In this new book co-editors Drs. Jose Almeida, Ghassan Kassab, Fedor Lurie, and Seshadri Raju blend engineering, clinical medicine, and investigational diagnostics to elevate venous treatment.
Hemodynamics for Surgeons edited by Strandness and Sumner was published in 1975 and quickly fell into the ‘must have’ category for an emerging new cadre of vascular surgeons. Today, the original edition has long been out of print, but used copies still sell for thousands of dollars, a sign of the lasting popularity of the book. In 2018, Dr. Seshadri Raju, himself a giant in the venous field, initiated the publication of a second edition of the book’s venous section. (Arterial and venous disease have grown into distinct subspecialties, and the production of a new edition became less challenging by splitting it into two projects.) Dr. Raju, affectionately called Raj by his colleagues, co-opted three editors, each an acknowledged world authority in clinical aspects, hemodynamics, and diagnostic testing of venous disease. Sumner’s Hemodynamic Guide to Venous Diagnosis and Intervention, edited by Almeida, Kassab, Lurie, and Raju, is set to be a future classic.
Here, Dr. Almeida leads his colleagues in a behind-the-scenes discussion about what is sure to be another enduring contribution to the venous space.
Jose Almeida: Raju, you initiated this project. How did you get involved with venous disease and how did you know Dr. David Sumner, one of the original editors of Hemodynamics for Surgeons?
Dr. Seshadri Raju: I became interested in venous disease as a cardiothoracic and transplant surgeon, so I started attending venous meetings. I had two friends and mentors. One was John Bergan, and the other was David Sumner. Pretty early on, Dr. Bergan told me unless I focussed, I would not make a mark. I didn't think much about it at the time, but later professional circumstances evolved in such a way that I had to choose between transplants and venous disease. Venous disease was more in line with my advancing age. Anybody who has been in transplants will know it is a young man's game. Like football players, transplant surgeons become tired pretty early.
So I decided to take venous disease, and Dr. Sumner was a mentor in that field. I knew him as a personal friend and he was an extraordinary mind, an extraordinary man who helped and encouraged many young people in the venous community. He was intellectually very generous. If you asked him a question, he would take out a notepad and begin writing calculus equations. He would tell you why things were the way they were.
Dr. Almeida: The three of us got phone calls from you one day. You told us you wanted to pay tribute to Dr. Sumner and continue to deliver this essential information to the field. You asked me to take on the clinical side. Ghassan is a biomedical engineer, and he offered a unique perspective on the hemodynamics and basic science perspective on venous disease (collapsible tube, et cetera). And of course, Dr. Lurie’s valve and hemodynamics work and time in the space made him an obvious choice for the project. His contribution is focused mainly on the vascular lab. You called us with a vision for the project, and then in 2018 we all went to St. Louis and met with Mrs. Marty Sumner. Why don't you tell us about your vision?
Dr. Raju: Back when Hemodynamics for Surgeons was in publication, it was the Bible for those of us in practice, and it was a unique book. There were books on the clinical side such as Rutherford's textbook. But if you wanted to be a scientist in vascular surgery, the “Green Book of Sumner and Strandness” was the one to go to. It had three components. It had a very strong basic side, which was first and foremost. The authors explained the basic bioengineering behind the behavior of arterial and particularly venous disease, which was my interest. Then they described the clinical features, and lastly, they went into investigation methods.
The book is a scrolling book. If you read it, your initial impression is that it is not well organized because it's so spread out. But then you read it a second, third, and a fourth time; incidentally, it takes three or four times to absorb everything that is in that book. Sumner had a knack for summarizing the state of the art. He had a knack for telling you what is not known and what needs to be done, all in one chapter. You don't realize it while you are reading it, but then once you are through, you know he has laid the foundation of what we know and also the research path for future progress. It's a very unique book in that way.
Dr. Sumner’s wife, Martha (‘Marty’) had been asking him to redo the book for some time. That was a request from a lot of surgeons and trainees. Dr. Sumner was a very meticulous man, and he didn’t do anything slip short. Either he did it well or not at all. So there was some time spent preparing for the next edition. Unfortunately, his health problems intervened and he never finished the book. After his passing, Mrs. Sumner wished that the book would continue as a memorial to him. So the drive was to propagate what he started and continue his interest.
I knew I couldn't do it alone because it would be an enormous effort and I was at a stage in my life where I would not have been able to do a good job, and also may not have had time to finish it.
So we talked to friends, Bo Eklof and Bob Kistner, to see who might be the right co-editors. You, Dr. Almeida, were a perfect choice. You have a wide base of knowledge, enormous energy, and drive and interest in the disease and in the scientific aspects.
