Heart Rate Variability: Impact of Differences in Outlier Identification and Management Strategies on Common Measures in Three Clinical Populations

Abstract

Heart rate variability (HRV) is reported increasingly in pediatric research, but different strategies used to identify and manage potential outlier beats impact HRV parameter values in adults and animals. Do they in pediatrics? To compare the impact of different strategies to identifying and managing outliers, we used interbeat interval (IBI) data from three different populations: 10 stable premature infants, 33 stable pediatric oncology patients, and 15 healthy adults. Five commonly reported HRV parameters were compared using three identification and two management strategies to filter potential outliers. The three populations had different resting heart rates: 155 Ϯ 9 beats per minute (bpm) in infants, 105 Ϯ 17 bpm in children, and 87 Ϯ 12 bpm in adults. All three identification strategies flagged fewer than 2% of IBIs; the threshold identification strategy, excluding IBIs denoting heart rates Ͻ30 or Ͼ300 bpm, identified significantly fewer outliers than the other two strategies and generated higher HRV parameters in all populations (p Ͻ 0.001). There were no significant differences in HRV parameters calculated by managing identified outliers by "tossing" them versus "interpolating" values. Different strategies for identifying potential outliers are associated with significant differences in HRV parameters. Pediatric researchers who report HRV should detail their outlier filtering strategies. (Pediatr Res 62: 337-342, 2007) H eart rate variability (HRV) measurements are increasingly used by researchers to describe physiology, provide prognostic information, and measure response to therapies (1). HRV is the beat-to-beat variation of the interbeat interval (IBI) of the ECG (ECG). This variability is modulated primarily by the sympathetic and parasympathetic autonomic nervous system (2-4). Methods for calculating time and frequency-domain parameters of HRV were recommended by the Task Force of the European Society of Cardiology (5) and these methods have been widely adopted (6).The SD of the IBI (SDNN) is the most widely used measure of HRV, followed by the root mean square of the difference of successive IBIs (RMSSD). Other commonly used parameters include pNN50 (the percentage of IBIs that differ by more than 50 ms from the previous IBI), and parameters from power spectral analyses based on fast Fourier transformations, particularly low frequency (LF) and high frequency (HF) power. HF oscillations (0.15-0.4 Hz) are thought to be markers of parasympathetic and particularly vagal autonomic tone. LF oscillations (0.04 -0.15 Hz) reflect sympathetic and to a lesser extent, parasympathetic tone (7).Increases in HRV parameters, up to a point, reflect adaptability, resilience and well being, while decreases in HRV reflect rigidity, poor health status and a poor prognosis in both adults and children with a wide variety of clinical conditions (8 -23). In children HRV generally increases between the birth and fourteen years of age as the autonomic nervous system matures (24,25). In adults HRV generally decreases...

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Sensitivity to mental effort and test???retest reliability of heart rate variability measures in healthy seniors

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