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In the analysis of HRV the Nerve-Express system uses a very effective and easy to interpret visual representation of heart rhythm, called rhythmography. Rhythmography draws the time interval between each consecutive heart beat as a straight, vertical line. The longer the interval between each heartbeat (R - R), the longer the vertical line (Fig. 1)
When these lines are graphed sequentially they present a curve-specific, wave portrait of heart rhythm (Fig. 2a). Rhythmographic representation allows a great deal of information to be compressed in a simple picture. The wave portrait in Fig. 2a is composed of 448 R-R intervals of the ECG. A spectral analysis of this curve allows Nerve-Express to identify two main spectral components (Fig. 2b):
It has been found that there is a high correlation between the power of High-frequency spectrum and the tone of the Parasympathetic Nervous System (PSNS), and also between the power of Low -frequency spectrum and the tone of the Sympathetic Nervous System (SNS). This finding has been well documented in a number of medical and scientific publications and in conference reports from the American College of Cardiology, the American Heart Association, and others. Nerve-Express uses a unique algorithm, which helps to analyse peak
amplitudes in both high and low spectral frequencies and to graph the
quantitative relationship between activities of the Sympathetic and the
Parasympathetic tones.
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