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A Magnetometer study on the effect of Smoking
Sensitive electronic magnetometers have many uses. They are of course indispensable aboard satellites, and on airplanes mapping the local structure of the Earth's field, e.g. when searching for oil. Airport gates use them for the detection of firearms, while stores and libraries tag their materials magnetically and use such gates to prevent anauthorized removal. The navy uses them to detect submarines under water, and they help surveyors locate boundary stakes buried in the ground or hidden by vegetation.
Perhaps the most striking use of such an instrument was in the medical experiments of Dr. David Cohen at the Massachussetts Institute of Technology (MIT). Cohen's lab was lined with screening coils whose current canceled most of the outside geomagnetic field. Inside the lab he built a small room which shielded out any remaining magnetic influence. It had five sets of walls nested one inside the other, like Russian matrioshka dolls, separated by alternate layers of iron (to keep out constant magnetic fields) and aluminum (to shield against electromagnetic fluctuations).
No detectable magnetic field reached the interior of the room, and some extremely sensitive magnetic observations could be conducted there. Cohen experimented there with magnetic signals from the heart and the brain, but his most intriguing result, published in 1979, concerned the human lungs. Air passages in the human body are lined with hair-like cilia, constantly waving back and forth and thus slowly sweeping out any dirt or debris deposited in them (Cohen called them "the moving carpet"). To find how well the lungs cleaned themselves in this fashion, Cohen had a dozen volunteers inhale small amounts of iron oxide dust, which is harmless but can be magnetized.
Over the year that followed the quantity of dust remaining in their lungs was measured periodically, as follows. First each subject stood between a pair of coils, through which a large current was briefly passed. This magnetized the dust grains inside the lungs and lined them up in the same direction; since the grains gradually shifted out of alignment, they needed to be remagnetized at each visit. The subjects then climbed into the shielded room, where the strength of the magnetization of their chest area was measured.
During the year of observations the amount of dust declined steadily in all subjects, first steeply and then more gradually, ending at about 10% of the original level. This showed that the lungs cleaned away debris quite efficiently. The surprise came from 3 additional subjects, added as an afterthought, all of them heavy smokers. Their lungs cleaned themselves much more slowly, and after one year, about 50% of the dust still remained.
Cohen concluded that heavy smoking not only deposited tars in the lungs but also impaired their capacity to clean themselves. He speculated this might explain why a combination of heavy smoking and exposure to asbestos was associated with lung cancer far more frequently than might be expected by simply adding together the effects of smoking and asbestos separately. Not only did the asbestos promote cancer, but the tobacco tars and smoke hampered the natural process by which the lungs were sweeping it away.
Further Reading
Cohen, David et al., Smoking Impairs Long-Term Dust Clearance from the Lung, Science, 204, 514-7, 4 May 1979
For readers with a technical background: A History of Vector Magnetometry in Space by Robert C. Snare, Institute of Geophysics and Planetary Physics, UCLA.
Ness, Norman F., Magnetometers for space research, Space Sci. Rev.,11, 459-554, 1970
Next Stop: 15. Magnetic Reversals and Moving Continents
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