Basal sympathetic predominance in periodic limb movements in sleep after continuous positive airway pressure

Purpose This study investigated the basal autonomic regulation in patients with obstructive sleep apnea (OSA) showing periodic limb movements in sleep (PLMS) emerging after therapy with continuous positive airway pressure (CPAP). Methods Data of patients with OSA undergoing a first polysomnography for diagnosis and a second polysomnography for therapy with CPAP were reviewed. Patients with OSA showing PLMS on the first polysomnography were excluded. By using heart rate variability analysis, epochs without any sleep events and continuous effects from the second polysomnography were retrospectively analyzed. Results Of 125 eligible patients, 30 with PLMS after therapy with CPAP (PLMS group) and 30 not showing PLMS on both polysomnography (non-PLMS group) were randomly selected for the analysis. No significant differences in the demographic characteristics and variables of polysomnographies were identified between the groups. Although one trend of low root mean square of successive differences (RMSSD) between intervals of adjacent normal heart beats (NN intervals) in the PLMS group was observed, patients in the PLMS group had significantly low normalized high-frequency (n-HF) and high-frequency (HF) values, but high normalized low frequency (n-LF) and high ratio of LF to HF (LF/HF ratio). After adjustment for confounding variables, PLMS on the second polysomnography was significantly associated with RMSSD (beta = -6.7587, p = 0.0338), n-LF (beta = 0.0907, p = 0.0148), n-HF (beta = -0.0895, p = 0.0163), log LF/HF ratio (beta = 0.4923, p = 0.0090), and log HF (beta = -0.6134, p = 0.0199). Conclusions Patients with OSA showing PLMS emerging after therapy with CPAP may have a basal sympathetic predominance with potential negativecardiovascular effects.