This group previously reported that the operators of RF plastic sealers had a significantly lower heart rate measured during a 24 h period, and more episodes of bradycardia and arrythmia, compared to a control group. In the present study the authors attempted to demonstrate that this might be due to a dysregulation of cardiac autonomic modulation.

The authors used a cross-sectional design. RF operators (18 men, 17 women) and controls (14 men, 23 women) did not have diagnosed heart disease or diabetes, and were not on heart medication. The controls were from the same company as the operators or from companies in the same neighbourhood. Their ages were similar to the operators. The electrocardiogram was recorded during a 24 hour period using a Holter recorder, which was shown not to be affected by RF exposure similar to that used in plastic welding. Heart rate variability (HRV), and total power, including very low frequency (VLF), low frequency (LF), and high frequency (HF), were analyzed. Statistical analysis was made on data from 3 p.m. to 6 a.m., since data were available for all subjects in this period.

There was a significantly increased total HRV and VLF power during nighttime among the RF operators compared with the controls.

The authors considered that these findings could be due to a relative increase in the parasympatheic cardiac modulation. This in turn might be due to an adaptation of the thermoregulatory system to a long-term low-level thermal exposure in the RF operators. The authors put forward the hypothesis that chronic RF exposure might affect the thermoregulatory mechanism, but did not find a dose-response relationship that would have supported this hypothesis. They are unable to dismiss the possibility that the findings could also be due to other confounding factors among the RF operators.