Friday, July 26, 2019

The Oxford English Dictionary

The Meaning of Everything: The Story of the Oxford English Dictionary, by Simon Winchester, superimposed on Intermediate Physics for Medicine and Biology.
The Meaning of Everything,
by Simon Winchester.
I’m a fan of Simon Winchester, and I recently finished his book The Meaning of Everything: The Story of the Oxford English Dictionary. I enjoyed it immensely, and it motivated me to spend a morning browsing through the OED in the Oakland University library, which owns the 1989 twenty-volume second edition.

Rather than describe a typical OED entry, I’ll show ten examples using words drawn from Intermediate Physics for Medicine and Biology.


The entry for bremsstrahlung in the Oxford English Dictionary.

In OED entries, the information right after the word in parentheses is the pronunciation based on the International Phonetic Alphabet, and the text within brackets is the etymology. Bremsstrahlung is German (G.; the OED uses lots of abbreviations). It has its own OED entry, so I guess it’s considered part of the English language too. The entry spans two columns, so I had to cut and paste photos of it. To my ear, bremsstrahlung is the oddest sounding word in IPMB.


The entry for candela in the Oxford English Dictionary.

The origin of candela is from Latin (L.). IPMB and Wikipedia define the candela as lumen per steradian. I don’t see the solid angle connection listed in the OED.


The entry for chronaxie in the Oxford English Dictionary.

Russ Hobbie and I spell chronaxie ending in -ie, which is the most common spelling, although some end it in -y. Chronaxie is from a French (F.) term that appeared in an 1909 article by Louis Lapicque, cited in IPMB.


The entry for cyclotron in the Oxford English Dictionary.

My favorite part of an OED entry are the quotations illustrating usage. Several quotes are provided for cyclotron. The first is from a 1935 Physical Review article by Ernest Lawrence, the cyclotron’s inventor. XLVIII is the volume number in Roman numerals, and 495/2 means the quote can be found on page 495, column 2.


The entry for defibrillation in the Oxford English Dictionary.

Two definitions of defibrillation exist. IPMB uses the word in the second sense: the stopping of fibrillation of the heart. Other forms of this medical (Med.) term are listed, with defibrillating being the participial adjective (ppl. a.) and defibrillator the noun. Carl Wiggers is a giant in cardiac electrophysiology, and the Lancet is one of the world’s leading medical journals.


The OED’s definition of electrotonus is different from mine.

The entry for electrotonus in the Oxford English Dictionary.

In IPMB, Russ and I write
The simplest membrane model is one that obeys Ohm’s law. This approximation is valid if the voltage changes are small enough so the membrane conductance does not change, or if something is done to inactivate the normal changes of membrane conductance with voltage. It is also useful for myelinated nerves between the nodes of Ranvier. This is called electrotonus or passive spread.
IPMB says nothing about a constant current stimulus, and the OED says nothing about passive spread. I wonder if I’ve been using the word correctly? Wikipedia agrees with me.

The two vertical lines in the top left corner on the entry indicate an alien word (used in English, but from another language). I would have thought bremsstrahlung more deserving of this designation than electrotonus.


The entry for fluoroscope in the Oxford English Dictionary.

Wilhelm Röntgen discovered x-rays in late 1895, so I’m surprised to see the term fluoroscope used only one year later. X-rays caught on fast. Nature is one of the best-known scientific journals.


My PhD advisor John Wikswo and I are engaged in a quixotic attempt to introduce a new unit, the leibniz.

The entry for leibniz in the Oxford English Dictionary.

If I were going to append a new definition, it would look something like this:
2. A unit corresponding to a mole of differential equations. 2006 HUANG et al. Rev. Physiol. Biochem. Pharmacol. CLVII. 98 Avogadro’s number of differential equations may be defined as one Leibnitz. 2006 WIKSWO et al. IEE P-Nanobiotechnol. CLIII. 84 It is conceivable that the ultimate models for systems biology might require a mole of differential equations (called a Leibnitz). 2015 HOBBIE and ROTH Intermediate Physics for Medicine and Biology 53 In computational biology, a mole of differential equations is sometimes called a leibniz.


The entry for quatrefoil in the Oxford English Dictionary.

