Comparison of linear and non-linear analysis of heart rate variability in sedated cardiac surgery patients

Abstract

Abstract-Heart rate variability (HRV) provides a noninvasive method to monitor functioning of the autonomous nervous system. HRV has been proposed as a potential tool for objective assessment of the level of sedation in critical care. In this paper we studied whether different linear and non-linear analysis methods may discriminate different levels of sedation in cardiac surgery patients. In addition we studied the interrelationships between the different parameters. The results show that HRV is modified by changes in the level of sedation, and that it is not completely recovered by the next day after the cardiac surgery. Both linear time and frequency domain parameters, and non-linear parameters discriminate the different levels, but especially the method based on Poincare plot analysis seems promising. As different parameters are closely correlated, a sub-set of parameters may be sufficient in the quantification of HRV in sedation.Keywords: Heart rate variability, level of sedation, intensive care, Poincare plot, entropy. I. INTRODUCTIONHeart rate variability (HRV) provides a non-invasive marker of the functioning of the autonomous nervous system (ANS). It is well known that the status of the ANS is modified by anaesthetic or sedative drugs, and that noxious stimulus causes sympathetic activation. Hence, HRV has been proposed as a possible measure of anaesthetic depth [1,2] or level of sedation [3,4].Traditionally, HRV has been quantified by linear timedomain measures such as standard deviation (SD) and root mean square of the successive R-R-intervals (RMSSD), or by spectral analysis of the HRV power in low frequency (LF, around 0.04-0.15Hz) and high frequency (HF, around 0.15.0.4Hz) bands [5]. However, ANS is not a linear system and it has been argued that non-linear analysis would be more optimal for HRV. Furthermore, there is no agreement, which parameters would be the most optimal for the analysis of HRV during anaesthesia or sedation. The objectives of this study were to: 1) study whether different linear and non-linear HRV measures may discriminate different levels of sedation in cardiac surgery patients; and 2) compare different linear and non-linear HRV measures in their performance and interrelationships with the sama data. II. METHODS A. Patients and protocolThe study was approved by the local Ethics committee of Kuopio University Hospital. All patients gave written informed consent. 26 patients scheduled for elective coronary artery bypass grafting surgery were included in the study. Anaesthesia regime (propofol-alfentanil) and postoperative sedation (propofol) were standardised.Data were recorded from patients in five different situations: 1) baseline; 2) pre-medication; 3) after cardiac surgery at intensive care unit at deep sedation (Ramsay score 6 [6]); 4) in intensive care in moderate sedation (Ramsay score 4); 5) post-operatively (the next day). B. Data acquisition and signal processingStandard patient monitor (CS/3 monitor, Datex-Ohmeda, Instrumentarium Corporation, Helsinki, Finland)) was us...

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“…In the frequency domain, high frequency (HF: 0.15–0.40 Hz) power spectral density was measured, which has also been used as an index of vagal activity and reflects primarily parasympathetic influences (15). Since the ANS is not a linear system, it has been argued that non-linear analysis would be informative for HRV (33) and nonlinear measures have also been proposed to be more accurate at predicting cardiac dysfunction, including ventricular tachycardia and sudden cardiac death (34, 35) when compared to traditional time and frequency domain analyses. Poincare analyses are commonly used as a nonlinear measures of HRV (36), including SD1, which represents a measure of rapid changes in R–R intervals.…”

Heart rate variability analysed by Poincaré plot in patients with metabolic syndrome

“…These parameters can be very useful, due to the previously mentioned combination of advantages such as the easy calculation of statistical time domain parameters [12], lesser sensitivity to non-stationarity in the signal being measured, and the ability to provide information similar to the commonly used frequency domain parameters [8].…”

“…Heart rate variability (HRV) is considered to be an important parameter in studies focused on the evaluation of autonomic nervous system (ANS) function and dysfunction [1][2][3][4][5][6][7][8]. It reflects not only the function of the ANS as a whole, but also the function of its individual parts -i.e.…”

Métodos lineares e não-lineares de análise de dados cronobiológicos de Melipona quadrifasciata (Hymenoptera, Meliponini)

“…Métodos não-lineares de análise são amplamente utilizados para dados cardiovasculares, por exemplo (e.g., Brennan et al, 2001;Korhonen et al, 2001), área na qual já se verificaram vantagens em seu emprego em detrimento de métodos lineares.…”

“…É sabido que, para sistemas não-lineares como a atividade do Sistema Nervoso Autônomo, apesar de as análises lineares serem funcionais, os métodos não-lineares descrevem melhor seu comportamento (Korhonen et al, 2001). Sendo assim, esperava-se, com as técnicas aqui empregadas, detectar padrões ou outros comportamentos eventualmente presentes nos dados, o que não ocorreu em todos os casos.…”