John Wikswo

Last updated
John Wikswo
Born (1949-10-06) October 6, 1949 (age 72)
Lynchburg, Virginia, United States
NationalityAmerican
Scientific career
Fields Biological Physics
Institutions Vanderbilt University

John Peter Wikswo, Jr. (born October 6, 1949) is a biological physicist at Vanderbilt University. He was born in Lynchburg, Virginia, United States.

Contents

Wikswo is noted for his work on biomagnetism and cardiac electrophysiology.

Graduate school

In the 1970s, Wikswo was a graduate student at Stanford University, where he worked under physicist William M. Fairbank, studying magnetocardiography.

Biomagnetism

In 1977 he became an assistant professor in the Department of Physics and Astronomy at Vanderbilt University, 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. [1] At the same time, Wikswo and Ken Swinney calculated the magnetic field of a nerve axon. [2] 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. [3]

In a related line of study, Wikswo collaborated with Vanderbilt Professor John Barach to analyze the information content of biomagnetic versus bioelectric signals. [4] [5] [6]

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. [7] 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. [8]

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. [9] 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. [10]

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. [11] 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. [12]

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. [13] (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. [14]

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. [15] [16] [17] As is characteristic of Wikswo's work, he simultaneously developed theoretical methods to image a two-dimensional current density distribution from magnetic field measurements. [18]

VIIBRE

In the first two decades 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. [19] 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. Wikswo refocused his research on systems biology, building microfabricated devices for measuring cellular properties and developing mathematical models of cellular signaling. He has designed organ-on-a-chip devices containing small populations of cells to fill the gaps between cell cultures and animals models, for use in pharmacology and toxicology. This work led to a second R&D 100 Award for the MultiWell MicroFormulator, which delivers and removes cell culture media to each of the 96 wells of a microwell plate for toxicology research.

Other positions

He also serves on the scientific advisory boards of Hypres Inc. and CardioMag Imaging Inc. [20]

Brief curriculum vitae

Awards

YearAward
1980–1982Alfred P. Sloan Research Fellow
1984IR-100 Award for Neuromagnetic Current Probe
1989Fellow, American Physical Society
1999Fellow, American Institute for Medical and Biological Engineering
2001Fellow, American Heart Association
2005Fellow, Biomedical Engineering Society
2006Fellow, Heart Rhythm Society
2008Fellow, IEEE
2017R&D 100 Award for the MultiWell MicroFormulator

Related Research Articles

Cavity magnetron Device for generating microwaves

The cavity magnetron is a high-power vacuum tube used in early radar systems and currently in microwave ovens and linear particle accelerators. It generates microwaves using the interaction of a stream of electrons with a magnetic field while moving past a series of cavity resonators, which are small, open cavities in a metal block. Electrons pass by the cavities and cause microwaves to oscillate within, similar to the functioning of a whistle producing a tone when excited by an air stream blown past its opening. The resonant frequency of the arrangement is determined by the cavities' physical dimensions. Unlike other vacuum tubes, such as a klystron or a traveling-wave tube (TWT), the magnetron cannot function as an amplifier for increasing the intensity of an applied microwave signal; the magnetron serves solely as an oscillator, generating a microwave signal from direct current electricity supplied to the vacuum tube.

Electroporation Method in molecular biology to introduce DNA into other hosts

Electroporation, or electropermeabilization, is a microbiology technique in which an electrical field is applied to cells in order to increase the permeability of the cell membrane, allowing chemicals, drugs, electrode arrays or DNA to be introduced into the cell. In microbiology, the process of electroporation is often used to transform bacteria, yeast, or plant protoplasts by introducing new coding DNA. If bacteria and plasmids are mixed together, the plasmids can be transferred into the bacteria after electroporation, though depending on what is being transferred, cell-penetrating peptides or CellSqueeze could also be used. Electroporation works by passing thousands of volts across suspended cells in an electroporation cuvette. Afterwards, the cells have to be handled carefully until they have had a chance to divide, producing new cells that contain reproduced plasmids. This process is approximately ten times more effective in increasing cell membrane's permeability than chemical transformation.

Magnetometer Device that measures magnetism

A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, one that measures the direction of an ambient magnetic field, in this case, the Earth's magnetic field. Other magnetometers measure the magnetic dipole moment of a magnetic material such as a ferromagnet, for example by recording the effect of this magnetic dipole on the induced current in a coil.

