Investigating the relationship between fetus EEG, respiratory, and blood pressure signals during maturation using wavelet transform

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Abstract
In this study, we introduce the fast wavelet transform as a method for characterizing maturational changes in electrocortical activity, respiratory activity, and blood pressure in fetal lambs in early (110–122 days), mid (123–135 days), and late (136–144 days) third trimester (term 145 days). Each recording was 2 hr in duration. Wavelet decomposition was performed for six sets of parametersD 2j where 1≤j≤6. The six series wavelet transforms represent the following signal frequency bands: 1. 16–32 Hz; 2. 8–16 Hz; 3. 4–8 Hz; 4. 2–4 Hz; 5. 1–2 Hz; 6. 0.5–1 Hz. In the early group, power in the electrocephalogram (EEG) was highest in the fourth wavelet band, with relatively low power in the other bands. Increase in gestational age was characterized by increased power in all four wavelet bands. Power in the first wavelet band was significantly increased during low-voltage fast activity (LVFA) in the late group. The respiratory and blood pressure signals showed common frequency components with respect to time and were coincident with the LVFA EEG signal. Respiratory activity was only observed during some of the LVFA periods and was completely absent during high-voltage slow activity (HVSA) EEG. The respiratory signal showed dominant power in the fourth wavelet band, and less power in the third and fifth band. The blood pressure signal was also characterized by dominant power in the fourth wavelet band. This power was significantly increased during periods of respiratory activity. These results suggest a strong relationship between fetal EEG, blood pressure, and breathing movements.