With the increasing use of cellular telephones, the potential influences of radio-frequency electromagnetic fields (EMF) on human well-being
are a focus of public interest. Seven healthy men and three women volunteers aged between 26 and 36 years underwent a single-blind
placebo-controlled protocol to investigate the influence of the EMF of a mobile telephone (GSM 900 MHz, 2 Watt, 217 Hz frame repetition
rate) on blood pressure (BP), heart rate (HR), capillary perfusion (CP), and subjective well-being. The telephone was fixed in a typical position
on the right-hand side of the head and operated by remote control, so that the volunteer did not know whether or not the phone emitted EMF.
BP and HR were measured continuously with a Finapres device and CP with an infrared plethysmograph on the right hand. The protocol was
divided into phases with placebo and with EMF exposure of 35 min each. A fixed sequence was chosen instead of a randomised order, because
of the possibility of an effect of EMF beyond the exposure time. The participants were told, however, that a randomised sequence would be
applied. To reduce intraindividual variability1 each participant underwent the same protocol five times on different days.
After 35 min of exposure, values during supine rest and responses to standing up over 60 s, deep breathing with 6 breathing cycles per minute,
and Valsalva manoeuvre with 40 mm Hg expiratory pressure were measured as reported previously.2 Phases I and III of
the Valsalva manoeuvre are characterised by passive changes of BP induced by changes of intrathoracic pressure at the beginning and just after
the end of the pressure phase: BP changes in phase II, end of phase II, and phase IV represent the neuronally mediated response of the
autonomic nervous system to counteract the induced falls in BP.3 Well-being was assessed with a visual analogue scale at
the beginning and the end of both periods.
|
Mean and SD of systolic (SBP), and diastolic (DBP) blood pressure (mm Hg) and heart rate (HR in bpm) with and without exposure to
an electromagnetic field.
*Absolute values + if the differences from baseline differed significantly between placebo and EMF exposure. bpm=beats per minute.
*p<0·05, **p<001, ***p<0·001, ****p<0·0001.
No statistically significant influence of EMF on subjective parameters was found. During EMF, systolic and diastolic BP at rest were
significantly higher in comparison to placebo exposure (figure). After 30 s and 60 s standing upright, absolute BP values were significantly
higher under EMF exposure, but not the corresponding differences to resting values. Thus, BP during standing paralleled the increase of values
at rest. During the Valsalva manoeuvre, the differences of BP from values at rest were significantly lower during phase I and significantly higher
during phases II and IIe, whilst absolute BP values showed no significant differences. Considering that the rise of BP in phase I is due to the
increased intrathoracic pressure and that the decreases in phases II and IIe are induced by reduced venous return, with both mechanisms being
constant in both parts of the protocol, the BP findings during the Valsalva manoeuvre can be explained by the increase of BP at rest. During
all manoeuvres, CP measurements showed a significantly more pronounced vasoconstriction (p<0·01). Absolute HR values decreased
significantly during rest and all manoeuvres (Valsalva manoeuvre HR increase 99·66 [SD 16·69] vs 95·55
[17·00], p<0·05; deep breathing HR variation: 20·56 [5·03] vs 18·84 [4·51],
p<0·05).
We conclude that exposure of the right hemisphere to a radio-frequency EMF for 35 min causes an increase in sympathetic efferent activity
with increases in resting BP between 5 and 10 mm Hg, most likely due to more pronounced vasoconstriction. Baroreflex-mediated BP regulation
during standard autonomic function tests was not influenced.
1 Braune S, Schulte-Mönting J, Schwerbrock S, Lücking CH. Retest variation of cardiovascular parameters in autonomic
testing. J Auton Nerv Sys 1996; 60: 103-07.
2 Braune S, Auer S, Schulte-Mönting J, Schwerbrock S, Lücking CH. Cardiovascular parameters: sensitivity to detect
autonomic dysfunction and influence of age and sex in normal controls. Clin Auton Res 1996; 6: 3-15.
3 Bennarroch EE, Opfer-Gehrking TL, Low PA. Use of the photoplethysmographic technique to analyse the Valsalva manoeuvre in
normal man. Muscle Nerve 1991; 14: 1165-72.
Neurologische Universitätsklinik Freiburg, 79106 Freiburg, Germany (S Braune); and Deutsche Telekom AG,
Technologiezentrum, Darmstadt
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