Holter ECG monitoring in patients with perceived electrical hypersensitivity

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Abstract

Earlier studies have indicated that patients claiming to be sensitive to electromagnetic fields, so-called electrical hypersensitivity (EHS), have a dysbalance of the autonomic nervous system (ANS) regulation. This paper focuses on a possible dysbalance in the ANS among EHS patients by the use of long-term monitoring of electrocardiogram (ECG) in both a patient and a matched control group. At the same time, the environmental power frequency magnetic field was recorded for both groups in order to see if there was any difference in exposure between the groups. ECG, heart rate (HR) and heart rate variability (HRV) as well as the magnetic field exposure were monitored for 24 h. Fourteen patients with perceived EHS symptoms were selected from the University Hospital, Umeå, Sweden. Symptoms indicating autonomic nervous dysregulation were not part of the inclusion criteria of the patient group. Age and sex matched healthy subjects were used as controls. No differences were found between the groups regarding magnetic field exposure or the mean HR for 24 h. The HRV analyses showed that the high-frequency (HF) component did not have the expected increase with sleep onset and during nighttime in the EHS group. When separating the sleeping and awake time even less differences between the two conditions in the EHS patients, both for the low-frequency and HF components in the HRV spectrum, were seen. EHS patients had a disturbed pattern of circadian rhythms of HRV and showed a relatively ‘flat’ representation of hourly-recorded spectral power of the HF component of HRV.

Introduction

A significant number of persons are claiming to be sensitive to electromagnetic fields (EMF) with facial skin symptoms, neurovegetative and sometimes ocular symptoms. The phenomenon called electrical hypersensitivity (EHS) has been discussed and investigated for several years in Sweden and some other countries (Bergqvist and Vogel, 1997, Hillert et al., 1999, Rea et al., 1991). An increasing concern has followed the installation of new wireless technologies and rapidly increased exposure to other sources of EMF. The management of EHS and other forms of idiopathic environmental intolerance is problematic since no consistent diagnostic criteria exist. The combination of general neurasthenic complaints and somatic symptoms are unspecific and overlap with many other syndromes like multiple chemical sensitivity, sick building syndrome, fibromyalgia and gulf syndrome (Barsky and Borus, 1999, Sparks, 2000).

Different research approaches to this issue have been tried. Previously we have shown that EHS patients have a dysbalance of the autonomic nervous system (ANS) regulation with a trend to hyper-sympathotonia, as measured by heart rate (HR) and electrodermal activity, and a hyperreactivity to different external physical factors, as measured by brain evoked potentials and sympathetic skin responses to visual and audio stimulation (Lyskov et al., 2001a, Lyskov et al., 2001b, Sandström et al., 1997). These data are in agreement with the physiological findings from other studies on persons with perceived EHS (Rea et al., 1991, Wang et al., 1994, Wibom et al., 1995). These observations indicate a deficiency in adaptive resources and possible predisposition to environmental maladaptation. Provocation studies of these patients have not revealed any worsening of symptoms or physiological reactions related to laboratory exposure to EMF (Lyskov et al., 2001b, Sandström et al., 1993, Swanbeck and Bleeker, 1989). Analysis of heart rate variability (HRV) has become a useful non-invasive tool in the assessment of ANS functions. The balance of sympathetic and parasympathetic activity can be evaluated in several quantitative characteristics of the time and frequency domains. It has been established that the high-frequency (HF) oscillations reflect predominantly parasympathetic influences, but other non-neural mechanisms such as respiratory capacity may also be reflected in these oscillations (Malpas, 2002).

The spectral power of the low-frequency (LF) component is considered to be related to baroreceptor mediated blood-pressure control, and its magnitude (in normalized units) after postural change has been regarded as a marker of sympathetic activity. In general, however, the LF component is assumed to reflect both sympathetic and parasympathetic modulations of the cardiovascular system (Malliani et al., 1991, Task Force of the European Society of Cardiology and North American Society for Pacing and Electrophysiology, 1996). Characteristics of HRV can be used as predictors of cardiac morbidity and mortality (Dekker et al., 1997, Vein, 2000), or influence of occupational stressors (van Amelsvoort et al., 2000).

A lightweight, non-invasive electrocardiogram (ECG) Holter recorder does not limit daily life activity and is easily tolerated by the subjects. It can be used in combination with portable devices for monitoring individual magnetic field exposure. Such a tandem of methods is informative in the study of possible relationships between particular characteristics of magnetic field exposure and ANS functioning.

This paper focuses on ANS characteristics in EHS patients by the use of long-term monitoring of ECG in both a patient and a matched control group. The groups were also monitored for LF magnetic field exposure in their environment.

Section snippets

Study group

All subjects but one were recruited from patients registered at the Departments of Dermatology and Occupational and Environmental Medicine, University Hospital in Northern Sweden, Umeå, Sweden. To be included, subjects should perceive that exposure to video display terminals (VDT), fluorescent tube light and TV set or other electrical sources induced symptoms within 24 h from exposure. The second criterion was that this possible association could not be ruled out or given an indisputable

Results

There was no different in mood over the past week between the two groups, measured by the POMS test.

All the test persons were in sinus rhythm, and only few numbers of ES were recorded, amounting to a total of 0–130 ES during the 24 h recording period. Two patients and two controls had short series of supraventricular ES (<6 beats after each other).

ECG-data in time domain accumulated from 24 h registration did not show any significant difference between the groups, but the EHS group showed

Discussion

The methods of Holter monitoring provides information on HR and HRV, depending on the influence of sympathetic and parasympathetic activity on the sinus node and, therefore, reflect changes in balance of autonomic regulation during the ‘real life’ circumstances. Such examinations have not been carried out previously in patients with perceived EHS.

The major finding of the present study is that patients with perceived EHS had disturbed patterns of circadian rhythms of HRV. In healthy subjects the

Acknowledgements

This work was supported by a grant from Trygg-Hansa, Stockholm, Sweden.

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