Analysis of heart rate variations during sleep: presence of a newly observed non-periodic trapezoidal waveform

Heart rate variations (HRV) and ST-segment amplitude were monitored during 24-hour Holter recording in 50 patients without evidence of heart disease. Periodic fluctuations in HR were analyzed by power spectrum methods with prior removal of slow nonperiodic HR variations. In addition, a specially written algorithm was used to detect nonperiodic episodes of increased HR. These were observed mainly at night and had a typical trapezoid-like shape. The following changes were observed at night: decrease in HR, total variability, power of midfrequency range; increase in low-and high-frequency power, number of nonperiodic episodes and ST elevation. These changes at night are explained by varying degrees of sympathetic and parasympathetic activities of the autonomic nervous system.<
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