Then we had choices for the basic science and clinical investigational sides as well. Dr. Kassab is undoubtedly one of the best bioengineers today in the country. Dr. Kassab was the final pupil of Dr. Y.C. Fung who is often cited worldwide as a father of bioengineering.
And Fedor of course is well known in the venous field for his contributions to investigational techniques in venous disease including duplex and other techniques. So we collaborated with him, and I believe we came up with the perfect team. I have seen the initial runouts of the book and I would say our dream is about to come true.
Dr. Almeida: Ghassan, when we were charged with this project, you and I spoke a few times to get to know each other. I've seen you speak about your experience with coronary arteries, principles of flow divergence, Murray’s law, and these things that we were all interested in at AVF. As we went back and forth, we discussed the basics of reflux and obstruction in venous hypertension and what it all means. There are so many gaps in our collective knowledge currently. What is venous hypertension? I still don't know exactly what it means. The more you learn about it, the more questions arise. It’s just a rabbit hole that never ends, as we’ve all experienced.
You wrote the first seven chapters of the book. In the first chapter, you really show your depth in mathematics and calculus, and when you showed me how you derive equations, those just went right by me. But as the chapters develop we start seeing collapsible tubes and boundary conditions and looking at the venous system more like a network. There are two areas of focus in the venous treatment space. One is venous obstruction, namely the iliac vein and placing stents. And the other one is saphenous vein reflux and saphenous vein ablation for folks with varicose veins. Those are the two things that we treat most, and we are trying to better understand why we treat disease manifestations, why treatment approaches work, why and when they don’t work, and how to select patients.
So your contribution has been great, it has gotten me to think about things, even iliac vein stenting and flexible stents, a lot differently. For instance, with stents, you hear about the radial and chronic outward force and that the aspect ratio needs to be a perfect circle. But when I started reading your chapters, I realized, of course, the iliac vein outflows into the vena cava, which is typically spherical and flat. So why are we making this vein round and dumping it into an elliptical vein? For all the fuss of getting a perfect circle in the iliac, what does that mean hemodynamically with flow and Poiseuille’s equation? And on the reflux side, what is meaningful reflux?
How does a calf pump handle it? When do you overwhelm the calf pump? There are so many patients who have reflux who don’t have symptoms and others with minimal reflux that have major symptoms.
From your point of view as a biomedical engineer, how did you go through the process of trying to figure out what we as clinicians want out of reflux and obstruction?
Dr. Ghassan Kassab: You’re asking me some granular questions. I’m going to zoom out and then zoom back in. When I first read Dr. Sumner’s book, he seemed to me like an engineer in a white coat. I was very impressed with his ability to handle analytical equations and so on. As Raj mentioned, he knew calculus brilliantly and tried to express ideas quantitatively.
So what makes a surgeon jump into the boots of an engineer? And what makes an engineer try to understand the clinical world? That connects to my mentor Y.C. Fung who Raj mentioned.
Dr. Fung had a very established career as an aeronautical engineer. The reason he moved into biomedical engineering is that his mother developed glaucoma. So at that time, he wanted to study biology and physiology. It was when his mother got sick that he started to read the literature on glaucoma and started to translate that literature for her surgeon, her physician, and his mother. He wrote these long letters back to China to his mother when he was here at Caltech.
Engineers appreciate analytical and mathematical precision. Physiology in the ‘60s had analytical approaches, yet there was still much to be done in terms of expressing things through the laws of physics. The same laws of physics that apply to a shuttle or a bridge apply to our bodies too. So that’s what got his interest.
There is beauty there. There’s cross-fertilization there because we’re not separate. If you look at biomechanics, as the term suggests, bio is life and mechanics is a branch of physics that studies motion and the forces that cause motion. So it’s a combination of the two.
The problems that Jose mentioned such as obstruction and reflux or any problem in general, one has to take a systematic approach to understand. And we call that the biomechanical approach or the bioengineering approach that requires certain pillars.
So let me give you some examples that we’re all familiar with. If an engineer has to design a bridge or a space shuttle or an automobile, they clearly need to understand the structure or the geometry of the system. To us on the medical side, we call that anatomy. So that means you have to really know anatomy intimately. In our case, we seek to understand the vascular system (the irrigation system, if you will) that delivers blood flow.
But I don't mean just generally understanding it. You really have to understand the circuit. It’s like an electrical engineer trying to wire a radio. Unless they know all the resistors and the capacitors, they're not going to be able to produce the kind of function they need. Just generally knowing there is a branch here and there are some side branches is inadequate. The connectivity is important, and the detailed anatomy is important. So that's one pillar.
On top of that, going back to the engineer who is designing a bridge, they have to know the material components of that bridge. Is it stainless steel? Is it copper? Is it cement? On what are you basing the mechanics? What has to sustain and resist the stresses, the loads that are being imposed on it? So those are the mechanic, the material properties.
