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Interview: Dr. Lyes Kadem discusses cardiovascular flows and the design of medical devices

August 30th, 2020

Dr. Lyes KADEM

Dr. Lyes KADEM

Lyes Kadem PhD, ing, is a Full Professor in the Department of Mechanical, Industrial and Aerospace Engineering Concordia University and Concordia University Research Chair for Cardiovascular Engineering and Medical Devices. Rob Fraser, ViVitro Labs Applications Manager, recently spoke with Dr. Kadem about his work in Laboratory of Cardiovascular Fluid Dynamics.

Rob Fraser Please tell us about your current work and projects you would like to highlight.

Dr. Kadem In the lab, we are working on two different areas. One is the fundamental understanding of cardiovascular flows and the second is the design and testing of medical devices.

When you understand the flow from a fundamental point of view, you can predict the appearance of any pathology and you know exactly what the medical device is supposed to do. Basically, you understand the ideal case scenario. For example, we perform studies to try to understand the fluid dynamics in the left ventricle when you have aortic regurgitation. This is quite an interesting flow. Instead of having the in flow only from the mitral valve, you have it also from the aortic valve.  From a fluid mechanic’s point of view, you have two pulse jets competing. For example, under certain conditions can you achieve a vortex reversal? We are also working on a project on mitral regurgitation and how it impacts the left atrium.

Other projects are related to Abdominal Aortic Aneurysm (AAA). We designed a setup where we simulate different severities and shapes of aneurysms of the abdominal aorta. We perform velocity measurements in order to develop new clinical parameters and eventually new medical devices. We also investigated the impact of the Tetralogy of Fallot on the right ventricle and specifically when there is a regurgitation through the pulmonary valve. For this, we designed a simulator dedicated to the right ventricle.

These are the most important current projects from a fundamental point of view. We have other projects to understand the impact of sudden deceleration on the cardiovascular system. We designed a small dummy of the aorta that goes along the lab and hits a shock absorber. What we are trying to do here is to gain a better fundamental understanding of the flow under such critical conditions.

Rob Fraser Is this like a car crash test dummy, except instead of putting on accelerometers, you’re actually looking deeper into what happens with the actual flows in the body, like during a car accident?

Dr. Lyes KADEM

Dr. Lyes KADEM

Dr. Kadem Correct. We designed an elastic aorta in a box with an aortic valve and a pulsatile flow with correct pressure wave forms. We try to see how the flow behaves during the acceleration and after the impact. This is important since the impact can lead to a tearing of the aorta  with 88% of cases in the isthmus. To give a basic example, if you take a flow which is in equilibrium, and then you kick it … let’s say I give you a pipe, you kick the pipe and the pipe receives energy. How would the flow in the pipe dissipates this energy? What are the flow structures that will build up to dissipate this energy? Typically, we’ll have secondary flow. This is was is interesting from a mechanical point of view.

The other aspect is the design of medical devices. We are trying to come up with ideas for medical devices – a left ventricle assist device and better control of the flow in a AAA. The other big project is trying to design a 3-D printed patient clone. The concept is that you get CT scan images of a patient. We 3-D print the heart cavities and then we make them beat. The idea here is to design a system for training doctors and testing medical devices under more realistic conditions. It includes a 3-D printed complete heart and all the major arteries. With the heart valves in the system, we can simulate different pathologies or we can implant new medical devices. We designed it in such a way to be MRI compatible and sent it to the University of Calgary, where I’m working with my colleague Dr. Julio Garcia to image the flow inside our 3-D model using 4D-MRI. The main concept is to create a portfolio of cases so that any medical device can be tested under more realistic conditions.

Rob Fraser Is this like a passive heart? Are the ventricles contracting? Or are you passing flow through a sort of a static model?

Dr. Kadem Actually, it’s active, so we can reproduce the pulsatile flow and this not trivial.  Well, we are competing against evolution so it’s not that easy. The classical approach like in the ViVitro system, or in a system that we designed in the lab, is that you always have an activation box. But in this case, to active the heart, we cannot do this so we used different techniques. One is using linear motors and pushers. So we had a linear motor actually pushing and pulling the 3-D printed ventricles. We figured out that it’s not optimal. OK, it works, but we are not quite happy with this. We are exploring now other approaches. One is based on soft robots. Do you know what a soft robot is?

Rob Fraser Not really, no.

Dr. Kadem A soft robot is something quite simple. If you are given an elastic tube and you put pressure inside, it will mostly inflate. But if you constrain the radial deformation, it will change its length significantly. So what we did is to take a model of a heart and wrap the soft robot around it to activate it with a cyclic deformation of the soft robot. We are also trying Origami robots. So those are like folds that you put in a bag. Let’s say you have a zigzag, you put it in a bag. And then when you put air pressure in, it will expand. And when you take out air it will contract. So it magnified the size of fibers. This is what we are exploring.

