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Cardiovascular regulatory mechanisms that fail to compensate for ultrafiltration and cause hypovolemia during hemodialysis (HD) are not completely understood. This includes the interaction between the autonomic nervous system and the biochemistry that regulates blood pressure and modulates cardiac activity and vascular tone in response to hypovolemia in patients treated with HD. The objective was to evaluate the association of spectral indices of heart rate variability (HRV) with serum levels of angiotensin II, angiotensin 1–7, nitric oxide and total antioxidant capacity during HD. Electrocardiographic records were obtained from 20 patients during HD (3 h), from which HRV data and spectral power data in the very-low-frequency (VLF), low-frequency (LF) and high-frequency (HF) bands were generated. Three blood samples per patient were collected during HD (0.0, 1.5, 3.0 h) to determine the levels of biomarkers involved in the pressor response during HD. Angiotensin II had a positive correlation with VLF (r = 0.390) and with LF/HF (r = 0.359) and a negative correlation with LF (r = −0.262) and HF (r = −0.383). There were no significant correlations between HRV and the other biomarkers. These results suggest that during HD, VLF could reflect the serum levels of angiotensin II, which may be associated with the autonomic response to HD. [ABSTRACT FROM AUTHOR]

Featured Application: In this work, a spectrotemporal evaluation of heart rate variability during hemodialysis shows differences between hypotensive and non-hypotensive patients in the spectral bands related to the sympathetic and parasympathetic nervous system. This methodology could be implemented in a dedicated electronic system for the early detection of intradialytic hypotension events. Intradialytic hypotension occurs in 10–30% of hemodialysis (HD) sessions. This phenomenon affects the cardiovascular system's functions, which are reflected in the activity of the autonomic nervous system (ANS). To indirectly assess the ANS during HD, we analyzed the mean R–R intervals and the spectral power of heart rate variability (HRV) from 20 end-stage renal disease patients divided into hypotensive and non-hypotensive groups. The spectrotemporal analysis was accomplished using short-time Fourier transform with 10 min epochs of HRV overlapping by 40%. The spectral power was divided into three segments according to high frequency, low frequency, and very low frequency bandwidths and averaged to fit quadratic regression models. The analysis of the mean R–R intervals showed significant differences between the groups (p = 0.029). The power variation over time was significant in each spectral band (p ≪ 0.05). The average power, maximum power, and time when the peak was reached differed for each band and between groups, showing the ability to correctly identify the decompensation of the ANS and discriminate between hypotensive and non-hypotensive patients. Additionally, the changes in the sympathovagal ratio were not significant and very scattered for the hypotensive group (p = 0.23) compared to the non-hypotensive group, where the changes were significant (p ≪ 0.05) and much less scattered. [ABSTRACT FROM AUTHOR]

Power spectral analysis of heart rate variability (HRV) offers a possibility to non-invasively quantify autonomic cardiac regulation. The technique splits the spectrum of the HRV into high frequency (HF), low frequency (LF) and very-low frequency (VLF) bands, and relates their power content to parasympathetic outflow, sympathetic outflow, and hormonal factors as well as thermoregulation, respectively. In this work, we applied this technique on HRV data from 20 end-stage renal disease (ESRD) patients to estimate power distribution in these three bands as well as their changes respect to time during hemodiafiltration (HDF) therapy; as an indirect way to assess the modulatory activity over the cardiac system. HRV data was processed using the continuous wavelet transform (CWT), power was estimated using 5-min as well as 10-min epochs for comparison purposes, and the results were normalized to unity before linear regression analysis. For 5-min epochs, the LF power increased (p = 0.035), while there were no significant changes in the HF power (p = 0.2). In contrast, for 10-min epochs, both the LF (p = 0.002) and HF (p = 0.043) power decreased, while the VLF power increased (p<<0.05) and had larger values than the other two spectral powers. There were no statistically significant changes in the LF/HF ratio for any of the two epochs evaluated (5-min: p = 0.56, 10-min: p = 0.44). Results based on 5-min epochs are in agreement with previous studies, while those based on 10-min epochs suggest that modulatory mechanisms within the VLF band override the sympathovagal balance and play a key role in managing the cardiovascular response during hemodiafiltration. [ABSTRACT FROM AUTHOR]