Magnetoencephalography Mapping brain activity by recording magnetic fields produced by currents in the brain

Magnetoencephalography (MEG) is a functional neuroimaging technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain, using very sensitive magnetometers. Arrays of SQUIDs are currently the most common magnetometer, while the SERF magnetometer is being investigated for future machines. Applications of MEG include basic research into perceptual and cognitive brain processes, localizing regions affected by pathology before surgical removal, determining the function of various parts of the brain, and neurofeedback. This can be applied in a clinical setting to find locations of abnormalities as well as in an experimental setting to simply measure brain activity.

Bioelectromagnetics, also known as bioelectromagnetism, is the study of the interaction between electromagnetic fields and biological entities. Areas of study include electromagnetic fields produced by living cells, tissues or organisms, the effects of man-made sources of electromagnetic fields like mobile phones, and the application of electromagnetic radiation toward therapies for the treatment of various conditions.

Magnetocardiography Technique to measure the magnetic fields produced by electrical activity in the heart

Magnetocardiography (MCG) is a technique to measure the magnetic fields produced by electrical currents in the heart using extremely sensitive devices such as the superconducting quantum interference device (SQUID). If the magnetic field is measured using a multichannel device, a map of the magnetic field is obtained over the chest; from such a map, using mathematical algorithms that take into account the conductivity structure of the torso, it is possible to locate the source of the activity. For example, sources of abnormal rhythms or arrhythmia may be located using MCG.

TNNT1 Protein-coding gene in the species Homo sapiens

Slow skeletal muscle troponin T (sTnT) is a protein that in humans is encoded by the TNNT1 gene.

Frans Michel Penning Dutch physicist

Frans Michel Penning was a Dutch experimental physicist. He received his PhD from the University of Leiden in 1923, and studied low pressure gas discharges at the Philips Laboratory in Eindhoven, developing new electron tubes during World War II. Many detailed observations of gas ionization were done with colleagues, finding notable results for helium and magnetic fields. He made precise measurements of Townsend discharge coefficients and cathode voltage fall. Penning made important contributions to the advancement of high resolution mass spectrometry.

Magnetic field imaging

Magnetic Field Imaging (MFI) is a non-invasive and side-effect-free cardiac diagnostic method. In more recent technology, magnetocardiography (MCG) has become the clinically predominant application for recording the heart's magnetic signals. that detects and records the electromagnetic signals that are associated with the heartbeat using a multi-channel magnetic sensor array. The electric signals are known from the ECG. In the 1990s and beyond, more recent technology has supplanted the MFI, particularly MCG. Through clinical research in Europe, Asia, and the U.S., MCG has been proven to have practical application for diagnosis of cardiac disease, and has become the clinically predominant application for recording the heart's magnetic signals. In comparison to MCG, MFI, among others, records the whole relevant area above the chest of the person.

Potassium channel blocker Several medications that disrupt movement of K+ ions

Potassium channel blockers are agents which interfere with conduction through potassium channels.

Nanoarchitectures for lithium-ion batteries are attempts to employ nanotechnology to improve the design of lithium-ion batteries. Research in lithium-ion batteries focuses on improving energy density, power density, safety, durability and cost.

The bidomain model is a mathematical model to define the electrical activity of the heart. It consists in a continuum (volume-average) approach in which the cardiac mictrostructure is defined in terms of muscle fibers grouped in sheets, creating a complex three-dimensional structure with anisotropical properties. Then, to define the electrical activity, two interpenetrating domains are considered, which are the intracellular and extracellular domains, representing respectively the space inside the cells and the region between them.

Quatrefoil reentry is a type of cardiac arrhythmia that consists of two adjacent figure-of-eight reentrant circuits.

Robert Plonsey was the Pfizer-Pratt University Professor Emeritus of Biomedical Engineering at Duke University. He is noted for his work on bioelectricity.

Ephaptic coupling is a form of communication within the nervous system and is distinct from direct communication systems like electrical synapses and chemical synapses. It may refer to the coupling of adjacent (touching) nerve fibers caused by the exchange of ions between the cells, or it may refer to coupling of nerve fibers as a result of local electric fields. In either case ephaptic coupling can influence the synchronization and timing of action potential firing in neurons. Myelination is thought to inhibit ephaptic interactions.

