Static, Low-Frequency, and Pulsed Magnetic Fields in Biological Systems

It is presumed that life on Earth has evolved in the presence of natural and ubiquitous magnetic fields, that is, the geomagnetic field and magnetic storms. It is not surprising that biological systems can respond to a wide range of magnetic fields including static magnetic fields (SMFs), low-frequency magnetic fields, and pulsed magnetic fields. Regarding the magnetic sensing mechanism of biological systems, it has been reported that animals can detect small changes in the geomagnetic field by two distinct mechanisms: (1) using the mineral magnetite as the primary sensor and (2) using magnetically sensitive chemical reactions. Several models have been proposed to account for the effects of magnetic fields on biological sensing and reactions. In modern society, there are many sources of electromagnetic fields (EMFs) or
 time-varying magnetic fields. Humans are exposed daily to human-made and naturally originated fields. During the past decade, questions about whether the exposure to EMFs may be linked with adverse health effects have been raised. Although the interaction of nonthermal EMFs, in particular low frequencies up to 300 Hz, with biological systems has been investigated, there is no biophysical mechanism that can explain many of the observed biological effects of low and moderate levels of magnetic fields (<1 T). Proposed mechanisms include effects on electric currents, direct forces on biomagnetic materials, effects on free radicals, ion cyclotron resonance (ICR), charge transfer processes, stochastic resonance, and a dynamical systems/Larmor procession model, etc (see the review by Shigemitsu 2006; Pilla 2007). Recent developments in medical instrumentation such as magnetic resonance imaging (MRI) and transcranial magnetic stimulation (TMS) have raised questions as to whether strong (in the tesla [T] range) magnetic fields influence human health. Medical applications of SMFs of moderate intensities (1–200 mT) for pain reduction and tissue healing have also been studied for many years. Therapeutic applications of permanent magnets and other electromagnetic devices have recently been expanded to various areas such as treatments of pain and diseases like rheumatoid arthritis and cancer. The objective of this chapter is to describe and shed light on some of the more recent information on the biological effects and medical applications of magnetic fields. A discussion of possible implications of these effects on biological systems is also provided. This chapter consists of four sections. Each section contains a comprehensive review of a recent topic of interest. Short summaries of the mechanism of magnetic field action on biological systems and the biomagnetic phenomena are described in Section 3.2, which includes a brief review of well-known mechanisms that are discussed before mentioning the interactions of weak SMFs with biological systems including magnetic sensing and sensing using magnetite as the primary sensor. Section 3.3 reviews and summarizes more recent in vivo and in vitro experimental results of the effects of magnetic fields including TMS and MRI fields. Section 3.4 covers special topics including the response of plants to magnetic fields. In parallel with a comprehensive review on biological effects, the development and medical applications of biomagnetic phenomena are introduced in Section 3.5, and they are reviewed with emphasis on the applications that are currently under investigation.

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