Fig. 2
From: Distinct polysomnographic and ECG-spectrographic phenotypes embedded within obstructive sleep apnea
Sample ECG-spectrogram. Note high, low and very low frequency coupling (HFC, LFC and VLFC respectively) and the clear separation in signal space of HFC from LFC/VLFC. HFC is the ECG-spectrogram signal biomarker of stable breathing and stable sleep. VLFC reflects REM or wake