Magentic and Electromagnetic Therapy In Horses
 

David W. Ramey, DVM
P.O. Box 5231
Glendale, CA 91221
 
 

INTRODUCTION

There are numerous products and therapies available with which horse owners can treat their horse. One of the more popular, at least if the number and quality of advertisements for the products is any indication, is the application of a magnetic field. Although the biological effects of low-level magnetic fields have been studied since the 1500s, there is still no consensus as to whether these effects have any physiological significance. From a scientific standpoint, however, the claims made for and the lack of any scientific evidence for effectiveness of the products for treating horses is troubling.

HISTORY

Magnetic therapy is nothing new. The effects of magnets on biologic processes have been discussed for over 2000 years! The idea that magnetic therapy could be used to treat disease began in the early 16th century with the Swiss physician, philosopher and alchemist Paracelsus, who used magnets to treat epilepsy, diarrhea and hemorrhage. Magnetic therapy really took off in the mid-18th century when Franz Mesmer, an Austrian doctor who also helped began the fields hypnotism and psychoanalysis (and from whose name the word "mesmerize" was coined) opened a popular magnetic healing salon in Paris in 1777 to treat the untoward effects of the body's innate "animal magnetism." From there, in spite of intense condemnation from the scientific community, the race to use magnets to heal was on.

Over the next couple of centuries, magnetic therapy developed into the worst form of quackery. In 1799, Elisha Perkins, a Connecticut physician and sometime mule trader, began advocating the use of "metallic tractors" for the treatment of various areas in people and horses. The user of the tractors (small metal magnetic wedges) had merely to sweep the tractors over the injured area for a few minutes to "draw off the noxious electrical fluid that lay at the foot of suffering;" the benefits from the devices were seen amazingly quickly. There were glowing testimonials from experts and supporters of the tractors and Perkins became very rich (unfortunately, the magnetic tractors were unable to keep Dr. Perkins from a premature death due to yellow fever in 1799).

More magnetic opportunities soon followed. The Sears catalogue advertised magnetic boot inserts in the late 1800s. A full line of magnetic caps and clothing (with over 700 magnets!) was available by mail order during that same period from Thatcher's Chicago Magnetic Company. Dr. Thatcher asserted that "magnetism properly applied will cure every curable disease no matter what the cause." At the turn of the 20th century, Dr. Albert Abrams (who was referred to by the American Medical Association as the "Dean of 20th Century charlatans"), made millions by postulating that each organ system and patient were "tuned" to characteristic electromagnetic wavelengths. By the time the second World War rolled around, however, the physiologic effects of electromagnetic fields were no longer receiving much attention in academic medical journals.

All of this long and unbridled history of clear quackery regarding the using magnets to heal people has tended to obscure the fact that there is and has been a great deal of relatively recent medical investigation as to the real effects of magnetic and electromagnetic fields on body tissues. From a biophysics standpoint, it's very important to separate the two therapies; magnetic does not equal electromagnetic.

ELECTRICITY AND MAGNETISM

Electromagnetism was first discovered in the 1800s by the English physicist Michael Faraday. Faraday found that by running an electric current through a wire coil that a magnetic field could be generated. Conversely, a changing magnetic field can generate an electric voltage (the magnetic field must change to have any electrical effect). Hence, the term pulsating electromagnetic field (PEMF) therapy, which generates rising and falling levels of a magnetic field.

Importantly, the biological effects of PEMF therapy that are reported are thought to be electrical: not magnetic. Magnetism generates a voltage in tissue according to the equation:

V = n x a x dB/dt

V = Voltage
n = number of turns in the electromagnetic coil
a = area of the loop
dB/dt = The rate of change of magnetic field with respect to time. B is the symbol usually used to represent a magnetic field (in Teslas). For example, if B goes from zero to 1 Tela in 1 millisecond, then dB/dt = 1000 Teslas/sec.

A static magnetic field (that is, one that doesn't change) cannot generate an electrical voltage. When calculating the electrical effect of a static magnetic field using the voltage equation above, dB, the rate of change of the field, is zero, as will be the voltage induced by the field. Thus, if there are any effects of a static magnetic field on tissue, those effects cannot be electrical.

