The Influence of Magnetic Fields on Man
The human body is composed of atoms of different elements surrounded by water molecules. These atoms react to magnetic and electric forces and fields, and this may lead to, for example, a net-nuclear magnetization of a person when placed in a clinical MRI machine. It is therefore easy to imagine that magnetic and electromagnetic forces could alter physiologic functions, induce effects, or influence the organism in either a positive or negative way. Although the extent and importance of these phenomena has been under investigation for the past 100 years, the effects observed have generally been minimal and seldom statistically significant. A report of the American National Research Council which examined more than 500 studies spanning 17 years of research concluded, in 1996, that ''No conclusive evidence shows that exposures to residential electric and magnetic fields produce cancer, adverse neurobehavioral effects, or reproductive and developmental effects'' (National Research Council, 1997). A more succinct overview, but with the same conclusions, was provided by Tenforde (2003).
When investigating magnetic effects on humans, two different magnetic field ''types'' are generally distinguished: (1) a static magnetic field, which exists around a large magnet; and (2) a magnetic field that is pulsed at frequencies higher than 10 Hz, often abbreviated as EMF (electromagnetic fields). The study of these effects is termed "biomagnetism", some sub-fields of which are highly controversial, while others have already been established in medical applications (see Chapter 2).
Most scientists agree that static magnetic fields of up to 10 Tesla have no obvious effects on long-term plant growth, mouse development, body temperature, or brain activity (Barnothy et al., 1956; Barnothy and Barnothy, 1958; Maret et al., 1986). Such conclusions echo findings made more than a century ago, at which time, Mr. Kennelly - the chief electrician at the Edison Laboratory - wrote, after exposing a volunteer to 27 000 times the magnetic field of the Earth, that, ''... the human organism is in no wise appreciably affected by the most powerful magnets known to modern science; neither direct nor reversed magnetism exerts any perceptible influence upon the iron contained in the blood, upon the circulation, upon ciliary or protoplasmic movements, upon sensory or motor nerves, or upon the brain.'' (Peterson and Kenelly, 1892) (Fig. 1.11).
The lack of any apparent effects of strong magnetic fields on humans placed near powerful magnets does not imply that there are no effects at all. It would
also be foolish to conclude that humans have no magnetosensitive organs. During the past years, evidence has been mounting that not only do pigeons (Keeton, 1971), bees (Kirschvink et al., 1992a) and fin whales (Walker et al., 1992) possess magnetic receptors, but humans might also (Kirschvink et al., 1992b). Chains of magnetite particles similar to those known from magnetic bacteria and algae have been found - chains which supposedly are either a part of, or form the magnetosensitive organ itself. Several research investigations have been conducted in an attempt to show that humans have a ''magnetic sense''. One study reported an experiment in which students were driven around blind-folded and then asked to point in the direction of their dormitories. Those students who used only their natural ''magnetic sense'' had a higher success rate than those whose ''magnetic sense'' had been deceived by the field of a magnet attached to their heads (Baker, 1989). Clearly, further research is needed in this area as the results are often contradictory and suggest several interpretations.
Research indicates that humans are sensitive to small changes in magnetic field gradients, but not to the overall magnetic field (Rocard, 1964). Evidence supporting this has come from studies of the dowser reflex. A dowser, a person holding firmly onto a divining rod (see Fig. 1.12) will, under certain physical conditions, experience a force which results in an involuntary upward or downward movement of their rod. To skeptics the movement appears illusory, to believers it appears magical, but the effect has been consistently reported over the past 70 years by a number of authors. In the most-often performed experiment, a group of dowsers was made to walk along the same stretch of street. At points within 1 or 2 m of each other, they all had their divining rods pulled down to the earth.
Magnetic field measurements have shown that the dowser reflex occurs when the dowser passes through a region where the Earth's magnetic field is not entirely uniform. This field anomaly produces a magnetic field gradient, which must exceed 0.1 mOe m_1 (8 mA m~2) to be detected. The speed with which the dowser
passes through this field gradient also influences their magnetic reception. The dowser must pass through a 0.1 mOe m_1 field gradient within at least 1 s in order to detect it. Furthermore, the detection level can be increased by adding up the small differences in field gradients. Higher magnetic field gradients, however, lead to saturation and can only be detected by moving faster. Of additional interest is Rocard's notion that although most people are sensitive, a good dowser has a more accurate and rapid reflex than the bad dowser.
