I was surprised at my recent physical, to find that height and weight were to be measured with or without clothing.
Of course, there are always errors in things, and many medical measurements serve as indicators rather than exact data.
But one's height may surely be an inch or more different with or without shoes? As regards weight, out of curiosity I measured my clothing at home, dumping what I had worn at the clinic onto the bathroom floor, and I found that I was 150 lbs dressed, but only 144 naked.
Warming up to my home experimentation I took my temperature at different parts of the body. We've all seen on TV the infra-red gun aimed at the foreheads of Ebola-suspected passengers at airports (which itself opens a Pandora's box of questions), but I used just the standard little gizmo I had on the bathroom shelf with an LCD readout and button battery. I found armpit to be 94.8F, mouth 94.0, hand 93.8, and groin 92.3F -- very disturbing, in consideration of the more commonly quoted "98.something", and so I put in a new battery. The readings are still more than 2 degrees below normal, so I must be some sort of a cold fish...
A medical measurement that always intrigues me is that of blood pressure. Should the cuff around the upper arm be with or without shirt and sweater -- and should readings be different sitting down or standing up? And will it the same if repeated within a few minutes?
At my physical I also experienced a bone density test. Density is just mass divided by volume, but I mused that it would be somewhat impractical for me to cut out a chunk of bone, measure its volume with vernier calipers, and its weight (not forgetting to divide by "g").
As I sat there I was reminded of a specimen of platinum that I had bought from a jeweller during the 13% inflation of 1979. Driving home with my (then) $400 one-ounce slab of this more-valuable-than-gold element I remember I began to develop neurotic thoughts. At work I had run, not walked, to the lab and made a careful measurement of mass and dimensions. Fortunately, the density came out to be precisely the value for platinum as given by our Handbook of Chemistry and Physics.
What they commonly do these days for bone density is send sound waves through your heel bone, or, in a different test, X-rays. In principle you sit down and put your feet on an apparatus and either X-rays or sound waves are sent through the bone -- I didn't know which had happened to me, altho' I suspected sound waves. Further, I've found that asking personnel about the instrumentation, a la Sheldon, may not always be appreciated. However, I read [red] that the amount an ultrasound beam is absorbed is then compared with the amount absorbed by a typical 30 year old male bone. (Why the male is chosen as a standard I'm not sure.) The beam is of a fixed cross-section, and the length of bone is a given. As regards X-rays, good, healthy, dense bone absorbs X-rays, they say; so if you don't get much absorption your bones are deemed too lightweight and you may be tending towards osteoporosis.
For the sound waves method (actually ultrasound, where the waves are of a higher frequency than a dog can hear) a similar thing happens -- the amount of absorption is measured, compared to that for that standard healthy 30 yr old male bone.
Another interesting medical test concerns blood flow to the brain, via our carotid arteries -- one on each side of the neck. Using a stethoscope a doctor can say whether there is possible plaque build-up, because such flow tends to be turbulent, with an associated swirling, rushing noise. Less subjective would be the 'ultrasound Doppler', where sound waves are aimed as carefully as possible at the artery, and are reflected off the moving blood cells, yielding both speed of the blood (like a policeman's Doppler radar) and a rather unclear picture of the flow plus any partial blockage.
In general, better pictures of everything inside the body are given by the beautifully sophisticated MRI -- no X-radiation, just radio and a strong magnetic field, both of which we (so far) believe to be harmless.
Finally, after that physical I realized that, were I young again, I'd be strongly tempted to go into the whole fascinating field of medical measurements.
Dr. David Nightingale is Professor Emeritus of Physics at the State University of New York at New Paltz, and is the co-author of the text, A Short Course in General Relativity.
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