressure and aortic flow of the system 47. Press Stop when the test is finished 48. Turn the switch on the air pump off 49. Turn off the air source and disconnect from pump if done testing. If not, turn the air back on before the next test

26 Once testing is complete, drain the water from the system by removing the tube connecting the balloon compliance chamber to the throttle valve and placing it in a bucket to collect the water 51. Loosen the screws at the end of the Plexiglas plate after the first compliance chamber and slide the aortic turn component and compliance chamber to the right to make space to remove the tissue valve 52. Using a screw driver, loosen the set screws on the top and bottom of the aortic valve housing 53. Using gloves, remove the tissue valve and put back in the glutaraldehyde container and into the refrigerator 2 Maintenance If any solution other than water is used in the flow loop, it is recommended that a full clean of each part is performed routinely to prevent damage to the system and clouding of the viewing windows o Additionally - if water is used, all of the fluid should be removed from the system after use. If the viewing windows become blurry or opaque through constant use is recommended that they be polished using a buffering wheel and an abrasive compound (these are present in the UConn machine shop) The pressure transducers should be checked each time they are connected to the system to ensure their accuracy. If the readings are off recalibration should occur. The compliance balloons may deteriorate over time and may need to be replaced The tissue valve fabricated for use in this system must be refrigerated in a glutaraldehyde solution to prevent the tissue from rotting Several places along the loop (where piping connects to the acrylic chambers especially) may become loose if the system is handled roughly. This could break the silicone seal around these components used to prevent leakage. If one of these seals breaks it should be replaced with clear waterproof silicone. Components that utilize threading to attach to one another may start to leak after repeatedly removing and reattaching to one another. If this is the case the threading should be coated with PTFE Thread Seal Tape. o If further leaks persist a silicone seal can also be added around the components

27 26 The Plexiglas is fragile and may develop cracking over time and repeated use. If this happen, replacement parts can be machined. o To prevent this, washers should be used whenever connecting parts via compression. This will distribute the forces more evenly and should reduce the risk of cracking one of the components. The flowmeter probe and the pressure transducers are delicate and should be handled with care. Routine checks should be made to ensure that they are still providing accurate readings. If they are not accurate, they should be re-calibrated. The compliance chambers may develop air leakage over time. If this is the case the chambers should be pressurized with air or water and the source of the leak should be found and sealed. If any metal components become corroded or rusted they should be promptly replaced. If wires become exposed, turn off the system and cover them 3 Technical Description 3.1 Mechanical Components Atrium Chamber The first component of the pulsatile flow loop is the atrium chamber. Water is supply to the flow loop through the atrium. The main purpose of the atrium chamber is to serve as a reservoir, holding excess water not currently used by the system. Figure 3.1 shows the atrium previously built by a graduate student of Dr. Sun s research team. The atrium design consists of a 5.75 by by 3.25 open topped chamber of Plexiglas. The large open-topped chamber allows for a fluctuation in volume without causing a drastic increase in pressure throughout the rest of the system. This is important because an increase in pressure occurring at the beginning of the loop would be experienced throughout the rest of the system. As a result, pressure readings obtained at the mitral and aortic valves would be inaccurate, as would the physiological waveforms of the system. A PVC tube connects the bottom of the atrium to a 5.25 by 3.5 by 3 block of Plexiglas. This component has a hole allowing the water to flow through to the mitral valve. The mitral valve chamber will be compression fit against the side of the output of the atrium which will prevent leaks around the valve. Four set screws run through the bottom atrium component, mitral valve chamber and ventricular chamber to pressurize the system. This will ensure pressurization and correct pressure waveforms to be produced by the mitral valve. A PVC tube is connected to the side of the bottom atrium chamber to allow the water traveling throughout the system to return to the atrium and flow through the system again.