Rob Fraser All three projects – an LVAD, a better AAA and then the 3-D printed heart – those alone are massive projects. How are you managing all these projects with COVID? People can’t go into the lab, I assume? Are they working from home? Or what’s the situation?

Dr. Kadem  At first we had to stop. So we stopped for six to eight weeks. Actually all the labs were closed. And then I had to go back to the lab because we started a collaboration with Montreal Children’s Hospital regarding a COVID related project. We had Health and Safety figure out the maximum number of people who can work in the labs, Now they are starting with priority given to graduate students who are doing experiments. In the lab, the maximum I can have is four research assistants. I had to give priorities. It’s not totally obvious. And it depends on several things, for example, I have one Ph.D. candidate who is working on the effect of mitral regurgitation on the flow in the left atrium. He’s completely independent. He goes to the Lab, he does his experiments with the simulator and so on. But I also have summer students. They need more help and training and this is a bit more difficult to handle with COVID-19.

Rob Fraser What are your plans for the future?

Dr. Kadem The plan is that we’ll continue exploring the flow dynamics to better understand them. And we are patenting some ideas regarding the ventricle assist device.

Regarding the simulators, it is to make them more realistic. The activation process is really complex. The other more complex thing is to make them easily adjustable to reproduce realistic waveforms. It’s not trivial. Maybe this is something where artificial intelligence can be useful. Basically the concept is that you try different positions for your compliance, resistance and other parameters. And then you just have to enter the desired stroke volume, pressure, etc., and the system will  reproduce it directly.  There’s something interesting in that, like when I used the ViVitro system for the first time.

I was impressed by how easy actually it was to make the ViVitro system work. I put two students to work with the ViVitro. The project was on transcatheter valves and the evaluation of the bending stress depending on how much valve over-sizing you have. It was their first experience doing actual experiments. In a week or so they were mastering this. We learned a lot from this, and then we said, “Well, maybe we should design simulators that are really user friendly. The next step for this simulator, this manikin, is to make it more user friendly. When I try to picture this, I will be happy when we will reach the point where  I will be putting electrodes on myself, and while simulating exercise, the 3D replica of my heart will reproduce my actual conditions. I think if we manage to achieve this, I will be quite happy!

Rob Fraser How close do you think you are to that, to where you could have electrodes on your chest to a pumping model beside you? Is that five years away? Ten years away or maybe 20?

Dr. Kadem With counting in terms of pandemics ….

Rob Fraser Those are 80 years apart or something now?

Dr. Kadem Yeah!  Well, honestly, it is difficult to answer because it depends on the human resources. I figured out that doing a project like this with graduate students is not the best strategy because obviously they are taking courses and working on their projects. So my challenge now is to get funding to hire a full time engineer. And then it will be easier to have clear timelines and milestones. What we have done so far is a very good prototype. It’s working. We have MRI images of the system, flow and phase contrast MRI measurements. It’s working, but it’s not there yet. The flow rate is still quite low for example and I’m not satisfied yet. But, if we continue at the same pace, I’m guessing five years is probably realistic.

Rob Fraser Cool. My last question is, “Do you have any advice for our readers?”

Dr. Kadem We have to continue exploring cardiovascular flows because they are really rich. And the bottom line is that our system is really complex, so let me paraphrase a citation: “For of course, the body is a complex machine. It is a vastly complex machine, many, many times more complicated than any machine ever made with hands”. This is interesting, because when you stop here, you figure out that there is not much to do. But then there is this magic last sentence:  “But it’s still a machine”. This means that it’s complex. We all agree. But there must be a way to understand it. It has to follow the laws of physics.

When you think like this, basically, this means that if we understand the flow, this will allow us not only to better predict deviations from the optimal flow, and this will give us new early diagnostic parameters. This will also help us to design better medical devices. And also, this will help us develop other devices. For example, the heart is very good in mixing without turbulence. Some applications here are if you want to design, for example, a system that will mix polymers or things that are fragile. Basically the cardiovascular flow is so rich that it needs first to be further explored, but also explored in a multi-disciplinary approach.

Rob Fraser That’s fascinating, You’re right to think of the human body or other life forms as kind of above machines, At the end of the day, it’s a standalone thing and it has to obey the laws of physics. That’s an interesting way to break that down. Thanks so much for your time and enjoy your evening.

Dr. Kadem Thank you.

Photos credit: Concordia communication

Read Dr. Kadem’s publications citing ViVitro Labs equipment.

Read about other Cardiovascular Pioneers here.

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