Sympathetic activation and baroreflex function during intradialytic hypertensive episodes

Abstract

Background: The mechanisms of intradialytic increases in blood pressure are not well defined. The present study was undertaken to assess the role of autonomic nervous system activation during intradialytic hypertensive episodes.

Methodology/principal findings: Continuous interbeat intervals (IBI) and systolic blood pressure (SBP) were monitored during hemodialysis in 108 chronic patients. Intradialytic hypertensive episodes defined as a period of at least 10 mmHg increase in SBP between the beginning and the end of a dialysis session or hypertension resistant to ultrafiltration occurring during or immediately after the dialysis procedure, were detected in 62 out of 113 hemodialysis sessions. SBP variability, IBI variability and baroreceptor sensitivity (BRS) in the low (LF) and high (HF) frequency ranges were assessed using the complex demodulation technique (CDM). Intradialytic hypertensive episodes were associated with an increased (n = 45) or decreased (n = 17) heart rate. The maximal blood pressure was similar in both groups. In patients with increased heart rate the increase in blood pressure was associated with marked increases in SBP and IBI variability, with suppressed BRS indices and enhanced sympatho-vagal balance. In contrast, in those with decreased heart rate, there were no significant changes in the above parameters. End-of-dialysis blood pressure in all sessions associated with hypertensive episode was significantly higher than in those without such episodes. In logistic regression analysis, predialysis BRS in the low frequency range was found to be the main predictor of intradialytic hypertension.

Conclusion/significance: Our data point to sympathetic overactivity with feed-forward blood pressure enhancement as an important mechanism of intradialytic hypertension in a significant proportion of patients. The triggers of increased sympathetic activity during hemodialysis remain to be determined. Intradialytic hypertensive episodes are associated with higher end-of-dialysis blood pressure, suggesting that intradialytic hypertension may play a role in generation of interdialytic hypertension.

Figure 1. Representative tracings of continuous recordings of SBP and IBI oscillations and variability during intradialytic hypertension episodes with decreased (A) or increased heart rate (B).

Tracings of a patient with marked intradialytic hypotension are depicted for comparison (C). The episodes associated with sudden changes in blood pressure are shown by the bolder parts of the tracings. LF, low frequency; HF, high frequency; IBI, interbeat interval.

Figure 2. SBP and interbeat interval and their variability indices before and during intradialytic hypertensive episodes associated with increased (n = 45) or decreased (n = 17) heart rate.

Data are presented as box plots. The box stretches from the 25^th to the 75^th percentile; the median is shown as a small black square in the box. The range (the upper and the lower extreme values) is indicated by whiskers. HF, high frequency; LF, low frequency, IBI, interbeat interval.

Figure 3. BRS indices and LF IBI/HF IBI ratio before and during intradialytic hypertensive episodes associated with increased (n = 45) or decreased (n = 17) heart rate.

Data are presented as box plots. The box stretches from the 25^th to the 75^th percentile; the median is shown as a small black square in the box. The range (the upper and the lower extreme values) is indicated by whiskers. BRS, baroreceptor sensitivity; HF, high frequency; LF, low frequency, IBI, interbeat interval.

Figure 4. Correlations of changes in interbeat intervals with changes in SBP during intradialytic hypertensive episodes associated with increased (n = 45) or decreased (n = 17) heart rate.

HF, high frequency; LF, low frequency, IBI, interbeat interval.