28 27 Figure 3.1: SolidWorks Image of Atrium Chamber Valve Housings The designs of the mitral and aortic valve housings are the same, allowing for mechanical, bioprosthetic and biological tissue valves to be securely implemented into the flow loop. The mitral valve is a key aspect of this flow loop because it acts as a doorway for fluid to flow through to the ventricle so it can then be pumped throughout the system. The mitral valve is a one way valve. As fluid is pulled into the ventricle, the two valve leaflets open allowing fluid passage. When the ventricle contracts pushing fluid out, the pressure of the two leaflets pushes them backwards, closing off the path. The mitral valve used in this system is a mechanical valve available in Dr. Sun s laboratory. Valves are manufactured and sold to hospitals, making it very difficult and expensive to obtain new ones. One of the key goals of this project is to be able to incorporate different sizes and types of valves into the mitral and aortic positions. The design of the valve housing reflects this issue. The housing consists of a solid aluminum rectangle (5.25 x3 x0.5 ) with a hole bored into it with a diameter of 1. This hole extends through the majority of the rectangle (0.4 ) until the end where the diameter is smaller, allowing the valve to rest against a flat surface (Fig. 3.2). A biological tissue valve is inserted in the aortic valve position. This valve type consists of a sewing ring or annulus at the base that is supporting three struts. Between these supports are three tissue leaflets that meet in the middle. A crucial characteristic when attaching one of these valves is that the three struts must have a small amount of space to flex as the valve opens. To fix this valve in place, a thin-walled steel cylinder with an outer diameter the same as the diameter of the larger hole will slide down onto the valve once it has been placed in the chamber. The cylinder will be pushed down to compress the valve in place to prevent sliding. Along the rectangle four holes will be drilled from each edge face. Set-screws will be used to hold the cylinder in place, holding the valve steady in the process.

29 28 Figure 3.2: Valve Housing Pulsatile Air Pump The pulsatile air pump is capable of producing adjustable systolic and diastolic pressures. The pump alternates between two phases (systole and diastole). The systolic phase is adjustable using the top dial control (Fig. 3.3) and acts to push air into the ventricle, simulating the contraction of the heart. The diastolic phase is controlled by the bottom dial and does the opposite. Air is pulled into the pump out of the ventricle to simulate the relaxing of the heart. The other controls included on the pump are systolic duration, which has been kept at 350 ms, and the heart rate in beats per minute. The power switch as also on this front panel on the bottom left. The pump should be supplied with filtered air or CO₂ above 25 psi and below 85 psi. Electrical connections are VAC and 60 Hz. Figure 3.3: Pulsatile Air Pump

30 Ventricular Chamber The ventricle pumps fluid through the system powered by the pulsatile air pump described in Section The ventricle design consists of a latex sack housed in an airtight chamber. The pulsatile air pump is connected to the bottom of the chamber. As seen in Fig. 3.4, the ventricle chamber is designed as a square, with the flow entering then leaving in a right angle. The top portion of the ventricular chamber is a 5.25 x 5.25 x 3 block with a 3 diameter cavity in the center. This square design allows for visualization of the mitral and aortic valves while the system is running. Cameras can be mounted on two of the sides of the ventricle which will allow visualization of both valves simultaneously without affecting the overall physiological flow waveforms. The two paths of view cross along the center of the ventricle and continue through the valve chambers until they reach view windows at either the exit from the atrium, or the entrance to the compliance chambers. Both windows are detachable but the window following the aortic valve must be removed to attach the first compliance chamber and obtain more accurate waveforms. To implement the systolic phase into the flow loop, the pump pushes air through a tube into the airtight chamber housing the latex sack, directly influencing the internal pressure. As a result, the sack collapses inward, pushing fluid through the aortic valve. Simultaneously, this contraction of the ventricle applies pressure to the mitral valve which will close it, preventing water from entering the atrium via this route. In contrast, the diastolic phase of the heartbeat is when the ventricle relaxes and fluid flows through the mitral valve to refill the ventricle. To simulate the diastolic phase, the pump draws air from the ventricular chamber, creating a vacuum. As a result, the sack inflates to its original size and is filled with fluid from the atrium through the one way mitral valve. This process accurately simulates the muscle contraction and relaxation periods of the human heart, enabling the valve function to be focused on during testing. Figure 3.4: SolidWorks Model of Ventricular Chamber

