Figure 1.

The ECG-derived sleep spectrogram. The left part of the figure shows a healthy pattern dominated by high frequency cardiopulmonary coupling (long arrow). The right part of the figure shows a potentially pathologic (“unstable”) pattern with absence of high frequency cardiopulmonary coupling, which is replaced by low frequency coupling. Note the clear separation of high frequency and low frequency coupling bands. Further, the latter has two important spectral subcomponents: broad and narrow bands that may be abnormally elevated. The short arrow (right side) identifies broad-band elevated-low frequency coupling and the arrow-head identifies narrow band elevated-low frequency coupling. Both examples are from the Cleveland Family study participants. Frq, frequency of coupled respiration and heart rate variability.