Magnetomyography

Magnetomyography (MMG) is a technique for mapping muscle activity by recording magnetic fields produced by electrical currents occurring naturally in the muscles, using arrays of SQUIDs. It has a better capability than electromyography for detecting slow or direct currents. The magnitude of the MMG signal is in the scale of pico (10−12) to femto (10−15) Tesla (T). Miniaturizing MMG offers a prospect to modernize the bulky SQUID to wearable miniaturized magnetic sensors.

Shannon Criteria

The Shannon criteria constitute an empirical rule in neural engineering that is used for evaluation of possibility of damage from electrical stimulation to nervous tissue.

Donald Choy Chang is a founding professor of the Hong Kong University of Science and Technology (HKUST). He was also the founding President of the Biophysical Society of Hong Kong. He is currently Professor Emeritus and Adjunct Professor in HKUST, and Council Member of Hong Kong Institute of Science (HKIS). Chang has wide research interest: He was an experimental physicist by training; but his publication ranges from nuclear magnetic resonance, biophysics and quantum physics.

Brian M. Salzberg is an American neuroscientist, biophysicist and professor. He is Professor of Neuroscience and of Physiology at the Perelman School of Medicine, University of Pennsylvania.

William A. Hagins

William Archer Hagins was an American medical researcher. He was chief of the Section of Membrane Biophysics in National Institute of Diabetes and Digestive and Kidney Diseases's Laboratory of Chemical Physics upon his retirement in 2007. Hagins and colleagues made the seminal discovery of the dark current in photoreceptor cells. This finding became central to understanding how the visual cells worked and led to knowledge of the importance of reattaching a detached retina as soon as possible for continued use. As a fellow of Fulbright Program, he'd also served in the United States Navy as a Research Medical Officer. He joined NIDDK's Laboratory of Physical Biology in 1958, doing independent research in the Section of Photobiology, headed by Frederick Sumner Brackett. Hagins was a mentor to many, particularly through his work with the Brackett Foundation.

