Cardiac autonomic regulation in hyperthyroid subjects during sleep

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Hyperthyroidism, a model of reversible hyperadrenergic state, is characterized by an altered autonomic regulation and by a reduced sleep quality, but no data are available on sleep characteristics and autonomic control during sleep in hyperthyroid (HYPERTH) compared to euthyroid (EUTH) state. The aim of our study was to assess autonomic control during sleep in Hyperth and Euth using symbolic analysis (SA) of heart rate variability (HRV). A polysomnographic study was performed in six women with diagnosed HYPERTH and when recovered to EUTH, after suppression therapy. The time series of RR intervals were constructed for each sleep stage and analyzed using SA, a method that is based on the conversion of time series into symbols, the construction of patterns and the identification of four families: 0V (no variation), marker of sympathetic modulation, 1V, 2LV and 2UV (two unlike variations), marker of parasympathetic modulation. Sleep quality parameters were similar in HYPERTH and EUTH. As to HRV, in Hyperth REM sleep was characterized by an increased 0V% and a decreased 2UV%. Comparing to Hypert, Euthyr showed a decrease of heart rate and sympathetic modulation and an increase of vagal modulation in all sleep stages. In conclusion, in HYPERTH patients, REM is characterized by a predominant sympathetic control and the alterations of autonomic cardiac control during sleep seem to be reverted after treatment.

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