Ab0980 Sex-Specific Autonomic Responses to Hyperthermic Radon Therapy in Ankylosing Spondylitis: Insights From Heart Rate Variability Analysis

Background: Each year, over 2500 patients with ankylosing spondylitis (AS) take a series of treatment sessions in the Gastein Healing Gallery (GHG). This setting combines several treatment factors, such as exposure to high humidity (75% to 100% depending on the treatment area), heat (37° to 41° C, resulting in mild hyperthermia), and a low level of radon (44 Bq/m³) in a moderate altitude (1270 m). Mild radon hyperthermia has been shown to have positive effects on rheumatic diseases and osteoarthritis. Hyperthermia alone has several physiological effects, including a reduction of inflammatory processes and changes in the autonomous nervous system (ANS) [1]. The autonomic nervous system is one of the fast-reactive control instances of inflammation and this nervous system-immune system axis has also come into the focus of research in connection with rheumatological diseases [2, 3]. Build on these findings, we analyzed an imbalance in ANS characterized by high sympathetic activity in AS-patients: Heart rate variability (HRV) as a surrogate cardiovagal parameter of ANS was chosen to monitor the course of treatment of AS patients within the clinical routine of the GHG. Objectives: To compare HRV in male and female patients with AS during a series of treatment sessions in the GHG. Methods: 19 women and 21 men with AS (age between 50 and 69 years) completed several sessions (between 6 and 12 for 2 to 3 weeks in total) with a 50 minutes exposure to mild hyperthermia while continuously being subjected to HRV monitoring. Pre- and post-exposure measurements were conducted at rest and compared at the beginning and end of each therapy session. Results: While male patients with AS showed an average increase in the root mean square standard deviation (RMSSD) of around 20% from the beginning to the end of the therapy (14,7 ± 4, 8 ms to 17,7 ± 5, 9 ms), female patients showed a reduction of 14 percent (27,6 ± 13, 6 ms to 23,8 ± 13, 5 ms). As RMSSD (see Figures 1 and 2) indicates the parasympathetic activity of ANS, these results reflect an increased activity of the parasympathetic nervous system in male patients. In contrast, decreased parasympathetic activity was found in female patients after at least five treatment sessions. Other HRV parameters (e.g., LF/HF) also showed a sex-specific effect on the ANS. Conclusion: Comparison of HRV parameters (especially RMSSD and LF/HF) before and after at least five GHG treatment sessions indicates sex influence on HRV in patients with AS. Thus, it can be assumed that GHG therapy has a different influence on ANS depending on sex. It has recently been shown that differences in cardiac autonomic response to heat stress between men and women are related to sex per se. As women's heart is more dependent on vagal autonomic control, heat stress leads to a greater cardiac vagal withdrawal compared to men. In the case of AS, the observed sex-related differences could also be the cause of a different therapy effect on the ANS. Sex-related differences in AS-patients with higher disease activity, functional limitation, and enthesitis score has been reported in females. In addition to differences in the clinical manifestation and disease characteristics, a different response to specific treatments was also observed in AS-patients depending on sex showing a lower efficacy of drug treatments with biologics in female AS-patients. REFERENCES: [1] Flouris AD, Poirier MP, Bravi A, Wright-Beatty HE, Herry C, Seely AJ, Kenny GP. Changes in heart rate variability during the induction and decay of heat acclimation. Eur J Appl Physiol 2014, 114:2119–2128. [2] Tracey KJ. The inflammatory reflex. Nature 2002, 420(6917):853-9. [3] Kelly MJ, Breathnach C, Tracey KJ, Donnelly SC. Manipulation of the inflammatory reflex as a therapeutic strategy. Cell Rep Med 2022, 3(7):100696. doi: 10.1016/j.xcrm.2022.100696. Acknowledgements: NIL. Disclosure of Interests: None declared.