Wikswo coined the term quatrefoil for four-fold symmetric reentry in cardiac tissue. Quatrefoil appears in the OED, but its definition is focused on foliage rather than heart arrhythmias. I guess Wikswo didn’t invent the word but he did propose a new meaning. I can’t complain that this sense of the word is missing from the OED, because quatrefoil reentry wasn’t discovered until after the second edition went to press. My proposed addition is:
3. A four-fold symmetric cardiac arrhythmia. 1999 LIN et al. J. Cardiovasc. Electrophysiol. X. 574 A novel quatrefoil-shaped reentry pattern consisting of two pairs of opposing rotors was created by delivering long stimuli during the vulnerable phase.


The entry for tomography in the Oxford English Dictionary.

Godfrey Hounsfield built the first computed tomography machine in 1971. I didn’t realize that tomography had such a rich history before then. I don’t like the OED’s definition of tomography. I prefer something closer to IPMB’s: “reconstructing, for fixed z, a map of some function f(x,y) from a set of projections F(θ,x').”

Missing Words

Some words from IPMB are not in the OED; for example chemostat, electroporation, and magnetosome. Kerma is absent, but it’s an acronym and they aren’t included. Brachytherapy is absent, even from the long entry for the prefix brachy-. Sphygmomanometer doesn’t have its own entry, although it’s listed among the surprisingly large number of words starting with the prefix sphygmo-. Magnetocardiogram is included under the prefix magneto-, but the more important magnetoencephalogram is not. I was hoping to find the definition of bidomain, but alas it’s not there. Here’s my version.
bidomain (ˌbaɪdəʊ'meɪn). Phys. [f. BI- + -DOMAIN.] A mathematical description of the electrical behavior of syncytial tissue such as cardiac muscle. 1978 TUNG A Bi-domain Model for Describing Ischemic Myocardial D-C Potentials (Dissertation) 2 Bi-domain, volume-conductive structures differ from classical volume conductors (mono-domain structures) in that a distinction is made between current flow in the extracellular space and current flow in the intracellular space. 1983 GESELOWITZ and MILLER Ann. Biomed. Eng. XI. 200  The equations of the bidomain model are a three-dimensional version of the cable equations.

The OED took decades to complete, mostly during the Victorian era. The effort was led by James Murray, the hero of Winchester’s book. He supervised a small group of assistants, plus a motley crew of contributors whose job was to search English literature for examples of word use. Winchester’s stories about this collection of oddballs and misfits is engrossing; they volunteered countless hours with little recognition, some contributing tens of thousands of quotations, each submitted on a slip of paper during those years before computers. I can think of only one modern parallel: those unsung heroes who labor over Wikipedia.

The Professor and the Madman: A Tale of Murder, Insanity, and the Making of the Oxford English Dictionary, by Simon Winchester, superimposed on Intermediate Physics for Medicine and Biology.
The Professor and the Madman,
by Simon Winchester.
If you like The Meaning of Everything, you’ll love Winchester’s The Professor and the Madman, also about the Oxford English Dictionary. In addition, Winchester has written several fine books about geology; my favorites are Krakatoa and The Map That Changed the World.

To close, I’ll quote the final paragraph of a speech that Prime Minister Stanley Baldwin gave in 1928 at a dinner celebrating the completion of the OED, which appears at the end of Winchester's Prologue to The Meaning of Everything.
It is in that grand spirit of devotion to our language as the great and noble instrument of our national life and literature that the editors and the staff of the Oxford Dictionary have laboured. They have laboured so well that, so far from lowering the standard with which the work began, they have sought to raise it as the work advanced. They have given us of their best. There can be no worldly recompense—expect that every man and woman in this country whose gratitude and respect is worth having, will rise up and call you blessed for this great work. The Oxford English Dictionary is the greatest enterprise of its kind in history.
Intermediate Physics for Medicine and Biology nestled among volumes of the Oxford English Dictionary.
Intermediate Physics for Medicine and Biology
nestled among volumes of the Oxford English Dictionary.

