John Wikswo
Encyclopedia
John Peter Wikswo, Jr. is a biological physicist at Vanderbilt University
. He was born in Lynchburg
, Virginia
, United States
.
Wikswo is noted for his work on biomagnetism
and cardiac electrophysiology
.
, where he worked under physicist William M. Fairbank
, studying magnetocardiography
.
, where he set up a laboratory to study Living State Physics. In 1980, he made the first measurement of the magnetic field of an isolated nerve, by threading the a frog sciatic nerve through a wire-wound, ferrite-core toroid and detecting the induced current using a SQUID
magnetometer
.
At the same time, Wikswo and Ken Swinney calculated the magnetic field of a nerve axon.
This work was followed a few years later by the first detailed comparison of the measured and calculated magnetic field produced by a single nerve axon.
In a related line of study, Wikswo collaborated with Vanderbilt Professor John Barach to analyze the information content of biomagnetic versus bioelectric signals.
These studies led to the discovery of the virtual cathode effect in cardiac tissue: during electrical stimulation, the action potential wave front originated farther from the electrode in the direction perpendicular to the myocardial fibers than in the direction parallel to them.
In parallel with these experimental studies, Wikswo analyzed the virtual cathode effect theoretically using the bidomain
model, a mathematical model of the electrical properties of cardiac tissue that takes into account the anisotropic properties of both the intracellular and extracellular spaces. He first used the bidomain model to interpret biomagnetic measurements from strands of cardiac tissue.
Wikswo realized that the property of unequal anisotropy ratios in cardiac tissue (the ratio of electrical conductivity in the directions parallel and perpendicular to the myocardial fibers is different in the intracellular and extracellular spaces) has important implications for the magnetic field associated with a propagating action potential wave front in the heart. With Nestor Sepulveda, Wikswo use the finite element method
to calculate the distinctive fourfold symmetric magnetic field pattern produced by an outwardly propagating wave front.
Unequal anisotropy ratios has even an even greater impact during electrical stimulation of the heart. Again using the finite element model, Wikswo, Roth and Sepulveda predicted the transmembrane potential distribution around a unipolar electrode passing current into a passive, two-dimensional sheet of cardiac tissue.
They found that the region of depolarization
under a cathode
extends farther in the direction perpendicular to the fibers than parallel to the fibers, a shape that Wikswo named the dog-bone. This prediction immediately explained the virtual cathode effect found experimentally in the dog heart; they were observing the dog-bone shaped virtual cathode. Later simulations using an active, time-dependent bidomain model confirmed this conclusion.
The calculation of the transmembrane potential by a unipolar electrode resulted in another prediction: regions of hyperpolarization adjacent to the cathode in the direction parallel to the myocardial fibers. Reversal of the stimulus polarization provided a mechanism for anodal stimulation of cardiac tissue. In order to test this prediction experimentally, Wikswo mastered the technique of optical mapping using voltage sensitive dyes, allowing the measurement of transmembrane potential using optical methods. With Marc Lin, Wikswo made high resolution measurements of excitation following stimulation through a unipolar electrode in a rabbit heart, and confirmed four mechanisms of electrical stimulation—cathode make, cathode break, anode make, and anode break—that had been predicted by bidomain calculations.
(Cathode and anode refer to the polarity of the stimulus, and make and break indicate if the excitation occurred following the start or end of the stimulus pulse.) Later experiments using this technique led to the prediction of a new type of cardiac arrhythmia, which Wikswo named quatrefoil reentry
.
As is characteristic of Wikswo's work, he simultaneously developed theoretical methods to image a two-dimensional current density distribution from magnetic field measurements.
In 2001 he founded the Vanderbilt Institute for Integrative Biosystems Research and Education (VIIBRE) to foster and enhance interdisciplinary research in the biophysical sciences and bioengineering at Vanderbilt.
Vanderbilt University
Vanderbilt University is a private research university located in Nashville, Tennessee, United States. Founded in 1873, the university is named for shipping and rail magnate "Commodore" Cornelius Vanderbilt, who provided Vanderbilt its initial $1 million endowment despite having never been to the...
