Comparison of Autonomic Response to Orthostatic Challenge before Hemodiafiltration in Patients with Different Intradialytic Blood Pressure Profiles

Background: The heart rate variability (HRV) response to active standing (AS) has shown preserved autonomic modulation in maintenance hemodiafiltration (HDF) patients. The aim was to compare the HRV response to AS before HDF between patients with different profiles of intradialytic systolic blood pressure (SBP). Methods: We included 55 HDF sessions from 26 patients (age 40 ± 13 years, 62% were women, and five had diabetes). Using linear regression analysis, the SBP intradialytic profile was classified into three groups: decreased SBP, increased SBP, or unchanged SBP. HRV indices were obtained during the supine position and AS. The mean values were compared by ANOVA for repeated measures, p value < 0.05 was considered significant. Results: Age, comorbidity, total ultrafiltration volume, initial SBP, and final SBP were similar between groups. In both positions, the HRV indices were similar between groups (Table 1). Although all groups had a response to AS of faster mean heart rate and lower variability (pNN50), only the group with decreased SBP responded to AS by increasing the low-frequency (LF) power and decreasing the high-frequency (HF) power. Conclusion: The autonomic response to an active orthostatic challenge before HDF shows a preserved sympathetic increase and parasympathetic decrease only in those patients who had an intradialytic SBP decrease in the subsequent HDF session. Table 1. HRV indices grouped by intradialytic SBP response. - HRV indices Decreased SBP(n = 28) Increased SBP(n = 15) Unchanged SBP(n = 12) Supine position Heart rate (bpm) 71.4 ± 7.8 * 70.4 ± 8.7 * 67.0 ± 8.7 * SDNN (ms) 298 ± 172 449 ± 283 * 475 ± 245 * pNN50 (%) 24.4 ± 22.1 * 33.6 ± 27.6 * 36.9 ± 25.1 * LF (n.u.) 64.2 ± 23.1 * 72.1 ± 20.4 73.8 ± 22.7 HF (n.u.) 36.1 ± 23.0 * 29.8 ± 16.7 28.2 ± 21.6 Log (LF/HF) 0.34 ± 0.56 0.46 ± 0.46 0.50 ± 0.55 Active standing Heart rate (bpm) 77.0 ± 11.3 76.3 ± 7.1 72.5 ± 7.9 SDNN (ms) 275 ± 127 299 ± 118 312 ± 108 pNN50 (%) 14.2 ± 15.5 20.7 ± 20.6 19.6 ± 16.8 LF (n.u.) 75.7 ± 15.2 70.7 ± 20.1 63.0 ± 19.5 HF (n.u.) 25.3 ± 15.5 29.3 ± 20.1 37.0 ± 19.5 Log (LF/HF) 0.56 ± 0.40 0.47 ± 0.47 0.27 ± 0.42 * p < 0.05 compared to active standing