Changes of short-time heart rate variability during hyperthermia treatment with infrared -: A whole-body irradiation

Background: Measures of heart rate variability (HRV) are widely recognized as being an important indicator method for autonomical function and cardiovascular neural regulation. The low-frequency component in spectral analysis is increased during conditions of raised sympathetic activation, the high-frequency component is closely correlated with vagal activity. Whole-body infrared-A irradiation (WBIAI) according to von Ardenne is a newly developed version of hyperthermia. In clinical use peripheral vasodilatation with significant increases in heart rate and hypotension were noted as acute effects of WBIAI. In order to evaluate the effect of WBIAI on autonomic function, we measured HRV during serial hyperthermias. Patients and Methods: Power spectral density analysis of HRV during the first and the last of 4 serial WBIAI treatments with 30-60 min endurance was performed in 10 patients with chronic pain disorders. Tympanal body temperature was recorded continuously and was supposed to increase by 1 degrees C during treatment. Electrocardiographic monitoring was performed using a Marquette Holter EGG. RR data were manually edited and standard frequency domain measures of the first and the last 5 min of treatment computed. The subjective efficacy of the treatment was rated by prestandardized interviews. Results: Body temperature increased by 0.9 degrees C during the first treatment and 1.2 degrees C during the last treatment. In all patients the rise in body temperature due to treatment was accompanied by a significant increase in heart rate and a decrease of arterial blood pressure. During hyperthermia a slight decrease of absolute low-frequency and total power as well as a sharp decrease of high-frequency power and a significant increase of the low/high-frequency ratio could be noted. The rise in low/high-frequency ratio during WBIAI was less distinct at the last treatment compared to the initial treatment. Hyperthermia was regarded as a safe, well-tolerable and effective treatment. Conclusion: The results suggest that the cardiovascular response during WBIAI is accompanied by significant changes in autonomic cardiac regulation: A significant decrease of low-frequency power corresponding to depressed vagal activity results in an increase of low/high-frequency ratio. During serial hyperthermias the acute response is diminished suggesting an adaption of the autonomic response to hyperthermia. Further studies are necessary to investigate the long-standing autonomic effects of the treatment and include analysis of influencing factors such as the lever of physical activity and constitutional individual conditions.