Friday, June 5, 2015

Robert Plonsey (1924-2015)

The eminent biomedical engineer Robert Plonsey died on March 14. Readers of the 5th edition of Intermediate Physics for Medicine and Biology will be familiar with Plonsey, as Russ Hobbie and I cite nine of his publications.

I read Plonsey’s classic textbook Bioelectric Phenomena (1969) in graduate school, and I have taught from his book Bioelectricity: A Quantitative Approach with Roger Barr. I discussed previously in this blog his book Bioelectromagnetism with Jaakko Malmivuo.

Plonsey had an enormous impact on my research when I was in graduate school. For example, in 1968 John Clark and Plonsey calculated the intracellular and extracellular potentials produced by a propagating action potential along a nerve axon (The Extracellular Potential Field of a Single Active Nerve Fiber in a Volume Conductor, Biophysical Journal, Volume 8, Pages 842-864). Russ and I outline this calculation--which uses Bessel functions and Fourier transforms--in IPMB’s Homework Problem 30 of Chapter 6. In one of my first papers, Jim Woosley, my PhD advisor John Wikswo, and I extended Clark and Plonsey’s calculation to predict the axon’s magnetic field (Woosley, Roth, and Wikswo, 1985, The Magnetic Field of a Single Axon: A Volume Conductor Model. Mathematical Bioscience, Volume 76, Pages 1-36). I have described Clark and Plonsey’s groundbreaking work before in this blog.

I associate Plonsey most closely with the development of the bidomain model of cardiac tissue. The 1980s was an exciting time to be doing cardiac electrophysiology, and Duke University, where Plonsey worked, was the hub of this activity. Wikswo, Nestor Sepulveda, and I, all at Vanderbilt University, had to run fast to compete with the Duke juggernaut that included Plonsey, Barr, Ray Ideker, Theo Pilkington, and Madison Spach, as well as a triumvirate of then up-and-coming researchers from my generation: Natalia Trayanova, Wanda Krassowska, and Craig Henriquez. To get a glimpse of these times (to me, the “good old days”), read Henriquez’s A Brief History of Tissue Models for Cardiac Electrophysiology (IEEE Transaction on Biomedical Engineering, Volume 61, Pages 1457-1465) published last year.

My first work on the bidomain model was to extend Clark and Plonsey’s calculation of the potential along a nerve axon to an analogous calculation along a cylindrical strand of cardiac tissue, such as a papillary muscle (Roth and Wikswo, 1986, A Bidomain Model for Extracellular Potential and Magnetic Field of Cardiac Tissue. Volume 33, Pages 467-469). I remember what an honor it was for me when Plonsey and Barr cited our paper (and mentioned John and me by name!) in their 1987 article Interstitial Potentials and Their Change with Depth into Cardiac Tissue (Biophysical Journal, Volume 51, Pages 547-555). That was heady stuff for a nobody graduate student who could count his citations on his ten fingers.

One day Wikswo returned from a conference and told us about a talk he heard, by either Plonsey or Barr (I don’t recall which), describing the action current distribution produced by a outwardly propagating wave front in a sheet of cardiac tissue (Plonsey and Barr, 1984, Current Flow Patterns in Two-Dimensional Anisotropic Bisyncytia with Normal and Extreme Conductivities. Biophysical Journal, Volume 45, Pages 557-571). Wikswo realized immediately that their calculations implied the wave front would have a distinctive magnetic signature, which he and Nestor Sepulveda reported in 1987 (Electric and Magnetic Fields From Two-Dimensional Anisotropic Bisyncytia, Biophysical Journal, Volume 51, Pages 557-568).

In another paper, Barr and Plonsey derived a numerical method to solve the bidomain equations including the nonlinear ion channel kinetics (Barr and Plonsey, 1984, Propagation of Excitation in Idealized Anisotropic Two-Dimensional Tissue. Biophysical Journal, Volume 45, Pages 1191-1202). This paper was the inspiration for my own numerical algorithm (Roth, 1991, Action Potential Propagation in a Thick Strand of Cardiac Muscle, Circulation Research, Volume 68, Pages 162-173). In my paper, I cited several of Plonsey’s articles, including one by Plonsey, Henriquez, and Trayanova about an Extracellular (Volume Conductor) Effect on Adjoining Cardiac Muscle Electrophysiology (1988, Medical and Biological Engineering and Computing, Volume 26, Pages 126-129), which shared the conclusion I reached that an adjacent bath can dramatically affect action potential propagation in cardiac tissue. Indeed, Henriquez (Plonsey’s graduate student) and Plonsey were following a similar line of research, resulting in two papers partially anticipating mine (Henriquez and Plonsey, 1990, Simulation of Propagation Along a Cylindrical Bundle of Cardiac Tissue—I: Mathematical Formulation, IEEE Transactions on Biomedical Engineering, Volume 37, Pages 850-860; and Henriquez and Plonsey, 1990, Simulation of Propagation Along a Cylindrical Bundle of Cardiac Tissue—II: Results of Simulation, IEEE Transactions on Biomedical Engineering, Volume 37, Pages 861-875.)

In parallel with this research, Ideker was analyzing how defibrillation shocks affected cardiac tissue, and in 1986 Plonsey and Barr published two papers presenting their saw tooth model (Effect of Microscopic and Macroscopic Discontinuities on the Response of Cardiac Tissue to Defibrillating (Stimulating) Currents, Medical and Biological Engineering and Computing, Volume 24, Pages 130-136; Inclusion of Junction Elements in a Linear Cardiac Model Through Secondary Sources: Application to Defibrillation, Volume 24, Pages 127-144). (It is interesting how many of Plonsey’s papers were published as pairs.) I suspect that if in 1989 Sepulveda, Wikswo and I had not published our article about unipolar stimulation of cardiac tissue (Current Injection into a Two-Dimensional Anisotropic Bidomain, Biophysical Journal, Volume 55, Pages 987-999), one of the Duke researchers—perhaps Plonsey himself--would have soon performed the calculation. (To learn more about the Sepulveda et al paper, read my May 2009 blog entry.)

In January 1991 I visited Duke and gave a talk in the Emerging Cardiovascular Technologies Seminar Series, where I had the good fortune to meet with Plonsey. Somewhere I have a videotape of that talk; I suppose I should get it converted to a digital format. When I was working at the National Institutes of Health in the mid 1990s, Plonsey was a member of an external committee that assessed my work, as a sort of tenure review. I will always be grateful for the positive feedback I received, although it was to no avail because budget cuts and a hiring freeze led to my leaving NIH in 1995. Plonsey retired from Duke in 1996, and our paths didn’t cross again. He was a gracious gentleman who I will always have enormous respect for. Indeed, the first seven years of my professional life were spent traveling down a path parallel to and often intersecting his; to put it more aptly, I was dashing down a trail he had blazed.

Robert Plonsey was a World War Two veteran (we are losing them too fast these days), and a leader in establishing biomedical engineering as an academic discipline. You can read his obituary here and here.

I will miss him.

1 comment:

  1. Thanks for sharing. I've enjoyed working through his book in Roger Barr's Coursera course with the same title.

    (Of course, IPMB would make be an exceptional Coursera course)