Sleep and wake state have different influences on a variety of recordable signals that make up the polysomnogram. Conventional sleep stages are dependent on analysis of electroencephalogram (EEG) waveforms. Non-EEG approaches can provide a different view of sleep. One such example is the electrocardiogram (ECG) derived sleep spectrogram, which computes the coupling and coherence of heart rate variability and respiratory tidal volume influences on the ECG R wave. Novel insights into sleep physiology and pathology are available through this technique.