Association Between Heart Rate Variability and Systemic Endothelin-1 Concentration in Normal-tension Glaucoma

PURPOSE: To investigate the association between heart rate variability (HRV) and the plasma level of endothelin-1 (ET-1) in normal-tension glaucoma (NTG). MATERIALS AND METHODS: Twenty-four patients with NTG were enrolled. Subjects with systemic diseases were excluded. All patients underwent a complete ophthalmic examination and were referred to the rheumatology department, where HRV assessment was performed. Patients were divided into two groups according to the standard deviation of normal-normal intervals (SDNN). The low heart rate variability (LHV) group consisted of patients with SDNN values in the bottom half of range of values, and the high heart rate variability (HHV) group consisted of those with SDNN values in the upper half of the range. Blood samples were assayed for ET-1 concentrations, which were compared between the LHV and HHV groups. The relationships between the ET-1 level and HRV parameters were analyzed. RESULTS: The LHV group showed significantly lower ET-1 levels compared with the HHV group (0.57 ± 1.09 versus 2.21 ± 3.56 pg/ml, respectively; p = 0.04). Among the HRV parameters, the SDNN and total power were significantly associated with the systemic level of ET-1 (ρ = 0.729, p < 0.001; ρ = 0.713, p < 0.001, respectively). CONCLUSIONS: After excluding patients with systemic diseases, the plasma ET-1 level was associated with HRV parameters in patients with NTG. These observations suggest that the relationship between autonomic dysfunction and autoregulation may play a role in the pathogenesis of NTG.