The overall goal of the following experiment is to demonstrate how a commercially available in vitro pulse duplicator can accommodate emerging tri leaflet, polymer heart valve prosthetics, and to evaluate the hydrodynamic metrics of the assembly. This is achieved by assembling a tube and valve holder to accommodate a tri leaflet valve configuration in the pulse duplicator As a second step, polymer valves are sutured in place and tested to measure their hydrodynamic metrics. Native porcine valves and mechanical heart valves are also tested to validate system hardware modifications to the mechanical design of the synthetic valve.
The results show that the modified pulse duplicator system can be utilized to evaluate polymer valves with native porcine and mechanical valve hydrodynamics, thus providing insights on the functional aspects of polymer valve design. Generally, individuals new to this method will get confused because the techniques are tedious and there are a lot of concepts related to hydrodynamic metrics that are necessary for thorough valve prosthesis evaluation and which are not typically taught in a traditional engineering curriculum. The implications of this technique extends towards the functional development of emerging heart valve prosthesis technologies because hydrodynamic assessment provides with insights on how to further improve the design characteristics of the prosthetic har valve, Along with Manuel.
Assisting him. In this demonstration will be Carl Lande bro and undergraduate student in my laboratory. This protocol begins with the fabrication of the assembly.
This includes a valve holder used to suture in the valve leaflets, a tube used to house the valve holder and surrounding accessories that secure the assembly onto the pulse duplicator system. A commercially available pulse duplicator system is also required Before the system is used first, prime the entire loop. Clean the loop system using soap and water.
During this process, replace any degraded tubes. Next, calibrate the instruments connected to the loop, which are the pump, the flow probe, and the pressure transducers. The calibration begins with a 1%saline solution, followed by a blood analog glycerin solution.
Typically calibrate these for making measurements at atrial, aortic and ventricular locations. Once calibrated, proceed with preparing the valves. Obtain four fresh pig hearts with the aorta intact from A-U-S-D-A approved slaughterhouse.
Unpack and rinse a heart with deionized water and place it in a receptacle filled with 1%antimycotic antibiotic in PBS on ice. Transport it to the hydrodynamic testing laboratory. Place one of the hearts in a dissecting pan and carefully remove its pericardium.
Looking at the ventral side, inspect the four chambers and locate the aortic arch on the intact aorta. Then separate the heart into halves. Cut horizontally three fourths of an inch below the annulus at the junction between the aorta and the left ventricle, and isolate the intact aorta attached to the left ventricular tissue segment.
Examine the aortic valve located in the aortic root for damage or calcification. This is the region between the ascending aorta and the lower annulus. If it looks good, split the aorta about an inch above the annulus, otherwise discard the tissue.
Then separate the left ventricular tissue segment below the annulus to isolate the aortic valve with the valve isolated. Proceed with the suturing to secure a valve to the holder. First, place it inside the valve holder.
Align the base of the valve with the base of the post holder. Then temporarily secure the valve with a paperclip. Be careful not to damage the commissure or the cusps.
Now, place sutures at the bottom of the valve holder. Feed the needle through the first hole and down to the bottom. Then in a looping fashion, suture the valve to the valve holder along the posts.
Continue suturing along the circumference of the holder. Finish the suturing with an additional suture around the tips of the posts for added security. Once sutures, secure the valve to all the posts.
Remove the paperclip in this demonstration. A vi vitro pulse duplicator system is used. The steps will be different with other systems.
Begin the evaluation by setting the heart rate of the system to 70 beats per minute. Next, select a flow waveform to drive the pump, which in this case is the S 35 waveform. Now switch on the amplifier and piston pump and allow them to warm up for 15 minutes.
When testing a bi leaflet valve, position it into the system in the aortic position for a sutured valve. First, position it inside the glass tube for the custom made assembly by sandwiching the tube with the top and bottom pieces and secure them with lateral screws. We have just inserted the polymer valve.
This is the same procedure we use to insert the native valve. Then position the assembly between the aortic chamber and the original aortic valve holder with the valve in position, smear vacuum grease on all of the junctions that could leak. Next, add two liters of 35%glycerin in saline to the atrial compartment.
Now that the system is filled, the most important step is to make sure that all components are well calibrated. Two people work together to set up the system. Now, make sure that the flow transducer is set for aorta position and turn it on using the instructions under the calibrate tab in the software, calibrate the pump and then the flow transducer and then the pressure transducers.
Once the calibrations are complete, start the pump at a low RPM until the fluid fills the aortic compartment. Check for leaks and seal them with additional vacuum grease. Turn the two stopcocks to the open position.
They are the aortic and ventricular transducers. Increase the RPM of the pump until the stroke volume reaches 80 milliliters per beat. Permit the system to run for 10 minutes until flow has stabilized.
This can be verified by observing the flow and pressure wave forms on the screen. When variation between the cycles is unobserved or very minor, the system has stabilized. Now in the VI test software, select the acquire mode and click on collect 10 cycles from the analyze mode, click on table and save the file.
Also, save an image of the waveforms using the photo snap. Option five, polymer four native porcine and two bi leaflet valves were compared. Flow rate was measured using an electromagnetic flow meter connected to a noninvasive flow probe placed at the interface location of the ventricle and aortic chambers.
Ventricular pressure was measured in the ventricle chamber using a micro tip pressure transducer superimposed on this. Result are reported values for native and B leaflet valves with a 29 millimeter diameter. From the literature.
Aortic pressure was measured just downstream from the aortic valve position using a micro tip pressure transducer. Again, previously reported values for 29 millimeter diameter valves are also given. In summary, many parameters were computed from the flow and pressure measurements made.
The size of the tested valves averaged around 22 millimeters in diameter by leaflet. Valves were difficult to obtain. Hence, their sample size is small.
Once mastered this technique, including sample preparation and hydrodynamic evaluation can be performed in about two and a half hours. We were able to demonstrate using a custom assembly that we built a way in which we can accommodate tri leaflet valve or tri leaflet polymer valve structures, and then subsequently incorporate these types of valves or these polymer valves into an existing commercial pulsatile loop for functional hydrodynamic evaluation. At the same time, we were able to demonstrate that we can compare these valves objectively to a native valve, which is also tri leaflet in geometry.
In our case, we use porcine native aortic valves because these valves are very similar to human valves. Finally, following these procedures, we can also look at other research areas such as the development of scaffold assembled valves that can be used for tissue engineering, heart valve purposes.