. He was born in Lynchburg
Lynchburg
Lynchburg or Lynchburgh may refer to:*Lynchburg, California*Lynchburg, Mississippi*Lynchburg, Missouri*Lynchburg, Ohio*Lynchburg, South Carolina*Lynchburg, Tennessee*Lynchburg, Texas*Lynchburg, Virginia...
, Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
.
Wikswo is noted for his work on biomagnetism
Biomagnetism
Biomagnetism is the phenomenon of magnetic fields produced by living organisms; it is a subset of bioelectromagnetism. The study of the biological effects of magnetic fields is magnetobiology...
and cardiac electrophysiology
Cardiac electrophysiology
Cardiac electrophysiology is the science of elucidating, diagnosing, and treating the electrical activities of the heart. The term is usually used to describe studies of such phenomena by invasive catheter recording of spontaneous activity as well as of cardiac responses to programmed electrical...
.
Graduate school
In the 1970s, Wikswo was a graduate student at Stanford UniversityStanford University
The Leland Stanford Junior University, commonly referred to as Stanford University or Stanford, is a private research university on an campus located near Palo Alto, California. It is situated in the northwestern Santa Clara Valley on the San Francisco Peninsula, approximately northwest of San...
, where he worked under physicist William M. Fairbank
William M. Fairbank
William Martin Fairbank is an American physicist known in particular for his work on liquid helium....
, studying magnetocardiography
Magnetocardiography
Magnetocardiography is a technique to measure the magnetic fields produced by electrical activity in the heart using extremely sensitive devices such as the Superconducting Quantum Interference Device...
.
Biomagnetism
In 1977 he became an Assistant Professor in the Department of Physics and Astronomy at Vanderbilt UniversityVanderbilt University
Vanderbilt University is a private research university located in Nashville, Tennessee, United States. Founded in 1873, the university is named for shipping and rail magnate "Commodore" Cornelius Vanderbilt, who provided Vanderbilt its initial $1 million endowment despite having never been to the...
, where he set up a laboratory to study Living State Physics. In 1980, he made the first measurement of the magnetic field of an isolated nerve, by threading the a frog sciatic nerve through a wire-wound, ferrite-core toroid and detecting the induced current using a SQUID
SQUID
A SQUID is a very sensitive magnetometer used to measure extremely weak magnetic fields, based on superconducting loops containing Josephson junctions....
magnetometer
Magnetometer
A magnetometer is a measuring instrument used to measure the strength or direction of a magnetic field either produced in the laboratory or existing in nature...
.
At the same time, Wikswo and Ken Swinney calculated the magnetic field of a nerve axon.
This work was followed a few years later by the first detailed comparison of the measured and calculated magnetic field produced by a single nerve axon.
In a related line of study, Wikswo collaborated with Vanderbilt Professor John Barach to analyze the information content of biomagnetic versus bioelectric signals.
Cardiac electrophysiology
One of Wikswo's most important contributions to science is his work in cardiac electrophysiology. In 1987 he began collaborating with doctors at the Vanderbilt Medical School, including Dan Roden, to study electrical propagation in the dog heart.These studies led to the discovery of the virtual cathode effect in cardiac tissue: during electrical stimulation, the action potential wave front originated farther from the electrode in the direction perpendicular to the myocardial fibers than in the direction parallel to them.
In parallel with these experimental studies, Wikswo analyzed the virtual cathode effect theoretically using the bidomain
Bidomain
The bidomain model is a mathematical model of the electrical properties of cardiac muscle that takes into account the anisotropy of both the intracellular and extracellular spaces.The bidomain model was developed in the late 1970s....
model, a mathematical model of the electrical properties of cardiac tissue that takes into account the anisotropic properties of both the intracellular and extracellular spaces. He first used the bidomain model to interpret biomagnetic measurements from strands of cardiac tissue.