31 Ascending Aorta The ascending aorta is comprised of the aortic turn, compliance chambers, throttle valve and tubing. Since the Plexiglas and tubing are very stiff, the compliance chambers allow the water to expand against the walls of the loop during heart beats. This softens the pressure waveforms as well Aortic Turn The aortic turn is the first component simulating the branching of the blood from the aortic valve out to the rest of the body. It is a 5.25 by 3.25 by 3 block of Plexiglas with two holes of 1 diameter; one running straight through it to compliance chamber I and one off at a right angle to compliance chamber II Compliance Chamber I The outer tube of this chamber is approximately five inches in length and has an inner diameter of three inches and an outer diameter of three and a half inches. The chamber was cut in half and a sheet of Dragon Skin 10 Platinum Cure Silicone Rubber was placed in between the two pieces (Fig. 3.5). To make attaching the chamber onto the rest of the device easier, the two halves were glued to the silicone sheet, creating one piece. Gasket material was also glued to either end of the chamber to prevent leaking when assembled. An end plate compresses the chamber to the block after the aortic valve using threaded rods, washers, and wing nuts. The first compartment, closest to the aortic valve, fills with water and air is let out of the system through the pressure tap on the top. The second compartment is air-tight so that a syringe or other hand pump, attached to the pressure tap, can pressurize the compartment and control the amount of compliance. Drawing air out of the second compartment allows the membrane to expand more and pushing air in limits the extent of expansion. These properties can soften or spike the waveforms depending on the extent of each action. Figure 3.5: Compliance Chamber I

32 Compliance Chamber II The outer tube of this chamber is approximately eight inches in length and has an inner diameter of three inches and an outer diameter of three and a half inches. The tube within the chamber is made up of three layered commercial punch balloons with the ends cut off. As seen in Fig. 3.6, the balloons are connected to hose barbs using hose clamps and the hose barbs connect to the rest of the system. The fluid flows through the rubber compartment within the tube so that the pressure can adequately impact the flow. The chamber is air-tight and connected to a controllable pressure pump gauge through the pressure tap so that as the pressure within the tube is changed, the size of the inner balloon changes accordingly. Increasing the pressure in the chamber decreases the size of the balloons and increases the aortic pressure. This shifts the range of the waveforms up to higher pressure values. Figure 3.6. Compliance Chamber II Throttle Valve and Tubing The throttle valve acts to regulate the overall flow throughout the system. It has a numbered dial (from 0 to 5) that indicates how open the valve is. The dial allows the throttle valve to be easily adjusted and also to reproduce settings. This acts to retain a higher pressure system in the aortic section and a lower pressure system in the atrium. Increasing the number on the dial increases the overall flow of the system and decreases the aortic pressure whereas reducing the number on the dial decreases the flow and increases the aortic pressure. The throttle valve was taken from the ViVitro flow loop and implemented into this system after other valves were tested and found to be unsatisfactory. Tubing allows water to enter the throttle valve from compliance chamber II, leave the valve, and flow to the pulsatile flowmeter.

33 32 Figure 3.7: Throttle Valve Pulsatile Flowmeter The pulsatile flowmeter is implemented in the flow loop right before the water returns to the bottom atrium component. The flowmeter includes a metal piece that moves up and down the scale as the flow changes. The reading should be taken, not from the top of the metal piece, but from the widest part of it. An average of the highest reading and lowest reading gives an approximation for the average flow rate throughout the system. The purpose of including this flowmeter while still using the electromagnetic flowmeter was to have two methods of reading the flow rate and also to have a more immediate method of obtaining this reading. The flowmeter must be installed so that it is upright and no stress is put on the body of the meter. The flow should enter the flowmeter from the bottom and exit from the top. The maximum pressure that the flowmeter can withstand is 125 psi at 70 C and the temperature range is 33 F to 130 F. 3.2 Electrical Components A flowmeter probe, connected to the square-wave electromagnetic flowmeter, is mounted before the aortic valve housing to detect the flow rate and monitor regurgitation. The Electromagnetic Flowmeter has the following specifications as detailed in the operation manual provided with the device: Flow Range: 5ml/min to L/min Probe Excitation: 500Hz square-wave. 0.5 Ampere +/- 2%. Limited to +/- 15V with open circuit Probe Leakage Protection: Probe current is removed if more than 200 microamperes leakage to ground occurs. Amplifier Input: Differential 20 megohms plus 300pf. Maximum input voltage 2V peak to peak