References

  1. ↑ Wikswo JP Jr; Barach JP; Freeman JA (1980). "Magnetic field of a nerve impulse: First measurements". Science. 208 (4439): 53–55. Bibcode:1980Sci...208...53W. doi:10.1126/science.7361105. PMID   7361105.
  2. ↑ Swinney KR, Wikswo JP Jr (1980). "A calculation of the magnetic field of a nerve action potential". Biophysical Journal. 32 (2): 719–732. Bibcode:1980BpJ....32..719S. doi:10.1016/S0006-3495(80)85012-0. PMC   1327234 . PMID   7260298.
  3. ↑ Roth BJ, Wikswo JP Jr (1985). "The magnetic field of a single axon: A comparison of theory and experiment". Biophysical Journal. 48 (1): 93–109. Bibcode:1985BpJ....48...93R. doi:10.1016/S0006-3495(85)83763-2. PMC   1329380 . PMID   4016213.
  4. ↑ Wikswo JP Jr; Barach JP (1982). "Possible sources of new information in the magnetocardiogram". Journal of Theoretical Biology. 95 (4): 721–729. Bibcode:1982JThBi..95..721W. doi:10.1016/0022-5193(82)90350-2. PMID   7109652.
  5. ↑ Roth BJ, Wikswo JP Jr (1986). "Electrically-silent magnetic fields". Biophysical Journal. 50 (4): 739–745. Bibcode:1986BpJ....50..739R. doi:10.1016/S0006-3495(86)83513-5. PMC   1329851 . PMID   3779008.
  6. ↑ Roth BJ, Guo WQ, Wikswo JP Jr (1988). "The effects of spiral anisotropy on the electric potential and the magnetic field at the apex of the heart". Mathematical Biosciences. 88 (2): 191–221. doi:10.1016/0025-5564(88)90042-9.
  7. ↑ Bajaj AK, Kopelman HA, ((Wikswo JP Jr)), Cassidy F, Woosley RL, Roden DM (1987). "Frequency- and orientation-dependent effects of mexiletine and quinidine on conduction in the intact dog heart". Circulation. 75 (5): 1065–1073. doi: 10.1161/01.cir.75.5.1065 . PMID   2436827.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  8. ↑ Wikswo JP Jr; Altemeier W; Balser JR; Kopelman HA; Wisialowski T; Roden DM (1991). "Virtual cathode effects during stimulation of cardiac muscle: Two-dimensional in vivo measurements". Circulation Research. 68 (2): 513–530. doi: 10.1161/01.res.68.2.513 . PMID   1991354.
  9. ↑ Roth BJ, Wikswo JP Jr (1986). "A bi-domain model for the extracellular potential and magnetic field of cardiac tissue". IEEE Transactions on Biomedical Engineering. 33 (4): 467–469. doi:10.1109/TBME.1986.325804. PMID   3957401. S2CID   30462160.
  10. ↑ Sepulveda NG, Wikswo JP Jr (1987). "Electric and magnetic fields from two-dimensional anisotropic bisyncytia". Biophysical Journal. 51 (4): 557–568. Bibcode:1987BpJ....51..557S. doi:10.1016/S0006-3495(87)83381-7. PMC   1329928 . PMID   3580484.
  11. ↑ Sepulveda NG, Roth BJ, Wikswo JP Jr (1989). "Current injection into a two-dimensional anisotropic bidomain". Biophysical Journal. 55 (5): 987–999. Bibcode:1989BpJ....55..987S. doi:10.1016/S0006-3495(89)82897-8. PMC   1330535 . PMID   2720084.
  12. ↑ Roth BJ, Wikswo JP Jr (1994). "Electrical stimulation of cardiac tissue: A bidomain model with active membrane properties". IEEE Transactions on Biomedical Engineering. 41 (3): 232–240. doi:10.1109/10.284941. PMID   8045575. S2CID   12706791.
  13. ↑ Wikswo JP Jr; Lin S-F; Abbas RA (1995). "Virtual electrodes in cardiac tissue: A common mechanism for anodal and cathodal stimulation". Biophysical Journal. 69 (6): 2195–2210. Bibcode:1995BpJ....69.2195W. doi:10.1016/S0006-3495(95)80115-3. PMC   1236459 . PMID   8599628.
  14. ↑ Lin SF, Roth BJ, Wikswo JP Jr (1999). "Quatrefoil reentry in myocardium: An optical imaging study of the induction mechanism". Journal of Cardiovascular Electrophysiology. 10 (4): 574–586. doi:10.1111/j.1540-8167.1999.tb00715.x. PMID   10355700. S2CID   8440276.
  15. ↑ Staton DJ, Ma YP, Sepulveda NG, Wikswo JP (1991). "High-resolution magnetic mapping using a SQUID magnetometer array". IEEE Transactions on Magnetics. 27 (2): 3237–3240. Bibcode:1991ITM....27.3237S. doi:10.1109/20.133901.
  16. ↑ Wikswo JP Jr (1995). "SQUID magnetometers for biomagnetism and non-destructive testing: Important questions and initial answers". IEEE Transactions on Applied Superconductivity. 5 (2): 74–120. Bibcode:1995ITAS....5...74W. doi:10.1109/77.402511. S2CID   13145015.
  17. ↑ Jenks WG, Sadeghi SS, Wikswo JP Jr (1997). "SQUIDs for non-destructive evaluation". Journal of Physics D: Applied Physics. 30 (3): 293–323. Bibcode:1997JPhD...30..293J. doi:10.1088/0022-3727/30/3/002. S2CID   250886288.
  18. ↑ Roth BJ, Sepulveda NG, Wikswo JP Jr (1989). "Using a magnetometer to image a two-dimensional current distribution". Journal of Applied Physics. 65 (1): 361–372. Bibcode:1989JAP....65..361R. doi:10.1063/1.342549.
  19. ↑ Walker GM, Sai JG, Richmond A, Chung CY, Stremler MA, Wikswo JP (2005). "Effects of flow and diffusion on chemotaxis studies in a microfabricated gradient generator". Lab on a Chip. 5 (6): 611–618. doi:10.1039/b417245k. PMC   2665276 . PMID   15915253.
  20. ↑ "Executive Profile: John P. Wikswo Ph.D.", Bloomberg Businessweek, accessed 2014-01-21.

Further reading

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.