Nocturnal Hemodialysis Lowers Heart Rate during Sleep and Normalizes Its Parasympathetic and Sympathetic Modulation

Abstract

Nocturnal hemodialysis (NHD)[8 hrs, 6/week] is a novel renal replacement therapy that lowers daytime blood pressure and plasma norepinephrine and corrects uremic related sleep apnea. Our aim was to test the hypothesis that NHD would lower sympathetic modulation of sino-atrial node discharge during sleep as assessed by power spectral analysis of heart rate variability (HRV). We conducted a case-control study comprising 9 patients (age: 44 ± 2)[mean ± SEM] before and after conversion from conventional hemodialysis (CHD)[4 hrs,3/week] to NHD and 10 normal subjects (age: 45 ± 3). Overnight polysomnography was used to assess heart rate, sleep stages and episodes of apnea and hypopnea per hour of sleep. Fast Fourier transformation was employed to compute frequency domain analysis of HRV (low frequency (LF)[0.05–0.15Hz] and high frequency (HF)[0.15–0.5Hz] power) during stage 2 non rapid eye movement sleep. LF/LF + HF, HF/HF + LF and LF/HF were used to estimate sympathetic and vagal modulation of heart rate and their ratio respectively. While on CHD, each subject was examined twice (1 day prior to and same night of CHD session). After conversion to NHD, each patient was studied once, on a non-dialysis night. Frequency of apnea and hypopnea decreased significantly after conversion from CHD to NHD (from 29.2 ± 9.9 to 7.2 ± 3.3 episodes per hour, p = 0.04). Subjects RR interval (ms) HF LF/HF+LF HF/HF+LF LF/HF a:p < 0.05 compared to normal controls, b:p < 0.05 compared to NHD Normal 1027 ± 44 6726 ± 4556 0.42 ± 0.04 0.42 ± 0.05 0.71 ± 0.11 CHD-1 day prior 776 ± 53a 100 ± 45a,b 0.60 ± 0.08 0.14 ± 0.02a,b 2.17 ± 0.54a,b CHD- same day 746 ± 38a 48 ± 15a,b 0.59 ± 0.10 0.17 ± 0.05a,b 3.57 ± 1.81a NHD 916 ± 67 712 ± 256 0.39 ± 0.06 0.32 ± 0.07 0.75 ± 0.22 Compared to normal subjects, CHD patients had diminished RR interval and HF spectral power. Both variables increased significantly after conversion to NHD. The ratio of LF/HF indicated significant greater sympathetic modulation of HRV in patients undergoing CHD. Normalization of this ratio occurred after conversion to NHD. Vagal modulation of heart rate is decreased during sleep in end-stage renal disease patients, causing sympathetic modulation to predominate. These abnormalities of autonomic regulation during sleep are restored towards normal by NHD. Two potential mechanisms for this are removal of a sympatho-excitatory stimulus from the uremic kidney, and a reduction in sympathetic surges caused by apnea during sleep.