And in fact, I think an area that’s not well understood even to this day is the material properties of our blood vessels generally, and veins specifically (because they're nonlinear properties of these structures). They are not like stainless steel. The material can change itself, it can adapt. Something that concrete and stainless steel don't do. If you stress those materials, they stay the same.
Here we have very interesting properties. We have time dependent properties. We have viscoelasticity, we have growth and remodeling. If you push more flow through, you’ll get more branches. If you cut down the flow, you lose branches. So all of that—geometry, anatomy, material properties—is absolutely necessary for rational, honest analysis.
Now, to solve an equation mathematically one needs to know what are the initial conditions? Meaning, where does the system start in time? That's important. One also has to know what are the boundary conditions in space?
So you need time and you need space. In the case of the venous system, there are lots of interactions with the surrounding tissue. There’s the calf pump that Jose alluded to, all that’s very important, that’s interacting with the blood vessels. The vessels that are collapsible create very interesting dynamics where collapse is possible in some places, but not in other places.
There is also interaction with the heart obviously, where the venous system ends up draining. What goes on in the right side of the heart is extremely important. What happens with respiration?
That's another boundary condition. The variation and abdominal pressure are other boundary conditions. So those have to be prescribed.
Mathematically if you have an equation that’s first order, then you only can prescribe one condition. If it's second order, you have to prescribe two. If it’s third order, you have to prescribe three, and so on. So if you don’t prescribe enough conditions, you'll have infinitely many solutions. In other words, you didn't constrain it enough. If you constrain it too much, you have no solution.
So these are mathematical, what we call, well-posed boundary value problems. A well-posed boundary value problem has just the right conditions for a solution to be predictive and to be realistic. So these are all the ingredients.
The goal of this book is to point out the gaps and where is it necessary to add more information. I’ve learned a lot from Fedor’s work. As engineers, we can do computational modeling and understand, and develop mechanics. But without Fedor’s seminal measurements that are based on patient data to help us inform our models and help us be critical of our predictions, we can’t make advances.
So my hope and my message in this and my excitement in joining a group of great people is to bring more attention to the need to collaborate between the clinicians, the scientists, the researchers, and the engineers because these problems are so complex it requires a convergence of many fields.
Dr. Almeida: One thing we wanted to do was preserve the spirit of the Sumner book. We all incorporated some of the original writing and then added on newer material.
When you go through the original book for the first time, it is a strange organization in the way it reads, but the writing is brilliant. To this day, I’ve never read anything like it, the way it is put together and the amount of information Sumner and Strandness got from very small clinical studies. They made brilliant deductions from small experiments. I think we did preserve the original spirit of Sumner and introduced what we know now, and of course, I have many more questions.
Fedor, you’ve written a lot on duplex and about nuanced things such as the time of day when you study people and whether they're upright or supine. You’ve done a lot of valve work. You were out in Hawaii with Bob Kistner and Bo Eklof, two of the giants in the field, seeing what went on clinically.
Tell us how you approached your piece of the book?
Dr. Fedor Lurie: Well, Jose thanks. It’s interesting that you turn the discussion around exactly in the direction that I was thinking about.
You’re right, my entire career was influenced very heavily by a few people. I was fortunate to work closely with Bob Kistner for a number of years. But even before that, I was given veins when I was a junior faculty in the vascular surgery department.
I met Dr. Sumner in 1996. As Raj beautifully described, he immediately became my mentor and his mentorship style is probably impossible to replicate. He simply became my friend. Even more, Marty, his wife became friends with Galina, my wife, and we had very scientific conversations often discussed softly at the dinner table.
David structured discussions of vascular disease into a debate between biology versus physics. And every single time I tried to make some convincing argument he would question it and say, “How do you know that?”
When I was preparing my first paper, I sent a draft to him and within about 20 minutes, I got the fax back. A page with no words, just equations pointing out every single measurement error I could make.
I tried to get that spirit in my chapters because Dr. Sumner focused his thoughts and writings not just on what we know, but also where we could make an error. Where is it that we always stray from what we know? How can we advance the field? By no means is it the only way that Dr. Sumner did things, but that willingness to question what could be wrong was very important for me to keep in the spirit of the chapter on imaging.
Since I first met David, he was a photographer. He took pictures of everything he saw, and at one point I asked him, “What is with so many pictures? What are we trying to do?” And he said, “I’m trying to see what’s real versus what I think. Every time I see a flower and I think it's big like this or like that, I take a picture, and when I look at the picture, it’s actually not what I thought before.”
Later on, he started painting, and his paintings are also in a way trying to show you what’s true in nature, what’s beautiful, what’s not. He was always on this quest to find out what is true and what is a perception. That’s the spirit of Dr. Sumner’s writing that I tried to keep in my chapters.
