Amplitude variations in electrocardiographic S and R waves during sleep

The QRS amplitudes are modified by respiration and body movements and possibly also by changes in ventricular volume. Several studies have noted variations in QRS wave forms during exercise, but few studied have examined these aspects of the ECG during sleep. This article describes three modes of QRS wave form change during sleep--abrupt and gradual changes in the mean S- and R-wave amplitudes, and patterns of short-term variations. Possible causes of these variations are listed and it is suggested that an in-depth study of them may provide information both on the characteristics of sleep and on heart function.