34 33 Outputs: Simultaneous mean and pulsatile single-ended analog outputs capable of +/- 5V swing. Normal full scale mean output Output Impedance - 75 ohms protected against short circuit of infinite duration. Minimum load impedance for rated calibration accuracy, 1K ohms Calibration Signal: Toggle switch provides 1V +/- 5mV or 0.1V +/- 2mV on mean and pulsatile outputs to calibrate signals sent to computer Frequency Response: DC-100Hz +/- 3dB Linearity: +/- 1% Calibration Accuracy: +/- 5% DC Drift: (After warm up) +/- 5 mv Operating Temperature Range: degrees Celsius Power Requirements: 115V, +/- 10V 50/60 Hz, 25 watts, 3-wire grounding type plug The Waldhausen Design Pneumatic Blood Pump has the following power requirements: Electrical Connections o VAC o 60 Hz Gas Connections o Filtered air or CO2 only o 25 psi minimum, 85 psi maximum The front of the device should not be elevated more than 20 degrees higher than the back of the device Ambient temperature should not exceed 40 degrees Celsius 4 Troubleshooting 4.1 Troubleshooting the Square-Wave Electromagnetic Flowmeter The flowmeter came with a comprehensive booklet where it describes the device in great detail. This section contains a paraphrased list of what to do in terms of calibration and operation of the flowmeter

35 34 Figure 4.1: Front Panel of Electromagnetic Flowmeter (top and bottom) These steps should be followed when setting up a new probe or if the current probe is not reading accurately 1. Turn POWER and PROBE switches to OFF 2. Plug power cord in 3. Connect the flowmeter to the DAQ box (same box as is connected to the pressure transducers) 4. Turn the POWER switch on a. This should turn on the READY light and the ALARM light in the top right hand corner b. Depress the ALARM light so that it is no longer lit up 5. Wait 5 to 10 minutes for the device to stabilize 6. Set the PULSATILE Hz RESPONSE control to 10 and the MEAN switch to HI 7. Set the display meter to zero using the ZERO control nob on the front panel a. Here you should make sure that there is a coresponding zero voltage readout on the program you choose to use. In this case we used Labtraqs. b. Check to see that the 1 VOLT and 0.1 VOLT lever reads accurately on the program as well 8. The BALANCE control should be set at The PROBE FACTOR control should also be set to Connect a flow probe to the flowmeter

36 Test the probe by placing it in a non metalic beaker of water or saline a. Completely cover the probe with the solution b. Connect the grounding cable to a steel ring of wire and place it at the bottom of the beaker 12. Turn the PROBE switch to NULL. Adjust the NULL control until the lowest possible reading is shown on the flowmeter (this may not be zero) 13. Turn the PROBE switch to BAL and adjust the meter to zero using the BALANCE control 14. Turn the PROBE switch to + a. The meter should indicate zero. If it does not, adjust the BALANCE control until it does 15. Move the probe around in the fluid to check that the meter is recognizing the motion 16. Turn PROBE switch to OFF 17. Put the probe into the flow loop and turn the PROBE switch back to + Grounding can be a huge issue when it comes to collecting accurate results. The flowmeter and the probe are very sensitive to electrical interference around them and proper grounding is essential to recording accurate data. We found that the most effective way to ground this system was to connect the grounding wire to both of the aluminum valve housing sections. This was accomplished by connecting an alligator clip between the two valve housing components then connecting the grounding cable to one of the alligator clip leads. *The flowmeter probe was found to give an abnormally high voltage output when compressed. Be careful not to over compress the probe. **To check that the flowmeter is running properly the average aortic flow can be compared with the overall flow of the system by recording the maximum and minimum flow on the pulsatile flowmeter then averaging the two. 4.2 Pressure Transducers If the pressure sensors need to be re-calibrated follow these steps: 1. Make sure the pressure transducer is properly attached to the computer and DAQ box as described in the operation steps 2. Turn on the LabScribe2 program

