Interview with John Webster

Featured Engineer

John Webster

John Webster - Biomedical Engineering, University of Wisconsin- Madison

Image Note: The hot flash monitor is worn on the sternum and for a week measures electric conductivity of the skin, which goes up with sweating.

How did you get into electronics/ engineering and when did you start?

In 1947 when I was in 10th grade I decided to be a physicist. Then a neighbor was cleaning out his garage and said, “Hey kid, you want this box of parts?” I found a bunch of transformers and spent the summer in our basement building arc welders, etc. and decided to be an electrical engineer.

When I was about 30 I read an article in the Proceedings of the IRE that NIH was looking for experienced engineers to earn a PhD in this new field of Biomedical Engineering to become teachers and would pay all the bills. So I turned to my wife who was large with our 4th child and said, “How would you like to go back to school?” She agreed, I earned my PhD, and have been a teacher and researcher in medical devices for the last 44 years.

What are your favorite hardware tools that you use?

Instrumentation amplifier chip. I use the Linear Technology LT1920. It is great for amplifying the 1 mV electrocardiogram and rejecting power-line interference.

What are your favorite software tools that you use?

Word

What is on your bookshelf?

Medical instrumentation: application and design, 4th edition, John Wiley & Sons, 2010. Applied bioelectricity from electrical stimulation to electropathology, Springer, 1998.

What has been your favorite project?

I have been answering the question, “What is the probability that Tasers can electrocute the heart?” People don’t volunteer as subjects so we used pigs. We inserted the Taser dart closer and closer to the heart to learn the distance from the Taser dart to the heart that would cause ventricular fibrillation and cardiac arrest. But humans are all different body sizes, so we used echocardiography to measure human distances from the skin to the heart. But all Taser darts don’t land over the heart. So we used police reports on where Taser darts land. But the electric current spreads out within the body. So we used finite element computer modeling with all of the above to estimate the probability that a Taser could electrocute the heart. It is rare, about 6 in a million, but better than the alternative, which is frequently a police bullet.

In performing your finite element analysis do you write your own algorithm/software. What software do you use? (matlab, etc)

Divide the regions of interest into small “elements”

Partial differential equations to algebraic equations
2-D (triangular elements, quadrilateral elements, etc.)
3-D (tetrahedral elements, hexahedral elements, etc.)
Nonuniform mesh is allowed
Software & Hardware
PATRAN 7.0 (MacNeal-Schwendler, Los Angeles )
ABAQUS 5.8 (Hibbitt, Karlsson & Sorensen, Inc., Farmington Hills, MI)
HP C-180, 1152 MB of RAM, 34 GB Storage

Do you have any note-worthy engineering experiences?

I learned instrumentation while measuring pressures, temperatures, and flows in rockets. The rockets were the size of a man. We remotely measured flow of fuel into the rocket chamber, pressures in the rocket chamber, temperatures in the wall of the rocket, but they frequently blew up so you had to stand about 200 m away.

Later I decided to measure pressures, temperatures, and flows in the body. But you can’t put sensors in the lung or in the heart, so it is very interesting to learn how to measure these variables indirectly. We are developing an permanently implantable brain pressure sensor in which a silicon diaphragm with a coil on it moves closer to a second coil when the pressure increases. An external reader measures the change in resonant frequency.

What are you currently working on?

About 1 in 500 babies has hydrocephalus, where the brain does not drain properly, brain pressure builds up, and a shunt drain must be installed. About 40% of shunts eventually block with debris, and the pressure damages the patient. We are working on a miniature pressure sensor to be permanently implanted in the skull that could be interrogated by an external reader using electromagnetic coupling. Other have used this principle. Our coil will be 3 mm in diameter. We will test it in sheep for years to ensure biocompatibility and reliability.

What direction do you see your business heading in the next few years?

Many physicians have problems they would like solved by engineers. I find it better to ask them what problems they think engineers might solve rather than trying to invent applications for our engineering tools.

What challenges do you foresee in our industry?

If we invent a new medical device, it takes large funds and years of waiting to get the Food and Drug Administration (FDA) to approve its use. Meanwhile your small company goes bankrupt.