Friday, July 19, 2019

The 5G Health Hazard That Isn’t

Screenshot of the start of the article "The 5G Health Hazard That Isn't" by William Broad in the New York Times.
Screenshot of the start of the article
"The 5G Health Hazard That Isn’t"
by William Broad in the New York Times.
A recent article by William Broad in the New York Timestitled “The 5G Health Hazard That Isn’ttells the sad story of how unfounded fears of radio-frequency radiation were stoked by one mistaken scientist. Broad begins
In 2000, the Broward County Public Schools in Florida received an alarming report. Like many affluent school districts at the time, Broward was considering laptops and wireless networks for its classrooms and 250,000 students. Were there any health risks to worry about?
The district asked Bill P. Curry, a consultant and physicist, to study the matter. The technology, he reported back, was “likely to be a serious health hazard.” He summarized his most troubling evidence in a large graph labeled “Microwave Absorption in Brain Tissue (Grey Matter).”
The chart showed the dose of radiation received by the brain as rising from left to right, with the increasing frequency of the wireless signal. The slope was gentle at first, but when the line reached the wireless frequencies associated with computer networking, it shot straight up, indicating a dangerous level of exposure.

“This graph shows why I am concerned,” Dr. Curry wrote. The body of his report detailed how the radio waves could sow brain cancer, a terrifying disease that kills most of its victims.
Over the years, Dr. Curry’s warning spread far, resonating with educators, consumers and entire cities as the frequencies of cellphones, cell towers and wireless local networks rose. To no small degree, the blossoming anxiety over the professed health risks of 5G technology can be traced to a single scientist and a single chart.
Except that Dr. Curry and his graph got it wrong.
Russ Hobbie and I describe the possible effects of weak electric and magnetic fields in Section 9.10 of Intermediate Physics for Medicine and Biology. We quote a review by Moulder et al. (2005) that concludes
Overall, a weight-of-evidence evaluation shows that the current evidence for a causal association between cancer and exposure to RF [radio frequency] energy is weak and unconvincing.
In his New York Times article, Broad goes on to describe how your “skin” blocks the radio waves. That’s not how I would say it. The waves can’t penetrate your body because of “skin depth” (to learn more about skin depth, do Problem 29 in Chapter 8 of IPMB). An electromagnetic wave penetrates a conductor to a distance on the order of the skin depth, which decreases as the frequency increases. A typical 5G frequency is 3 GHz, corresponding to a skin depth of about 30 mm (a little over an inch). Therefore, deep structures in your body are somewhat shielded from this radiation. It has nothing to do with skin itself; the effect works the same when the wave tries to penetrate the surface of the ocean. It depends on the electrical conductivity. Some planned 5G networks will operate at even higher frequencies (up to 300 GHz). In that case, the skin depth would be ten times smaller than for 3 GHz, or 3 mm, similar to the thickness of skin.

If the amplitude of the electromagnetic wave was high enough, it could burn you. Most people who object to radio frequency waves aren’t worried about heating. They’re concerned about hypothetical nonthermal effects, like causing cancer.

I can think of many reasons to ditch your fancy-schmancy 5G cell phone. Cancer isn’t one of them.