PULSATING ELECTROMAGNETIC FIELD THERAPY

Extracellular matrix synthesis and repair is subject to regulation both by chemical agents (such as cytokines and growth factors) and physical agents, principally mechanical and electrical stimuli. The precise nature of the electromechanical signal is not known, however. In bone, mechanical and electrical signals may regulate the synthesis of extracellular matrix by stimulating signaling pathways at the cell membrane., In soft tissue, alternating current electrical fields have been shown to induce a redistribution of integral cell membrane proteins. Hypothetically, this could initiate signal transduction cascades which could in turn cause a reorganization of cytoskeletal structures. The various suggestion that electrical signals may be responsible for information transfer to the cells of any tissue has neither been proven nor disproven, however.

There is electrical activity going on in the horse's body at all times. For example, electrical currents can be measured in the beating heart. They are also generated in the production of bone, in which endogenous electric current densities produced by mechanical loading under physiologic conditions approximate 1 Hz and 0.1 - 1.0 A/cm2 . Thus, it is theorized that application of the appropriate amount of electrical current, either directly (through the application of electric wires) or indirectly (via indirect induction via a magnetic field) may affect body tissues in a number of ways. The word appropriate in the preceding sentence is especially important, since cells and tissues respond to a variety of electrical signal configurations in a way that suggests a degree of specificity for both the tissue affected and the signal itself.

The most widely studied application of electromagnetic field therapy in human medicine is in fracture therapy. Although no one knows how they may work at the cellular level ,a number of studies have suggested that electrical fields generated by PEMF therapy are stimulatory to biologic processes pertinent to osteogenesis, , and bone graft incorporation., PEMF therapy is currently only approved for the treatment of delayed and non-union fractures in human patients in the U.S. by the United States Food and Drug Administration and the effectiveness of the treatment is supported by at least two double-blinded studies. , Applications of PEMF therapy have also been studied in fresh fractures, however, at least one study shows that healing of fresh fractures is actually delayed with PEMF therapy.

PEMF therapy has also been evaluated in soft tissue therapy. Some studies suggest that PEMF therapy may be of value in promoting healing of chronic wounds (such as bedsores) , in neuronal regeneration, , and in many other soft tissue injuries., A recent study of PEMF therapy in an experimental Achilles tendonitis model in rats concluded that there was an initial decrease in water content in injured tendons but that all treated groups were equal to controls by 14 days. PEMF therapy may have limited value for the treatment of tendon injuries, perhaps in part because there is no apparent electrical activity to affect in these tissues.

On the other hand, other investigators have been unable to show any effect of the low-level electromagnetic fields used to promote tissue healing. For example, one study was unable to show that applying a magnetic field to a non-healing fracture offered any advantage over just waiting and concluded that the long periods of immobilization and inactivity required for the application of the therapy were as likely as the PEMF treatment to be responsible for healing. Criticism of PEMF studies has been directed at the fact that some of the studies are poorly designed, that independent trials have not been conducted to confirm positive results and that the electrical fields induced by the machines are several orders of magnitude lower than what would be required to perturb the naturally occurring fields that occur across biological membranes. Even proponents of the therapy concede that much work needs to be done to optimize such variables as signal configuration and duration of treatment before PEMF therapy can be generally recommended.

STATIC MAGNETIC FIELD THERAPY

Magnetic pads that radiate an unchanging magnetic field can be applied to horse limbs via any number of boots, blankets or pads. They also come with a variety of beneficial claims of efficacy that appear to be completely unsupported by scientific studies attesting to their efficacy. Nor is the mechanism of action by which such devices should have an effect clear. As previously mentioned, because the static magnetic fields don't change, there can be no electrical effect. Thus, proponents of applying magnets to injured or sore tissues have to use another mechanism to explain the purported beneficial effects. That mechanism is generally described as an increase in local blood circulation. Unfortunately, the scientific evidence in support of this explanation is tenuous at best.