Wikswo realized that the property of unequal anisotropy ratios in cardiac tissue (the ratio of electrical conductivity in the directions parallel and perpendicular to the myocardial fibers is different in the intracellular and extracellular spaces) has important implications for the magnetic field associated with a propagating action potential wave front in the heart. With Nestor Sepulveda, Wikswo use the finite element method
Finite element method
The finite element method is a numerical technique for finding approximate solutions of partial differential equations as well as integral equations...
to calculate the distinctive fourfold symmetric magnetic field pattern produced by an outwardly propagating wave front.
Unequal anisotropy ratios has even an even greater impact during electrical stimulation of the heart. Again using the finite element model, Wikswo, Roth and Sepulveda predicted the transmembrane potential distribution around a unipolar electrode passing current into a passive, two-dimensional sheet of cardiac tissue.
They found that the region of depolarization
Depolarization
In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential...
under a cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
extends farther in the direction perpendicular to the fibers than parallel to the fibers, a shape that Wikswo named the dog-bone. This prediction immediately explained the virtual cathode effect found experimentally in the dog heart; they were observing the dog-bone shaped virtual cathode. Later simulations using an active, time-dependent bidomain model confirmed this conclusion.
The calculation of the transmembrane potential by a unipolar electrode resulted in another prediction: regions of hyperpolarization adjacent to the cathode in the direction parallel to the myocardial fibers. Reversal of the stimulus polarization provided a mechanism for anodal stimulation of cardiac tissue. In order to test this prediction experimentally, Wikswo mastered the technique of optical mapping using voltage sensitive dyes, allowing the measurement of transmembrane potential using optical methods. With Marc Lin, Wikswo made high resolution measurements of excitation following stimulation through a unipolar electrode in a rabbit heart, and confirmed four mechanisms of electrical stimulation—cathode make, cathode break, anode make, and anode break—that had been predicted by bidomain calculations.
(Cathode and anode refer to the polarity of the stimulus, and make and break indicate if the excitation occurred following the start or end of the stimulus pulse.) Later experiments using this technique led to the prediction of a new type of cardiac arrhythmia, which Wikswo named quatrefoil reentry
Quatrefoil reentry
Quatrefoil reentry is a type of cardiac arrhythmia that consists of two adjacent figure-of-eight reentrant circuits.Quatrefoil reentry was predicted by bidomain simulations in 1991and observed experimentally in 1999....
.
SQUID magnetometers
In the 1990s, Wikswo began developing high spatial resolution SQUID magnetometers for mapping the magnetic field, to use in both biomagnetic studies and in non-destructive testing.As is characteristic of Wikswo's work, he simultaneously developed theoretical methods to image a two-dimensional current density distribution from magnetic field measurements.
VIIBRE
In the first decade of the 21st century, Wikswo's research has emphasized the development and application of micro- and nano-scale devices for instrumenting and controlling single cells.In 2001 he founded the Vanderbilt Institute for Integrative Biosystems Research and Education (VIIBRE) to foster and enhance interdisciplinary research in the biophysical sciences and bioengineering at Vanderbilt.
Brief curriculum vitae
- 1970 B.A., Physics, University of VirginiaUniversity of VirginiaThe University of Virginia is a public research university located in Charlottesville, Virginia, United States, founded by Thomas Jefferson...
- 1973 M.S., Physics, Stanford UniversityStanford UniversityThe Leland Stanford Junior University, commonly referred to as Stanford University or Stanford, is a private research university on an campus located near Palo Alto, California. It is situated in the northwestern Santa Clara Valley on the San Francisco Peninsula, approximately northwest of San...
- 1975 Ph.D., Physics, Stanford UniversityStanford UniversityThe Leland Stanford Junior University, commonly referred to as Stanford University or Stanford, is a private research university on an campus located near Palo Alto, California. It is situated in the northwestern Santa Clara Valley on the San Francisco Peninsula, approximately northwest of San...
- 1975-1977 Research Fellow in Cardiology, Stanford University School of MedicineStanford University School of MedicineStanford University School of Medicine is a leading medical school located at Stanford University Medical Center in Stanford, California. Originally based in San Francisco, California as Cooper Medical College, it is the oldest continuously running medical school in the western United States...