Friday, July 12, 2019

The Fifth Solvay Conference

Participants at the Fifth Solvay Conference in 1927.
Participants at the Fifth Solvay Conference in 1927.
This iconic photograph taken at the Fifth Solvay Conference shows the greatest gathering of intelligence ever. Physicists met in October 1927 in Brussels to discuss the then-new theory of quantum mechanics. Russ Hobbie and I mention several of the conference participants in Intermediate Physics for Medicine and Biology.
Niels Bohr
Niels Bohr (Copenhagen, Denmark). The Bohr model of the hydrogen atom and its energy levels is dealt with in Chapter 14 about Atoms and Light, and Bohr’s work on stopping power—how a charged particle loses energy as it passes through tissue—is discussed in Chapter 15 about the Interaction of Photons and Charged Particles with Matter.
Max Born
Max Born (Göttingen, Germany). The Born charging energy appears in Chapter 6 about Impulses in Nerve and Muscle Cells.
William Lawrence Bragg
William Lawrence Bragg (Manchester, England). Chapter 16 about the Medical Uses of X-Rays contains the Bragg-Gray relationship, specifying the absorbed dose in a cavity. The Bragg peak was discovered by Lawrence's father William Henry Bragg (invited to the conference but could not attend).
Arthur Compton
Arthur Compton (Chicago, United States). Compton scattering—the dominant mechanism by which x-rays interact with electrons in tissue at energies around 1 MeV—plays a central roll in Chapter 15. Compton’s name is associated with the Compton wavelength and the Compton cross section.
Marie Curie
Marie Curie (Paris, France). The curie—a unit of radioactivity equal to 37,000,000,000 decays per second—appears in Chapter 17 about Nuclear Physics and Nuclear Medicine. The Curie temperature, discussed in Chapter 8 on Biomagnetism, is named after Marie Curie’s husband Pierre Curie, who died two decades before the Fifth Solvay conference.
Louis de Broglie
Louis de Broglie (Paris, France). de Broglie and his discovery, the relationship between an electron’s momentum and wavelength, is considered when discussing the electron microscope in Chapter 14.
Peter Debye
Peter Debye (Leipzig, Germany). Debye appears in IPMB three times: The debye unit for dipole moment is discussed in Chapter 6, and the Debye length and the Debye-Huckel model are analyzed in Chapter 9 about Electricity and Magnetism at the Cellular Level.
Paul Dirac
Paul Dirac (Cambridge, England). Dirac is most famous for contributing to quantum mechanics, but he is remembered also for the Dirac delta function, which is developed in Chapter 11 about the Method of Least Squares and Signal Analysis.
Albert Einstein
Albert Einstein (Berlin, Germany). The Einstein relationship between diffusion and viscosity is studied in Chapter 4 about Transport in an Infinite Medium, and the unit of the einstein—a mole of photons—appears in Chapter 14. Throughout IPMB, we use Einstein’s ideas about the special theory of relativity and the quantum theory of light, although we rarely mention him by name.
Paul Langevin
Paul Langevin (Paris, France). The Langevin equation is used in Chapter 4 to model the random motion of a particle in a viscous liquid.
Hendrik Lorentz
Hendrik Lorentz (Haarlem, the Netherlands). The Lorentz force exerted on a charge by electric and magnetic fields is a central concept in Chapter 8.
Wolfgang Pauli
Wolfgang Pauli (Hamburg, Germany). The Pauli exclusion principle—no two electrons in an atom can have the same values for all their quantum numbers—is introduced in Chapter 14.
Max Planck
Max Planck (Berlin, Germany). The Nernst-Planck equation is introduced in Chapter 9, Planck’s blackbody radiation formula is analyzed in Chapter 14, and Planck’s constant appears throughout IPMB.
Erwin Schrodinger
Erwin Schrodinger (Zurich, Switzerland). The Schrodinger equation is mentioned in passing at the start of Chapter 3 about Systems of Many Particles.

Watch this fascinating movie taken at the conference.

The Fifth Solvay Conference, 1927.

The greatest physicist of the early 20th century who did not attend the Fifth Solvay Conference was Ernest Rutherford, whose gold foil experiment proved that the atom contains a massive nucleus. Rutherford—who is my academic great-great-great-great-grandfather—was at the Seventh Solvay Conference in 1933 (see photograph below; Rutherford is sitting, sixth form the right), which is probably the second greatest gathering of intelligence ever (Einstein did not attend).

Participants at the Seventh Solvay Conference, 1933.
Participants at the Seventh Solvay Conference, 1933.
One little known fact about the Fifth Solvay Conference is that several of the participants brought their copy of Intermediate Physics for Medicine and Biology.

Participants at the Fifth Solvay Conference, holding copies of Intermediate Physics for Medicine and Biology.

Friday, July 5, 2019

The Biophysics and Pathophysiology of Lesion Formation During Radiofrequency Catheter Ablation

This week I went with a group of Oakland University undergraduates—part of an American Heart Association-funded summer research program—to Beaumont Hospital in Royal Oak, Michigan to visit Dr. David Haines. Haines is the director of the Heart Rhythm Center, and an expert in using radiofrequency catheter ablation to treat cardiac arrhythmias such as atrial fibrillation.

During the visit, I noticed how physics underlies most of Haines’s work in the clinic. Much of this physics is described in Intermediate Physics for Medicine and Biology. Russ Hobbie and I discuss the electrical behavior of the heart and the electrocardiogram in Chapter 7, arrhythmias such as fibrillation in Chapter 10, and the bioheat equation governing the tissue temperature in Chapter 14.