Blood (indeed, all the tissues of the body) contains electrically charged ions. A physics principle known as Faraday's Law states that a magnetic field will exert a force on a moving ionic current. Furthermore, an extension of Faraday's law called the Hall effect states that when a magnetic field is placed perpendicular to the direction of the flow of an electric current flow, it will tend to deflect and separate the charged ions. The deflection of the ions will be in opposite directions depending on the magnetic pole encountered and the charge of the ion. However, this force is not based on the attraction of like and unlike charges.

The Hall effect implies that when a magnet is placed over flowing blood in which ionic charges such as Na+ and Cl- do exist, some force will be exerted on the ions. Furthermore, the separation of ionic charges will produce an electromotive force (EMF). An electromotive force is a voltage between points in a circuit; in theory, this produces a very small amount of heat. These physical effects, which do exist, are the basis for a quasi-scientific theory for the purported effects of static magnetic field therapy that deserves closer inspection. To whit:

"When a magnetic field with a series of alternating North and South poles is placed over a blood vessel, the influence of the field will cause positive and negative ions (for example, Na+ and Cl-) to bounce back and forth between the sides of the vessel, creating flow currents in the moving blood not unlike those in a river. The combination of the electromotive force, altered ionic pattern and the currents causes blood vessel dilation with a corresponding increase in blood flow. "

The problem with using Faraday's law and the Hall effect to explain the purported effects of static magnetic pads is that the magnitude of that force applied by the field is almost infinitesimally small. This is primarily because of two reasons. First, the magnetic field that is being applied to the tissue is extremely weak. Secondly, the flow of the ionic current (the blood) is extremely slow, especially when compared to the flow of electric current. However, it is possible to estimate the forces applied to flowing blood by a weak magnetic field, as long as the strength of the magnetic field applied, the velocity of the flowing blood and the number of the ions in the blood are known.

Magnetic field strength is measured in one of two units: 1 Tesla = 104 Gauss. The magnetic field strength of a Norfield's MAGNETIChockwrap was measured at California Institute of Technology as having a field strength of 270 Gauss at the level of the pad and of 1 Gauss at a distance of 1 cm from the pad (tissue purportedly affected by the pads would lie at least 1 cm from them; 1 Gauss is approximately the magnetic field strength of the earth); promotional information for Bioflex pads asserts an "independent laboratory" has measured the field strength of their pads at 350 Gauss asserts and that "optimum" field strength for their purported healing effects is less than 500 Gauss. Regardless, these are very weak magnetic fields. The velocity of blood flow is considered to be from 0.5 to 1 cm per second.

Generously considering the applied magnetic field at 250 Gauss (0.025 Tesla) and the velocity of blood flow v as 1 cm/sec (0.01 m/sec), the electric field seen by an ion in the blood flow can be calculated as:

= v x = 2.5 x 10-4 Volts/meter/sec

Hence, the change in electric potential (a psuedo Hall effect) across a 1 mm diameter blood vessel can be estimated at a minuscule 2.5 x 10-7 Volts.

Ions of opposite charges will be separated in opposite directions when moving through a static magnetic field. The separation of charges, known as the drift velocity, can also be calculated. In the case of Na+ and Cl- ions in flowing blood under the influence of a 250 Gauss magnetic field, the increased separation of the positive sodium and the negative chlorine ions will be about 0.2 Angstroms per second, or about 1/10 the diameter of an atom. This can be compared with the random drift distance in one second that comes from the thermal agitation imparted by the heat of the horse's body of about 0.25 mm/sec. Stated in another fashion, the ions will travel further from thermal agitation than from the 250 Gauss magneto-electrical field drift by a factor of about 10 million.

At least one manufacturer of magnetic pads asserts that they are able to increase the effect of charge separation by alternating north and south magnetic poles. Alternating magnetic poles are most commonly seen in refrigerator magnets. By alternating the magnetic poles, an increased magnetic gradient is created, which increases the ability of the magnets to stick to the refrigerator. Paradoxically, alternating poles decreases the magnetic field strength of the magnet because the fields tend to cancel each other out as they extend from the magnet. Thus, while, alternating poles would exert opposite forces on ions flowing through the magnetic field, the decrease in magnetic field strength would lessen any potential influence of the magnetic field on the target ions.

