Complexity Measures of Heart-Rate Variability in Amyotrophic Lateral Sclerosis with Alternative Pulmonary Capacities

Figures

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  Figure 1. The multi taper method (MTM) power spectrum of a time series of 1000 RR intervals in experimental subject (FVC < 50%). sMTM was the area beneath the spectrum but above the baseline formed by broadband noise as signal becomes chaotic. High spectral entropy (hsEntropy) and high spectral detrended fluctuation analysis (hsDFA) were derived by applying Shannon entropy and DFA functions to MTM power spectrum. Parameters for MTM power spectra were set at (i) sampling frequency, 1 Hz; (ii) time bandwidth for Discrete Prolate Spheroidal Sequences (DPSS), 3; (iii) Fast Fourier Transform (FFT) length, 256; (iv) Thomson’s “adaptive” nonlinear combination method to combine individual spectral estimates.

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  Figure 2. Values of chaotic forward parameters (CFP1 to CFP7) for control (FVC > 50%) and experimental (FVC < 50%) subjects with 1000 RR intervals. Point closest to zero, minimum; point farthest away, maximum. Point next closest to zero, 5th percentile; point next farthest away, 95th percentile. Boundary of box closest to zero, 25th percentile; line within box, median; boundary of box farthest from zero, 75th percentile. Difference between these points, interquartile range (IQR). Whiskers (or error bars) above and below box, 90th and 10th percentiles, respectively.

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  Figure 3. Box-and-whiskers plot for Higuchi fractal dimension of RR intervals of control (left: n = 29 with FVC > 50%) and experimental (right: n = 28 with FVC < 50%) subjects calculated multiple times from 10 to 150 in equidistant units for different levels of Kmax. Saturation point achieved at Kmax 40 (Figure 4). Point closest to zero, minimum; point farthest away, maximum. Point next closest to zero, 5th percentile; and point next farthest away, 95th percentile. Boundary of box closest to zero, 25th percentile; line within box, median; boundary of box farthest from zero, 75th percentile. Difference between these points, interquartile range (IQR). Whiskers (or error bars) above and below box, 90th and 10th percentiles, respectively.

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  Figure 4. uANOVA1 for Higuchi fractal dimension at varying levels of Kmax between 10 and 150 at equidistant intervals of 10. Data control set had FVC > 50% (n = 29) and experimental dataset had FVC < 50% (n = 28). The lowest p value and hence the greatest significance was accomplished for Kmax 40 (p ≈ 0.15, ≈ 15%).