37 36 3. Attach the pressure transducer to a hand pump with a pressure gauge on it Figure 4.2. Pressure Sensor attached to hand pump 4. Pump air into the transducer and record the both the pressure input and the corresponding voltage reading in the LabScribe2 program 5. In Excel create a graph comparing the pressure to the voltage reading 6. Create a line of best fit using this data 7. Using the line of best fit create a new window in the LabScribe2 program that correctly adjusts the voltage into mmhg (or whatever pressure reading it is calibrated as) ** It is also important to note that the pressure transducers should be opened and have a stream of water pass through them to remove any air bubbles from the tubing leading to the transducer. The air bubbles will alter the pressure curves and give inaccurate readings. This is due to the fact that air is compressible and water is not. To keep the data readings consistent with one another all air should be removed from the system as it would be highly difficult to get the exact same amount of air in each pressure line for each new test, 4.3 Adjusting the pressure and flow curves How each component adjusts each waveform. One of the major components that adjusts the pressure and flow curves is the pneumatic pump. The Waldhausen Design Pneumatic Blood Pump employs a two cycle pump that alternates between a low pressure tank and a high pressure reservoir tank that act in turn to produce a systolic and diastolic phase. The systolic phase corresponds to the time and pressure available to empty a blood pump (pushing air into the ventricle) and the diastolic phase corresponds to the time and pressure available to fill the blood pump (pull air out of the

38 37 ventricle). The systolic and diastolic pressures can both be adjusted by rotating the corresponding wheels. The other user controls on this device are the beats per minute and the systolic duration. The beats per minute determine the amount of cycles per minute - 60 beats per minute means 60 systolic phases and 60 diastolic phases. The systolic duration (adjusted in ms) determines the amount of time per beat that the systolic phase lasts. For example if the systolic duration is 300ms the diastolic phase will last 700ms when the pump is running at 60 beats per minute. If the systolic duration is kept constant and the beats per minute are changes the diastolic phase will increase or decrease proportionally. Increasing the systolic pressure both increases the overall pressure of the system and increases the flow rate. It will increase both the LVP and AP Decreasing the systolic pressure will decrease the LVP, AP, and aortic flow Increasing and decreasing the diastolic pressure will change the amount of fluid getting pumped through the system per beat. It should be run in the negative range as it is used to draw water into the ventricle by expanding the size of the ventricular sack. The more negative the pressure is the more fluid will be drawn into the system per beat. Increasing the beats per minute will increase the overall flow rate Increasing the systolic duration will change horizontal size of the LVP and AP. The peaks of the curves will last as long as the systolic duration. Another key contributor to changing the pressure and flow waveforms is the pressure reducing throttle valve that is connected between the balloon compliance and the atrium chamber. This acts to retain a higher pressure system in the aortic section (after the aortic valve and before the throttle valve) and a low pressure system in the atrium which is open to the air. It also acts to reduce or increase the total flow to the system. The throttle valve is changed by twisting the larger section. It is calibrated so that the there is a scale (from 0 to 5) that shows you what position the valve is open to. Opening the valve more (increasing the number on the dial) increases the overall flow of the system and decreases the AP Closing the valve (decreasing the number on the dial) increases the AP but reduces the flow throughout the system Decreasing the opening of the valve also acts to raise the minimum aortic pressure The other two things that can affect the flow curves are the balloon compliance section and the silicone compliance chamber

39 38 Increasing the pressure in the balloon compliance will increase the aortic pressure Altering the back pressure in either one of these sections will change the shape of the pressure curves. It will soften the curves or add spikes accordingly. All of these components must be used in sync with one another as they all change the system in similar ways. If one needs to increase the flow to the system while maintaining the same average aortic pressure they would need to open the throttle valve and increase the systolic pressure together. Relationships like these are learned through practice and use as each valve input into the system will require different settings to achieve the same hemodynamic conditions. 4.4 Leaks Leakage may occur in various parts of the system due to wear and tear and constant use. The following is a list of the parts with a high risk of leaking either air or water and the ways to correct this. Water leaks may occur at the connection points between the balloon compliance chamber and the turn after aortic chamber. The piping connecting the two is set in place through compression then sealed with silicone. If it starts to leak it is recommended that the piece is pushed back into place and a new layer of silicon sealant is applied. Water leaks may also occur at places where two threaded components connect to one another. To stop this leak Teflon tape can be applied to the threaded sections before they are reconnected. Silicone sealant can then be applied around the outside connection area completing the seal. Air may begin to leak out of the balloon compliance chamber. This may become noticeable when the balloon chamber starts to depressurize and the balloon increases in size (without any other alterations to the pressure and flow conditions). This may be hard to correct as the leakage location may be difficult to pin point. To assist in finding it the chamber can be detached, submerged in water and then pressurized. Any zones that leak air should be easily noticeable under water. Any other leakage may just be due to improper tightening of the system during assembly. Making sure the threaded rods are tightened evenly and tight enough can fix most of the leaks that the system encounters.