Cardiac Electrophysiology: From Cell to Bedside, 4th Ed., Edited by Zipes and Jalife, superimposed on Intermediate Physics for Medicine and Biology.
Cardiac Electrophysiology:
From Cell to Bedside
, 4th Ed.,
Edited by Zipes and Jalife.
Haines wrote a chapter about “The Biophysics and Pathophysiology of Lesion Formation during Radiofrequency Catheter Ablation” that appeared in Cardiac Electrophysiology: From Cell to Bedside, a book often cited in IPMB. He begins
The rationale of ablation is that, for every arrhythmia, there is a critical region of abnormal impulse generation or propagation that is required for that arrhythmia to be sustained clinically. If that substrate is irreversibly altered or destroyed, then the arrhythmia should not occur spontaneously or with provocation. To accomplish this with a catheter, several criteria must be met. The technology needs to be controllable: Big enough to incorporate the target but small enough to minimize collateral damage. It needs to be affordable and adaptable to equipment conventionally found in the electrophysiology (EP) suite. Despite considerable experience and experimentation with a variety of catheter ablation technologies, ablation with radiofrequency (RF) electrical energy emerged and has persisted as the favored modality. The study of the mechanisms of RF energy heating and the tissue’s response to this injury will give insight into these and other phenomena and should allow the operator to optimize procedure outcome.
Let me describe some of the physics of catheter ablation.
  • The Catheter. A catheter is used to place the lead used for ablation into the heart. Usually it’s inserted into a vein in the leg, and then snaked through the vessels into the right atrium. (Ablating tissue in the left atrium is trickier; you may have to create a small hole between the atria by doing a transseptal puncture.) Catheterization is less invasive than open heart surgery, so some patients can avoid even a single night in the hospital after treatment.
  • Radiofrequency Energy. Ablation is performed using electrical energy with a frequency between 0.3 and 1 MHz (in the frequency band of AM radio). These frequencies are too high to cause direct electrical stimulation of muscles or nerves. The mechanism of ablation is Joule heating, like in your toaster, which raises the temperature of the tissue within a few millimeters of the lead tip.
  • Lesion Formation. Cells become irreversibly damaged at temperatures on the order of 50° C. The temperature of the lead tip is kept below 100° C to avoid boiling the plasma and coagulating proteins.
  • Atrial Fibrillation. Atrial fibrillation is the most common arrhythmia treated with ablation. Fibrillation means that the electrical wave fronts propagate in a irregular and chaotic way, so the mechanical contraction is unorganized and ineffective. Unlike ventricular fibrillation, which is lethal in minutes if not defibrillated, a person can live with atrial fibrillation, but the heart won’t pump efficiently causing fatigue, the backup of fluid into the lungs, and an increased risk of stroke.
  • Electrical Mapping. The first part of the clinical procedure is to map the arrhythmia. Multiple electrodes on the catheter record the electrocardiogram throughout the atrium, locating the reentrant pathway or the focus (an isolated spot that initiates a wave front). If the arrhythmia is intermittent, then it may need to be triggered by electrical stimulation in order to map it.
  • Ablation Sites. Once the arrhythmia is mapped, the doctor can determine where to ablate the tissue. Usually many isolated spots will be ablated to create a large lesion, often located around the pulmonary veins where many reentrant pathways occur.
While visiting Beaumont, the students and I talked with Haines about his career, and watched him perform a procedure. The team of specialists and their high-tech equipment were impressive; an example of physics and engineering intersecting physiology and medicine.

Cardiac Electrophysiology: From Cell to Bedside alongside Intermediate Physics for Medicine and Biology.
My copy of Cardiac Electrophysiology:
From Cell to Bedside
, alongside IPMB.
I’ll end by quoting Haine’s chapter summary in Cardiac Electrophysiology: From Cell to Bedside.
During RF catheter ablation, RF current passes through the tissue in close contact with the electrode and is resistively heated. The temperature of the tissue at the border of the lesion is reproducible in the 50°C to 55°C range. It is likely that the dominant model of myocardial injury is thermal, although electrical fields have been demonstrated to stun and kill cells depending on the field intensity. On inspection of the myocardial lesions, the tissue shows evidence of desiccation, inflammation, and microvascular injury, which certainly leads to ischemia. Late injury or recovery of the tissue at the lesion border zone may occur as a result of progression or resolution of inflammatory response or endothelial injury. On the cellular level, many possible mechanisms of myocyte damage exist, but membrane injury probably dominates. This may lead to cellular depolarization, intracellular Ca2+ overload, and cell death. Further damage to the cytoskeleton, cellular metabolism, and nucleus may occur at lower temperatures with more prolonged hyperthermia exposure. RF catheter ablation has been proven to be an effective clinical modality for the treatment of arrhythmias, but many of the basic pathophysiologic effects of this empirical procedure on the tissue and cellular level remain to be determined.

Dr. David Haines of Beaumont Hospital.

An interview with Dr. David Haines to discuss radiofrequency ablation.