Harry Pennes, Biological Physicist

First page of Pennes (1948) J Appl Physiol 1:93–122.

I admire scientists who straddle the divide between physics and physiology, and who are comfortable with both mathematics and medicine. In particular, I am interested in how such interdisciplinary scientists are trained. Many, like myself, are educated in physics and subsequently shift focus to biology. But more remarkable are those (such as Helmholtz and Einthoven) who begin in biology and later contribute to physics.

Obituary of Harry H. Pennes.

Which brings me to Harry Pennes. Below I reproduce his obituary published in the April 1964 issue of the American Journal of Psychiatry (Volume 120, Page 1030).

First page of Wissler (1998).

Before we discuss what’s in his obituary, consider what’s not in it: physics, mathematics, or engineering. Yet, today Pennes is remembered primarily for his landmark contribution to biological physics: the bioheat equation. Russ Hobbie and I analyze this equation in Section 14.11 of Intermediate Physics for Medicine and Biology. In an article titled “Pennes’ 1948 Paper Revisited” (Journal of Applied Physiology, Volume 85, Pages 35–41, 1998), Eugene Wissler wrote:

So, how did a psychiatrist make a fundamental contribution to physics? I don’t know. Indeed, I have many questions about this fascinating man.

  1. Did he work together with a mathematician? No. Pennes was the sole author on the paper. There was no acknowledgment thanking a physicist friend or an engineer buddy. The evidence suggests the work was done by Pennes alone.
  2. Did he merely apply an existing model? No. He was the first to include a term in the heat equation to account for convection by flowing blood. He cited a previous study by Gagge et al., but their model was far simpler than his. He didn’t just adopt an existing equation, but rather developed a new and powerful mathematical model.
  3. Was the mathematics elementary? No. He solved the heat equation in cylindrical coordinates. The solution of this partial differential equation included Bessel functions with imaginary arguments (aka modified Bessel functions). He didn’t cite a reference about these functions, but introduced them as if they were obvious.
  4. Was his paper entirely theoretical? No. The paper was primarily experimental and the math appeared late in the article when interpreting the results.
  5. Were the experiments easy? No. In fact, they were a little gross. They required threading thermocouples through the arm with no anesthesia. Pennes claimed the “phlegmatic subjects occasionally reported no unusual pain.” I wonder what the nonplegmatic subjects reported?
  6. Was Pennes’ undergraduate degree in physics? I don’t know.
  7. Did Pennes’ interest in math arise late in his career? No. His famous 1948 paper was submitted a few weeks before his 30th birthday.
  8. Did Pennes work at an institution out of the mainstream that might promote unusual or quirky career paths? No. Pennes worked at Columbia University’s College of Physicians and Surgeons, one of the oldest and most respected medical schools in the country.
  9. Did Pennes pick up new skills while in the military? Probably not. He was 23 years old when the Japanese attacked Pearl Harbor, but I can’t find any evidence he served in the military during World War II. He earned his medical degree in 1942 and arrived at Columbia in 1944.
  10. Do other papers published by Pennes suggest an expertise in math? I doubt it. I haven’t read them all, but most study how drugs affect the brain. In fact, his derivation of the bioheat equation seems so out-of-place that I’ve entertained the notion there were two researchers named Harry H. Pennes at Columbia University.
  11. Did Pennes’ subsequent career take advantage of his math skills? Again, I am not sure but my guess is no. The Columbia-Greystone Brain Project is famous for demonstrating that lobotomies are not an effective treatment of brain disorders. Research on chemical warfare should require expertise in toxicology.
  12. How did Pennes die? According to Wikipedia he committed suicide. What a tragic loss of a still-young scientist!

I fear my analysis of Harry Pennes provides little insight into how biologists or medical doctors can contribute to physics, mathematics, or engineering. If you know more about Pennes’ life and career, please contact me (roth@oakland.edu).

Even though Harry Pennes’ legacy is the bioheat equation, my guess is that he would’ve been shocked that we now think of him as a Biological Physicist.

Originally published at hobbieroth.blogspot.com on February 1, 2019.

Professor of Physics at Oakland University and coauthor of the textbook Intermediate Physics for Medicine and Biology.