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Interview: Dominik Obrist on biomedical fluid dynamicist approach to determining mechanistic causes

August 18th, 2015

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Dr. Dominik Obrist

Dr.  Dominik Obrist

Dominik Obrist is Professor for Cardiovascular Engineering at the ARTORG Center for Biomedical Engineering Research of the University Bern. His present research activities encompass several aspects of cardiovascular fluid mechanics (e.g. aortic valves, microcirculation) as well as other biomedical flow systems (e.g. gastric mixing, respiratory flow).

Dr. Obrist holds a degree in mechanical engineering of ETH Zurich and earned his doctoral degree in 2000 at the Department of Applied Mathematics of the University of Washington (Seattle, USA). In 2011, Dominik Obrist earned the venia legendi (Habilitation) at ETH Zurich with a treatise on the fluid mechanics of the inner ear.

Dr. Obrist toured ViVitro Labs in Victoria recently.  Lab Manager, Rob Fraser Msc. (RF), spoke with Dr. Obrist (DO) about his lab work in Bern, similarities in measuring different body fluid flows, and recent highlights.

RF: What are you working on regarding aortic and mitral valve flow?

DO:  We’re mostly looking at tissue valves.  We’re interested in understanding why some valves perform better than others.  We have set up multiple flow loops that allow us to measure different things: be it global quantities such as pressure gradient, flow rate or regurgitation, or local quantities such as flow structures, coherent structures in the flow and opening/closing kinematics..

About 80% of the work is on aortic valves and 20% is on mitral valves.  We’re extremely close to our clinical partners: heart surgeons and cardiologists.  Usually the questions we try to answer come directly from our clinical partners.  They come and ask “Please take a look at this problem.  Will this work? Is this  a good or a bad idea?”  This is what drives our research.

RF: How do gastric mixing and respiratory flow fit in?

DO:  (Laughs) Oh! You were really taking a careful look at our website. Let me explain: I’m a biomedical flow dynamicist.   I am interested in anything that flows in the human body.  Obviously the cardiovascular system is the most prominent flow, but I have no hesitation in looking at any of the other fluid flows.  The gastric system contains also some fluid.  Apart from that the gastric system is an interesting concept:  it is a pumping or mixing device efficiently operating at mostly very low Reynolds numbers.  Understanding these mixing and pumping processes, might help in some other places, which I don’t know yet, but I eventually will. Perhaps for the design of micro-pumps?

RF:  Do the projects ever mix or overlap?

DO:  I’m trying to mix and overlap them in my head. I try to have the big picture.   A lot of the methodologies are the same.  If you want to measure velocity, it doesn’t really matter if it’s velocity in the inner ear or in the heart. The methods are the same. The theory behind the physics is the same. It’s just a different application.  That’s my approach.

I have no background in anatomy or any formal medical education. I think that’s maybe something that helps.  It’s a classical engineering approach.  You just know your tools and how they work.  The only unique thing you have is a certain openness to listen to medical doctors and they will be happy to explain to you the involved anatomy and physiology.  That’s what I find fascinating about doing this kind of biomedical engineering.

RF: What are some highlights of the research you have conducted so far?

DO: A recent highlight is that we are the first and only full 3D PIV flow measurement past an aortic valve with our new tomographic PIV system.  I don’t think anyone has ever done that before.  We saw some interesting things, but we haven’t understood them yet.

Another nice project was the micro-PIV study in the hinge region of a mechanical tri-leaflet valve.  We made a transparent full scale mock-up of the valve.  We made the ring of the valve very clear with rapid prototyping material.  We used the original leaflets but manufactured the valve ring out of a transparent material with rapid prototyping so we could actually look through the ring. This was a micro PIV experiment in the gap of the hinges.  Just like Yoganathan did with the St. Jude Regent valve.  It was essentially the same experiment just on a different valve.

RF:  What VL services/equipment do you use and how did they help your work?

DO:  The SuperPump is a very reliable, useful workhorse in our lab.  At times I’m scared of what would happen if it breaks.  Because if it breaks, a lot of projects would be halted.  We have other pumping devices which can do similar things, but the SuperPump is the only one which is really Plug and Play.

RF:  Do you have other pulsatile pumps? 

DO:  For one set up we’ve used just a piston pump with our own set-up.  It does the job that it needs to do, but it’s nowhere as easy and smooth as the SuperPump.

RF:  Do you find it easier for your students to use the SuperPump instead of internally built equipment?

DO:  Yes.  Absolutely.  Very much so.

RF: What are your future plans for the research lab?

DO:  My lab is a relatively young lab.  We are currently establishing a baseline for all our research activities.  We need to have 2-3 flow-loops going and we need to fully understand them.  We are now in the process of acquiring baseline data against which we can compare everything else.  We are playing around with different models, for instance, with aortic roots with different compliances or with models with coronary arteries.  We want to see all of this has an influence on valve performance.

Once we have a baseline we will be able to make some very specific statements about different valve types.  Why we believe this one behave like this and that one behaves like that.  We would like to find the mechanistic cause for certain clinical behaviors.   For example, surgeons see that some valve type fails after only 5 years.  Why does it fail after 5 years while another one fails after 15, even though they both look more or less the same? We would like to give precise, mechanistic answers to such questions.

RF:  That is getting into brand differences. Do you see any struggles with manufacturers over publishing papers to say why one is better than another?

DO: We never go and say one is better than another.  We always say, “This one does this.” We never say, “This one is better”. I think this would miss the point anyway.

RF: Do you have any advice for academic faculties creating a new test lab?

DO: I would tell them, “It’s more complicated than you think. “ The first time I saw a heart valve I thought: “This is such as simple device. It’s not really doing anything.  It’s just some tissue. Some stupid soft tissue opening and closing.”  But the more you work with it, the more you realize how complex it is.

When we tried to set up our first flow loop, I expected it would be very, very simple.  You just control the motion of the piston, that’s it. Only later, you start to realize that you also need to tune compliance, resistance and so many other things.  That’s definitely a lesson I had to learn.

Read more interviews with Cardiovascular Pioneers.


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