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Braune and colleagues repeated their earlier study in which they had found an increase in blood pressure in subjects exposed to an EMF. That study, however, had been criticized on the grounds that there was no randomization of exposure sequence. All subjects had been sham-exposed first. On this occasion they tested 40 healthy volunteers (equal number of men and women). Each subject was tested on two different days. On the first day, each subject had a period of sham-exposure and a period of EMF exposure, given in a randomized sequence. On the next day the same subject would have the reverse sequence of exposure. The subjects were unaware of what type of exposure they were receiving at any given time. The EMF was generated by a GSM phone at 900 MHz. The SAR was 0.50 W/kg averaged over 10 g of tissue and 0.84 W/kg when averaged over 1 g of tissue. Each experiment started with 30 minutes of baseline readings, followed by 20 minutes of supine rest, then 10 minutes in a 70° upright tilt position and a second 20 minutes of supine rest. A 15-minute interval in supine rest then separated the two periods of exposure and sham-exposure. Measurements were made continuously of blood pressure (BP), heart rate and capillary blood flow velocity. Norepinephrine, epinephrine, cortisol and endothelin serum levels were measured after the initial resting phase and subsequently every 10 minutes. There was a statistically significant increase in systolic and diastolic BP of about 5 mms Hg each during the two periods, but this was independent of exposure to EMF. There was a decrease in norepinephrine and cortisol levels during the two periods. In summary, the EMFs emitted had no effect on the outcomes studied. The authors surmise that the increase in BP could be related to adaptation to fluid shifts occurring in the body when someone assumes a supine position. It is likely that the blood pressure increase observed in the 1998 Braune study was related to the same mechanism. |
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