- 1977-1982 Assistant Professor of Physics, Vanderbilt UniversityVanderbilt UniversityVanderbilt University is a private research university located in Nashville, Tennessee, United States. Founded in 1873, the university is named for shipping and rail magnate "Commodore" Cornelius Vanderbilt, who provided Vanderbilt its initial $1 million endowment despite having never been to the...
- 1982-1988 Associate Professor of Physics, Vanderbilt UniversityVanderbilt UniversityVanderbilt University is a private research university located in Nashville, Tennessee, United States. Founded in 1873, the university is named for shipping and rail magnate "Commodore" Cornelius Vanderbilt, who provided Vanderbilt its initial $1 million endowment despite having never been to the...
- 1988–present Professor of Physics, Vanderbilt UniversityVanderbilt UniversityVanderbilt University is a private research university located in Nashville, Tennessee, United States. Founded in 1873, the university is named for shipping and rail magnate "Commodore" Cornelius Vanderbilt, who provided Vanderbilt its initial $1 million endowment despite having never been to the...
- 2001–present Gordon A. Cain University Professor, Vanderbilt UniversityVanderbilt UniversityVanderbilt University is a private research university located in Nashville, Tennessee, United States. Founded in 1873, the university is named for shipping and rail magnate "Commodore" Cornelius Vanderbilt, who provided Vanderbilt its initial $1 million endowment despite having never been to the...
- 2001–present Professor of Biomedical Engineering, Vanderbilt UniversityVanderbilt UniversityVanderbilt University is a private research university located in Nashville, Tennessee, United States. Founded in 1873, the university is named for shipping and rail magnate "Commodore" Cornelius Vanderbilt, who provided Vanderbilt its initial $1 million endowment despite having never been to the...
- 2001–present Professor of Molecular Physiology and Biophysics, Vanderbilt UniversityVanderbilt UniversityVanderbilt University is a private research university located in Nashville, Tennessee, United States. Founded in 1873, the university is named for shipping and rail magnate "Commodore" Cornelius Vanderbilt, who provided Vanderbilt its initial $1 million endowment despite having never been to the...
- 2001–present Director, Vanderbilt Institute for Integrative Biosystems Research and Education
- 2005–present A.B. Learned Professor in Living State Physics, Vanderbilt UniversityVanderbilt UniversityVanderbilt University is a private research university located in Nashville, Tennessee, United States. Founded in 1873, the university is named for shipping and rail magnate "Commodore" Cornelius Vanderbilt, who provided Vanderbilt its initial $1 million endowment despite having never been to the...
Awards
| Year | Award |
|---|---|
| 1980–1982 | Alfred P. Sloan Research Fellow |
| 1984 | IR-100 Award for Neuromagnetic Current Probe |
| 1990 | Fellow, American Physical Society American Physical Society The American Physical Society is the world's second largest organization of physicists, behind the Deutsche Physikalische Gesellschaft. The Society publishes more than a dozen scientific journals, including the world renowned Physical Review and Physical Review Letters, and organizes more than 20... |
| 1999 | Fellow, American Institute for Medical and Biological Engineering American Institute for Medical and Biological Engineering The American Institute for Medical and Biological Engineering is an organization of biomedical engineers, which focuses on taking principles of engineering to and applying them to improve the medical and biological engineering fields... |
| 2001 | Fellow, American Heart Association American Heart Association The American Heart Association is a non-profit organization in the United States that fosters appropriate cardiac care in an effort to reduce disability and deaths caused by cardiovascular disease and stroke. It is headquartered in Dallas, Texas... |
| 2005 | Fellow, Biomedical Engineering Society |
| 2006 | Fellow, Heart Rhythm Society Heart Rhythm Society The Heart Rhythm Society is an international non-profit organization that promotes education and advocacy for cardiac arrhythmia professionals and patients. The Society was founded in 1979 and counted 5,100 members from over 70 countries as of January, 2009... |