Gas station without pumps

2012 August 19

Medical Instrumentation, Chapters 9–14

As I mentioned in Medical Instrumentation, first 5 chapters, Medical Instrumentation, Chapter 6,  and Medical Instrumentation, Chapters 7 and 8, I’ve been slogging through one of the potential text books for the circuits course: Medical Instrumentation: Application and Design, 4th Edition. John G. Webster. Publisher: Wiley, 2009. # ISBN-10: 0471676004; # ISBN-13: 978-0471676003.  Here are my notes on the rest of the book (I plan to return it tomorrow to the library).

Chapter 9

Frank P. Primiano, Jr.

I only skimmed chapter 9, as there did not seem to be much of use for the circuits course.

Richard had suggested making a rotating-vane flowmeter using a toy siren-whistle as the turbine and a photodetector to determine its speed.  I investigated that possibility, but the siren whistles have very low drag on their turbines and continue to spin for a couple of seconds after the air flow has stopped.  One might be able to use that for a wind-speed indicator, but the response time is far too slow for measuring air flow due to breathing.

The section on measuring gas concentrations is intellectually interesting and may be of some value to bioengineers, but doesn’t seem relevant for the circuits course.

Chapter 10

Robert A. Peura

It’s nice to know how a pH probe works and how blood gases are measured, but I don’t see a lot we can do in the circuits class.
The plot of the absorptivities of carboxyhemoglobin, oxyhemoglobin, reduced hemoglobin, and methmoglobin in Figure 10.6 are interesting, and are needed for explaining how a pulse oximeter works, as well as why 940nm LEDs should be a good choice for detecting arterial blood pulses, since reduced hemoglobin has about 3/5th the extinction coefficient of oxyhemoglobin there.  An even longer wavelength (say 1000nm) would be even better, since the ratio drops to about 1/4, if LEDs and phototransistors for that wavelength were readily available, but 950nm is about as long a wavelength LED as is available.

I considered doing a pulse-oximetry lab, but the difficulty of calibrating the device made it seem pointless.  That’s too bad in a way, as the technique relies inherently on considering the AC rather than the DC component of the signal.

Chapter 11

Lawrence A. Wheeler

Nothing in this chapter seems relevant to the circuits class.  I had at one point considered doing a very early lab in which electric fields were illustrated by measuring voltages at different points in an electrophoresis gel, but that didn’t seem worth the messy setup.  Most of the bioengineers will do gel electrophoresis in other labs anyway.

Chapter 12

Melvin P. Siedband

Nothing in the imaging chapter seems relevant for the circuits class.

Chapter 13

Michael R. Neuman

It doesn’t look like there is anything in Chapter 13 for our course.

Chapter 14

ELECTRICAL SAFETY                               638
Walter H. Olson

14.1       Physiological Effects of Electricity   639

Useful figure and definitions of different levels of shock hazard.

14.2       Important Susceptibility Parameters   641

Perhaps a bit too much information for students to process about current needed for hazard.

14.3       Distribution of Electric Power   646

Fairly straightforward description of electric distribution in buildings.  Students should know this already, but most likely don’t.

14.4       Macroshock Hazards   650

Somewhat wordy description of hazards, repeating previous sections.

14.5       Microshock Hazards   653

Important for those who are making direct electrical connections to the heart, which we are NOT.

14.6       Electrical-Safety Codes and Standards   658

As boring as the title makes it sound.

14.7       Basic Approaches to Protection Against Shock   659

Short and nearly contentless.

14.8       Protection: Power Distribution   660

Good description of GFCIs, but the schematic in Figure 14.15 is not explained, and how it works is not obvious.

14.9       Protection: Equipment Design   663

Reasonable description of double insulation and isolation barriers.  Doesn’t seem to indicate that optical couplers are now the dominant method (though I believe they are) for information transfer across the isolation barrier—they give it only as one of three possible options.

14.10     Electrical-Safety Analyzers   667

One paragraph, not much content.

14.11     Testing the Electric System   667

Doesn’t really say how to do it, just that the usual 3-LED tester used by construction workers and home electricians is inadequate.

14.12     Tests of Electric Appliances   669

Basically repeats material from the National Fire Protection Association standards (NFPA99-2005).

Problems   673
References   674

Chapter 14 has some good material on electrical safety, but is probably too much information for the circuits course.  I’m going to have to find a more concise description that students will actually read and remember.

Bottom line

There are bits and pieces of Medical Instrumentation that could be useful to our students, but not enough of the content is relevant to the course to use it as a text and the parts that are relevant are too long for the book to be useful as a reserve book in the library.  It was probably worth my time to read (most of) the book, but I doubt that it will be worthwhile for the students.

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