Further proprietary design information regarding Bioflex pads would also appear to be irrelevant insofar as having biologic effects. Promotional information for the pads states that a "concentric circle" arrangement of the pads increases the likelihood that the applied magnetic field would be applied in a manner perpendicular to flowing blood (which would be necessary to maximize the Hall effect). In fact, since blood vessels run randomly throughout the three dimensions of the tissue, it is a geometric fact that there can be no "preferred" arrangement of the magnetic field that favors a perpendicular orientation of that field.

Any magnetic forces generated by a static field affecting fluid movement in a blood vessels would have to overcome both the normal, pressure-driven turbulent flow of blood propelled by the heart and as well the normal dancing motion of particles suspended in a liquid due to thermal agitation (known as Brownian movement). Given the strong physical forces that already exist in a blood vessel, any physical forces generated by a static magnetic field on flowing blood, particularly those as weak as those in therapeutic pads, are almost undoubtedly irrelevant insofar as having any biological effect.

MAGNETIC FIELDS AND BLOOD FLOW

A number of studies have investigated the effects of static magnetic fields on blood flow. Studies commissioned by Bioflex magnetic pads showed an increase in the flow of a concentrated saline solution (five times as salty as normal blood) thorough a glass capillary tube that was exposed to a magnetic field (for some reason, the word glass appears to be routinely omitted from promotional material in support of the pads). This study has been often cited as evidence that magnetic field therapy can potentially affect the circulation of blood in the horse's system. However, the mechanism for the increase in saline flow is not apparent; it certainly could not have been related to any dilatory effect on the walls of the glass capillary tube. Says Dr. George Pratt, Professor of Electrical Engineering at the Massachusetts Institute of Technology, who performed the study, "Yes, we did some experiments with them [magnetic pads] on a saline solution - they did seem increase the flow of saline through a glass tube. I think it's a long extrapolation to say that the experiments that we did on saline have anything to do with blood. I rather think that it's all black magic and smoke and mirrors. I wouldn't count on curing anybody with those pads."

A second study, commissioned and paid for by another purveyor of magnetic pads, evaluated the effects of the pads using nuclear scintigraphy, a technique that is useful is identifying areas of blood vessel dilation and inflammation. That study concluded that, "Scintigraphy was performed in the vascular, soft tissue and bone phase using a cross over trial to demonstrate increased blood flow and metabolic activity as a result of the local application of a permanent magnetic pad on the equine metacarpus. A highly significant increase was evident in the three phases." The company that makeS the pads has widely touted this study as confirming that magnetic pads promote blood circulation to the areas under the pads.

This study, which is apparently the only one to state that a static magnetic field affects blood circulation, is open to criticism. The dosage of Tc99 used in the study was approximately twice the normal dose used in diagnostic scintigraphy studies. The experimental model, which compared the results of scans on one "treated" limb vs. the non-treated limb is inherently inaccurate, since one forelimb cannot be used as a control for the other in scintigraphic studies (each limb should be used as its own control). Finally, the design of the study, in which a bandage and magnetic pad was applied to one limb and a bandage only was applied to the other, was flawed. (Other studies have compared the effects under magnetized and demagnetized pads). It is reasonable to question whether the results of this study validated the research methods used by the authors.

However, numerous other studies have failed to show any effect of magnetic fields on blood circulation. No effect of dental magnets on the circulation of blood in the cheek could be demonstrated (the forces of repulsion or attraction created by magnets can help move teeth). Mice exposed to two strengths of PEMF and tested by scintigraphy were unable to demonstrate any circulatory effects. A study on the circulatory effects of a magnetic foil was unable to show any effect in the skin of human forearms. A study in horses showed that application of a magnetic pad over the tendon region for 24 hours showed no evidence of temperature increase in treated limbs vs. placebo controlled limbs, using thermographic measurements that would have presumably shown an increase in blood circulation to the area. Application of a magnetic foil to healing wounds in rats showed no significant effects.

