Fig 1.
Wavelet coefficients, Wavelet Spectrum and Hurst Parameter.
Table 1.
Clinical data and fetal heart rate characteristics of the fetuses in the Index and the Control groups. Values are expressed as mean (s.d.) or number (%).
Table 2.
Spectral analysis indices for the Index and Control groups, using adult frequency band splitting.
Table 3.
LF/HFfinterm ratios computed using frequency bands, LF ∈ [0.04, finterm] and HF ∈ [finterm, 0.40], with different finterm, in the Index and Control groups.
Table 4.
Discriminative power of LF/HFfinterm ratios computed using frequency bands, LF ∈ [0.04, finterm] and HF ∈ [finterm, 0.40], with different finterm, within the Control group.
Fig 2.
ROC curve for representative LF/HFfinterm ratios computed from ranges LF = [0.04, finterm], HF = [finterm, 0.40] with different intermediate frequencies finterm. The classical adult bands, finterm = 0.15Hz corresponds to the dark black solid line.
Table 5.
Area under the ROC curve (AUC) LF/HFfinterm ratios, computed using frequency bands, LF ∈ [0.04, finterm] and HF ∈ [finterm, 0.40], with different finterm, in the Index and Control groups. Data are expressed as mean (s.d.), p-values quantify the statistical significance against the random classifier (diagonal on the ROC curve).
Fig 3.
for superimposed to that obtained from LF/HF0.15 are found to yield equivalent performance while the former avoids the recourse to the arbitrary and irrelevant choice of the intermediate frequency finterm = 0.15Hz.
Fig 4.
Fetal heart rate BpM time series PSD.
From left to right, BpM time series, Fourier spectrum (or Power Spectral Density) and Wavelet Spectrum (Logscale Diagram (LD)), From top to bottom, example from the Index group, example from the Control group with abnormal fetal heart rate, example from the Control group with normal fetal heart rate. The power-law shaped Fourier and wavelet spectra indicate fractal dynamics, rather than frequency band-type dynamics.
Fig 5.
Wavelet and Fourier LF/HF ratios.
The LF/HF ratio measured classically using spectral analysis is compared against the LF/HF ratio computed a posteriori using Eq (5) with the Hurst exponent , estimated via the wavelet spectrum. The very satisfactory match between both LH/HF ratios is a strong evidence indicating a power-law shaped decay of the PSD of intrapartum fetal HRV time series.