Biomedical Engineering Reference
In-Depth Information
fluorescentmicrographsshowingchangesinactin-containingstress
fibre patterns of the cytoskeleton that span across the cell body and
are attached viaproteins to the innerplasma membrane.
4.4 Weak and Windowed EM Exposure Effects
Over the past decades, a number of reports have emerged of weak,
extremely-low-frequency (ELF) and modulated ELF radiofrequency
(RF) exposures inducing measurable ionic changes in cells. Win-
dowed effects at power densities less than 1 mW cm
−
2
across both
ELFs and RFs have been reported (Adey, 1980; Adey and Sheppard,
1987; Bawin et al., 1989). In the earliest experiments, chick brain
hemispheres in saline solution inside a test tube of about 1.4 cm di-
ameterwereexposedtoELFandmodulatedELFRFfieldsinair(Fig.
4.4a,b). Extracellular tissue fields at ELF are estimated to be 10
−
6
V
m
−
1
(Fig.4.5),andthecorrespondingRFlevelsarearound10Vm
−
1
.
Adey's window experiments resulted in frequency-dependent
changes in intra- and extracellular Ca
2
+
(e
ux/influx) concentra-
tion levels both at ELF and modulated ELF frequencies (Bawin
et al., 1975; Bawin and Adey, 1976; Liboff et al., 1987). The
original observations in which in vitro specimens were exposed
in air remain controversial. Since the observations were not
understood mechanistically using classical electromagnetics (CEM)
theory, there was question within the bioeffects community about
the validity of these effects at weak exposure levels. There was
further controversy as the modulated effects appear at levels below
thosesetdownbynationalandinternationalRFexposurestandards,
such as the International Radiation Protection Association (IRPA),
the Standards Association of Australia (SAA) and the American
NationalStandardsInstitute(ANSI),whileELFeffectsoccuratmuch
weaker levels. SFT in contrast to CEM suggests that such effects
may be mechanistically understood and suggests further that the
effect at these weak levels may indeed constitute a possible health
hazardandisnotjustaninterestingbioeffect.Thisopinionisrelated
to possible effects upon cellular division. Public concern demands
further study to provide a clear and quantitative understanding.
In Chapter 6 we examine the use of PEMF-based therapies that
