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The spectrogram shows how often the respective RR intervals (also NN intervals, the distance between two heartbeats) occur. This provides information about the proportion of sympathetic and parasympathetic heartbeats.

The spectrogram shows frequency bands from 0.04 to 0.4 Hz. The number of RR intervals of each frequency band is counted and plotted on the spectrogram. The skin-colored range shows the low RR intervals (0.04 Hz – 0.15 Hz, sympathetic range) and the purple range shows the high RR intervals (0.15 Hz – 0.4 Hz, parasympathetic range). The spectrogram is calculated using a Fast Fourier Transformation (FFT).

Simply put, with this graph, you can see how even the RR intervals are. Optimally, you have only one (or a few) distinct peak(s) in the skin-colored area and only one (or a few) distinct peak(s) in the purple area. This indicates that your RR interval repeats regularly in both the low (sympathetic) and high (parasympathetic) frequency ranges without large deviations.

Further information on the RR interval (NN interval) and the significance of the low and high frequency ranges can be found under “Explanation of the individual measured values” in this manual.

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