Dr. Almeida: The primary audience for this is venous clinicians. But as we know the venous space has become very device-centric. There are a lot of stakeholders now. Medicine is big business and there are all kinds of middlemen and people looking at it from different angles as far as what to reimburse, how to innovate, and how to get through the FDA process. It has become very difficult.
Part of what we want for the book is for engineers to look at it. We thought both detailed and also broad enough so that device manufacturers could look at it and think, “Now we see where they're having issues, and here’s a basic science basis illustrated by a biomedical engineer on how to look at this and solve the problems.”
We cover some procedures and hope that will be valuable for engineers. I.e. the options for reflux are these thermal and non-thermal devices; you can do traditional surgery; you can do sclerotherapy. Here are the problems with recurrence. How do you select the patients? Where does it work? Where does it not?
Same with the obstruction side, which is more in its infancy. What do we look for in a stent? What are the material characteristics that are more suitable for the venous system? How does it interact with the arterial system? What is the long-term follow-up? What are the complications? What happens to these stents over time? What if they’re post-thrombotic? So in the book we go into thrombosis, we go into primary disease which is non-thrombotic, and secondary disease which is post-thrombotic.
We look at the heart. I learned things working on this book because I didn’t know that the right atrium also has an active “suction function.” I did not know that. I thought it was a passive organ that accepted preload and then the ventricle took on all the mechanical duties of contraction.
Ghassan, how do you think a biomedical audience will respond to this book? Also, what are the gaps in this edition that we can work on in the future?
Dr. Kassab: My feeling is that because of the collaborative nature here, where we have clinicians and engineers working together, that will set the pace. The fact that we’re saying things that engineers can relate to is wonderful because it invites them in.
I learned a great deal from your and Fedor’s chapters, things I didn't know. Similar to you, I feel a next edition will be warranted sometime in the future as we integrate the knowledge and pull it all together, as we understand each other’s side better, and talk to each other more. The essence of this is making it so the conversations and conferences have cross-fertilization as opposed to engineers standing in their corner and clinicians doing their thing. We really need to interface a great deal, and the more that the engineer learns about the clinical world, the better.
By physicians pulling in engineers and helping them understand what the problems are, what things work, and more importantly, what things don’t work, we can talk about the solutions.
What you have as a clinician that’s very essential is the question. All science starts with a question and the better the question, the better the science. So someone like yourself, who is onsite can come up with the questions. Every patient is a question. So you can pose that question better than any engineer can.
Now what the engineer can do is help you come up with an engineering answer to that question. Some answers are more complex, some are simpler, some are more easily integrated into the choreography of practice, others aren’t, and that’s the art. But that’s the beauty of this—the more we do to bring the two together, the better, and I think the book is a great start.
Dr. Lurie: I think Ghassan outlines it very nicely. As clinicians, we do have questions. We also have observations but we are amateurs in explaining physical meaning. In reality, changing the geometry is the main thing we do as vascular surgeons. We change the anatomy to change hemodynamics and we really need professionals to bridge what we do mechanically and what the result is going to be clinically.
In my life, it was another great fortune to meet Ghassan because that was a missing link. His work really bridged that gap between what we see and what that means. So I think that this collaboration and this book may start a closer collaboration between vascular surgery and physics, leading to better science.
MEET THE EDITORS
Jose Almeida, MD practices endovascular venous surgery in an academic private practice in Miami. He serves as Voluntary Professor of Surgery at the University of Miami School of Medicine and is the course director of the International Vein Congress (IVC).
Ghassan Kassab, PhD is a highly-awarded bioengineer and inventor. He was in various academic positions previously until about eight years when he arrived back in San Diego and started California Medical Innovations Institute, a nonprofit focused on the clinical translation of emerging technologies.
Fedor Lurie, PhD, MD has been through a number of academic appointments for vascular surgery through the years. Currently, he is Associate Director of the Jobst Vascular Institute, and Adjunct Research Professor at the Section of Vascular Surgery, University of Michigan, Ann Arbor. His clinical and research activities focus on venous and lymphatic disorders and diagnostic ultrasound and imaging.
Seshadri Raju, MD is a surgeon trained in cardiothoracic surgery and vascular surgery. He was on the teaching staff of the University of Mississippi Medical Center and retired as Emeritus Professor. Before retirement, his main field of interest was transplantation. He performed the first successful lung transplant in this country, and headed one of the earliest clinical transplant programs with multi-organ capability. He was a founding member of the American Venous Forum. He is widely credited for pioneering venous stent technology with over 250 peer-reviewed publications. His clinical practice is at the Rane Center in Jackson, Mississippi.
Sumner’s Hemodynamic Guide to Venous Diagnosis and Intervention will be published by CineMed in digital print formats. Copies will be available for