70678 20191127155455.0 doi 10.1109/TBME.2017.2758925 sideral 105199 ART-2018-105199 eng Orini, M. A time-varying non-parametric methodology for assessing changes in QT variability unrelated to heart rate variability. 2018 Access copy available to the general public Unrestricted Objective: To propose and test a novel methodology to measure changes in QT interval variability (QTV) unrelated to RR interval variability (RRV) in non-stationary conditions. Methods: Time-frequency coherent and residual spectra repre- senting QTV related (QTVrRRV) and unrelated (QTVuRRV) to RRV, respectively, are estimated using time-frequency Cohen’s class distributions. The proposed approach decomposes the non- stationary output spectrum of any two-input one-output model with uncorrelated inputs into two spectra representing the information related and unrelated to one of the two inputs, respectively. An algorithm to correct for the bias of the time- frequency coherence function between QTV and RRV is proposed to provide accurate estimates of both QTVuRRV and QTVrRRV. Two simulation studies were conducted to assess the methodol- ogy in challenging non-stationary conditions and data recorded during head-up tilt in 16 healthy volunteers were analyzed. Results: In the simulation studies, QTVuRRV changes were tracked with only a minor delay due to the filtering necessary to estimate the non-stationary spectra. The correlation coefficient between theoretical and estimated patterns was > 0.92 even for extremely noisy recordings (SNR in QTV = -10dB). During head-up tilt, QTVrRRV explained the largest proportion of QTV, whereas QTVuRRV showed higher relative increase than QTV or QTVrRRV in all spectral bands (P = 0.05 for most pairwise comparisons). Conclusion: The proposed approach accurately tracks changes in QTVuRRV. Head-up tilt induced a slightly greater increase in QTVuRRV than in QTVrRRV. Significance: The proposed index QTVuRRV may represent an indirect measure of intrinsic ventricular repolarization variabil- ity, a marker of cardiac instability associated with sympathetic ventricular modulation and sudden cardiac death. info:eu-repo/semantics/openAccess All rights reserved http://www.europeana.eu/rights/rr-f/ 4.491 2018 ENGINEERING, BIOMEDICAL 11 / 80 = 0.138 2018 Q1 T1 1.256 2018 Biomedical Engineering 2018 Q1 info:eu-repo/semantics/article info:eu-repo/semantics/submittedVersion (orcid)0000-0002-1960-407X Pueyo, E. Universidad de Zaragoza (orcid)0000-0003-3434-9254 Laguna, P. Universidad de Zaragoza (orcid)0000-0003-1272-0550 Bailón, R. Universidad de Zaragoza 5008 800 Universidad de Zaragoza Dpto. Ingeniería Electrón.Com. Área Teoría Señal y Comunicac. 68, 7 (2018), 1443-1451 IEEE trans. biomed. eng. IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING 0018-9294 1521033 http://zaguan.unizar.es/record/70678/files/texto_completo.pdf Preprint 146914 http://zaguan.unizar.es/record/70678/files/texto_completo.jpg?subformat=icon icon Preprint oai:zaguan.unizar.es:70678 articulos driver 2019-11-27-15:46:54 ARTICLE