On a more practical matter, if a magnet did cause local increases in circulation, one would expect the area under the magnet to feel warm or get red as a result. Such an effect is not reported when magnets are held in the hand. Furthermore, one would expect any circulatory effects produced by very weak magnetic fields to be magnified in stronger magnetic fields. However, in magnetic resonance imaging (MRI) machines, in which the magnetic forces generated are two to four orders of magnitude greater than those produced by therapeutic magnetic pads, no circulatory effects have every been reported. In studies using in which humans were exposed of magnetic fields up to 1 Tesla (10,000 Gauss) there was no evidence of alterations in local blood flow at the skin of the thumb or at the forearm. Even a 10 Tesla magnetic field is predicted to change the vascular pressure in a model of human vasculature by less than 0.2% and experimental results of the effects of strong magnetic fields on concentrated saline solutions are in general agreement with these predictions.

One is forced to conclude that if there is an effect of static magnetic fields on body tissues, there is no known biological mechanism by which that effect is generated. That's not to say that there is no effect; one study has shown that there is a strong placebo effect at work with magnetic therapeutic devices in humans. One may also postulate that the boots, blankets and bandages in which the magnets are sewn have some sort of a thermal effect that is independent of the magnetic field (and could be duplicated with any form of bandaging).

CLINICAL APPLICATIONS OF MAGNETIC FIELDS IN HORSES

PEMF therapy is typically applied to horses via boots or blankets. Some of the variables of the magnetic field generated (such as the amplitude and frequency of the signal) can be controlled using this form of magnetic therapy; importantly, changes in these variables appear to affect different tissues in different ways and those ways are not well-defined.

The other way to apply a magnetic field is by strapping or nailing on a magnetic pad. This form of therapy generates a continuous, static magnetic influence on the targeted tissue, however, the magnetic field cannot be modulated. The principle advantage of this form of magnetic therapy is that it is relatively inexpensive (compared to the PEMF machines) and easy to apply; the disadvantage is that no one seems to be able to prove that it does anything.

The absence of a plausible scientific theory for a mechanism of action should never override reliable strong clinical evidence of an effect. However, there appear to be no published scientific studies available that demonstrate that magnetic field therapy, whatever the form, is valuable in the treatment of disease conditions of the horse. Daily electromagnetic therapy did increase the concentration of blood vessels in surgically created defects of equine superficial digital flexor tendon but the maturation of the repair tissue and the transformation of collagen type (two essential components in the healing process of tendon) actually were delayed by the treatment in samples collected at 8 to 12 weeks after surgery. No benefit could be demonstrated in the healing of freshly created bone injuries treated with pulsating electromagnetic field therapy when compared to untreated control limbs, although another study did suggest an increase in bone activity under PEMF treatment when holes were drilled in horse cannon bones. Topical treatment with a pulsed electromagnetic field showed little effect on metabolism of normal horse bone in another study. Unfortunately, the principle application of PEMF therapy in people, for delayed and non-union fractures, is of little apparent use in horses.

DISCUSSION

Whenever an injury to tissue occurs, the goal of any medical therapy is to help allow healing of that injury so that, to the extent that it can be done, the injured tissue is returned to full normal function as quickly as possible. The quality of tissue repair and the speed with which that repair can be accomplished are the two major variables in the healing of any injury. Any medical therapy that could be demonstrated to affect either variable (or better yet, both of them) would be extremely valuable to the medical field.

However, assessing whether or not a particular medical therapy is effective in those regards is somewhat problematic. The old adage, "Time heals all wounds," is largely true. According to one source, approximately 70 per cent of all acute medical conditions of the horse will heal themselves with no intervention whatsoever. That means that whatever method of treatment is selected, 7 out of 10 times, the problem that is being treated will get better. If healing occurs while a device that is touted to promote healing is applied to the injured area, that device often receives the credit.

Unfortunately, the public appears to have no protection against dubious but persuasively presented claims which are often wrapped in scientific terms to give them an air of believability. Explanations that magnetic fields "increase circulation," "reduce inflammation," or "speed recovery from injuries" are simplistic and are simply not supported by the weight of experimental evidence. The effects of magnetic fields on body tissues are quite complex and not well understood. The effects vary from tissue to tissue and from different intensities and duration of the magnetic field applied. Although the therapies may be harmless (at least there are no reports of harm from the devices in the equine scientific literature) that does not also mean that they are worth a try.