Ageing and thalassotherapy : Effect on heart rate variability

The aging processes are known to impair many of the physiologic mechanisms that regulate heart rate and blood pressure. This can lead to an inefficient adaptation to hot environments, presumably due to a decreased baroreflex sensitivity. However, warm water immersion is still widely used in thermal treatments (Thalassotherapy), and it is largely prescribed by general practitioners in elderly people. Nevertheless, to date the cardiovascular adaptations to warm water immersion is poorly addressed, as most study were performed at cold or neutral temperature. Aim of this study was to assess the changes in various physiological parameters during immersion in thermal pools containing sea water at warm (35° C) temperature and different salinities. Measurements were performed in 14 female subjects, in lying position, before entering the pool and during water immersion. O2 consumption, heart rate, pulmonary ventilation and body temperature significantly, although slightly, increased during warm water immersion, whereas systolic and diastolic blood pressure significantly decreased. Significant changes of HRV in the frequency domain were also observed, with a decrease of HF and an increase of VLF recorded during immersion in the pool with the highest salinity only. LF was scarcely influenced in all experimental conditions. A significant negative correlation between percentage body fat and body surface-tympanic temperature gradient was also observed during immersion. The observed adaptations differed from those previously recorded in cold water. Warm water immersion most likely causes a decrease of parasympathetic tone, aimed at increasing heart rate without causing vasoconstriction. The effect of salinity deserves further investigation.