Physiological explanations of the dowser reflex have included the physiological induction of magnetic moments, electromagnetic currents, and nuclear magnetic resonance. None of these possibilities has, however, been able to account convincingly for the phenomenon, and thus the search for an explanation continues.
Electromagnetic machines produce fields and field gradients which are constantly changing and which have been found to influence humans. The earliest experiments to test the effects of these fields using humans were performed at the end of the 19th century. D'Arsonval's experiments were among the most spectacular (Rowbottom and Susskind, 1984). In one of these experiments, a person was completely enclosed in a large solenoid resembling a cage, and insulated from all contact with it (Fig. 1.13). Owing to the high-frequency oscillating magnetic field within the solenoid, strong currents were induced within the subject's body, and
although neither pain nor any other sensation was felt, a lamp held in the person's hands became incandescent during the procedure. D'Arsonval called this method of applying high-frequency currents to man ''autoconduction''.
As the 20th century began, the serious investigation of the physiologic consequences of electromagnetic fields became tainted by association with quack science and the pseudo-technology of electromedicine. Dr. Albert Adams (1863-1924), one of the controversial therapists applying electromedicine, was named ''Dean of 20th century charlatans'' by the American Medical Association. Adams postulated that each organ system and each patient were tuned to a characteristic electromagnetic wavelength. It should therefore have been possible to diagnose medical conditions and to deliver therapy to individuals hundred of miles away simply by using a properly tuned, radio-based device. This therapy was called ''physiologic frequency manipulation'', and it aroused public interest in bioelectricity and electromagnetic physiologic effects. The science community gradually lost interest in bioelectricity, but before its fall from grace, the groundwork was laid for such major clinical applications as electroconvulsive therapy, cardioversion, and transcutaneous nerve stimulation, all of which are discussed in greater detail in Chapter 4.
Between 1930 and 1960, the physiological and biological effects of electromagnetic fields were studied only minimally. Research accomplished by the small group of investigators who continued working in this area was reviewed comprehensively by Barnothy during the late 1960s (Barnothy, 1964, 1969). Although the design of many of those studies performed up to this time was flawed, some of their results have been confirmed by more stringent research. For example, results recently endorsed in a report by the National Research Council (1997) support previous findings that electromagnetic fields induce changes in the brain's electro-encephalographic (EEG) activity (Bell et al., 1991), produce measurable changes in polypeptide synthesis in salivary glands (Goodman and Henderson, 1988), and are able to influence the levels of calcium and melatonin in cells exposed to highlevel fields (Graham et al., 1996). Additionally, recent double-blind studies have confirmed the effects of low-frequency pulsed electromagnetic fields greater than 0.5 mT on growth induction in bone. Indeed, their use is now the treatment of choice for certain recalcitrant problems of the musculoskeletal system, including salvage of surgically resistant nonunions in children and adults and chronic refractory tendinitis (Bassett, 1989).
Available data indicate that humans are susceptible to alternating electromagnetic fields. Epidemiological studies even suggest health effects attributable to relatively small magnetic fields such as those found underneath a high-voltage line (Jauchem, 1995). The report of the National Research Council, for example, acknowledged a 1.5-fold higher incidence of childhood leukemia in homes situated close to high-voltage power lines, though the examined studies failed to show a statistically significant association between exposures and disease (National Research Council, 1997). Unless new theories for these effects are proposed on the grounds of molecular mechanisms, it will be very difficult to either prove or disprove any association between disease and the small magnetic fields produced near electric devices, machines and power lines. Even the electromagnetic fields in heavily industrialized regions amount only to a few tenths of one mTesla, which is less than 1% of the ambient terrestrial magnetic field. Most experts would not anticipate any serious effects related to these additional magnetic fields.
Current laboratory investigations employ more sophisticated techniques, more sensitive instruments and more refined statistical methods than ever before. When combined with our deeper understanding of magnetic resonance patterns in tissues (see Chapter 3), this vastly improved instrumentation should provide a strong base from which to improve our understanding of the electromagnetic field effects at the cellular and molecular levels. In time, this will likely lead to the introduction of new, magnetism-based medical techniques for diagnosis and therapy.
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