Maturation of the Autonomic Nervous System in Premature Infants: Estimating Development Based on Heart-Rate Variability Analysis

Figures

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  Figure 1. Visual representation of the three windowing schemes applied in this study: post-bradycardia scheme (PB), between-bradycardia scheme (BB) and within-bradycardia scheme (WB). The selected windows in each trace are indicated with gray dashed boxes, while the dot-dashed boxes show examples of annotated bradycardia. In case of BB windowing, a period T greater that 10 min is present between the end of the bradycardia and the first available window.

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  Figure 2. The block diagram shows the main steps of the study. For each RR signal, artifact preprocessing is performed and associated resampling of the tachogram. The signal is split in different windows according to the scheme of Figure 1. For each of these epochs, temporal, spectral and fractal features undergo a grand-median process if there is more than one epoch per scheme. The three datasets are then used to estimate the age of the recording in a linear mixed effects (LME) regression.

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  Figure 3. (A–J) The figure shows the linear-mixed effect regressions between the post-menstrual age and the following HRV features: the standard deviation of the tachogram σRR, the absolute and the relative power in the LF band (log10(LF),LFLF+VLF), the Hurst exponent Hexp, [j1,j2=5,12] and the parameter C2. The sampling frequencies for the fractal indices is fs = 8 Hz. The left column—magenta circles report the results for the bradycardia epochs, while the right column—indigo diamonds the results for the between-bradycardia epochs. ρ is the correlation coefficient with the associated significance pvalue.

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  Figure 4. (A–F) The figure shows results for the linear-mixed effect regression that models the relationship between Hexp, [j1,j2=5,12] and VLFLF in the first row and between Hexp, [j1, j2 = 3, 12] and LFHF in the second row. The three columns, respectively represents bradycardia epochs (magenta circle data points), post-bradycardia epochs (light-blue squares data points), and between-bradycardia epochs (indigo diamonds data points). ρ is the correlation coefficient of the regression and pvalue represents the significance of the correlation.