Abstract
Linear heart rate variability (HRV) indices are dependent on the mean heart rate, which has been demonstrated in different models (from sinoatrial cells to humans). The association between nonlinear HRV indices, including those provided by recurrence plot quantitative analysis (RQA), and the mean heart rate (or the mean cardiac period, also called meanNN) has been scarcely studied. For this purpose, we analyzed RQA indices of five minute-long HRV time series obtained in the supine position and during active standing from 30 healthy subjects and 29 end-stage renal disease (ESRD) patients (before and after hemodialysis). In the supine position, ESRD patients showed shorter meanNN (i.e., faster heart rate) and decreased variability compared to healthy subjects. The healthy subjects responded to active standing by shortening the meanNN and decreasing HRV indices to reach similar values of ESRD patients. Bivariate correlations between all RQA indices and meanNN were significant in healthy subjects and ESRD after hemodialysis and for most RQA indices in ESRD patients before hemodialysis. Multiple linear regression analyses showed that RQA indices were also dependent on the position and the ESRD condition. Then, future studies should consider the association among RQA indices, meanNN, and these other factors for a correct interpretation of HRV.
Highlights
The most common cause of mortality in patients with end-stage renal disease (ESRD) are due to cardiovascular diseases [1]
All of them were treated with hemodialysis three times a week and were not prone to hemodynamic instability
The results show that all dependent variables (SDNN, determinism, trapping time, and recurrence time type 2) are explained by meanNN, the body position, and the ESRD condition, while hemodialysis had no significant contribution
Summary
The most common cause of mortality in patients with end-stage renal disease (ESRD) are due to cardiovascular diseases [1]. The main cardiovascular alterations in ESRD are fluid overload, high blood pressure, increased vascular resistance, all inducing the modification of the mechanisms that maintain functionality during the disease [2]. Patients with ESRD receiving hemodialysis have a chronic sympathetic hyperactivity that is necessary for blood pressure stability [3,4]. Such augmented sympathetic drive is related to a higher risk of mortality in ESRD [5]. The dynamical response shown by heart rate variability (HRV) offers the possibility of inferring the acute and chronic adaptability of the cardiovascular system both in healthy subjects [8] and ESRD patients [4,9,10,11]
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