The medical literature points a special attention on the investigation of cardiac variability (HRV). It is now well established that a healthy heart offers a variability which shows some flexibility. This flexibility is reduced with aging and according to the state of the heart.

When the variation of the cardiac rhythm is recorded, we observe a curve which evolves with time. (fig. 1)


Fig. 1 : two minutes of recording of the variation of the cardiac rhythm of a resting subject.

This curve is a wave from which the various components can be analyzed by a mathematical process. In this case, we obtain a spectrum of the various frequencies components (represented according to their respective power) which compose this wave (fig. 2):

Fig.2 : decomposition of the wave representing the variation
of the cardiac rhythm in the various wavebands which define it.

The spectrum of the variability of cardiac rhythm (HRV) shows three significant wavebands respectively called HF (high frequencies), LF (low frequencies) and VLF (very low frequencies). . (references HRV1, HRV2)

  • The HF band, corresponding to frequencies ranging from 9 to 24 cycles per minute, would be mainly associated with the PARASYMPATHETIC system;
  • The LF band, corresponding to frequencies ranging from 3 to 9 cycles per minute, was initially interpreted as being associated with (ORTHO)SYMPATHETIC system; but it is now allowed that it is associated at the same time with the (ORTHO)SYMPATHETIC system and the PARASYMPATHETIC system.
  • The VLF band , which corresponds to frequencies ranging from 1 to 3 cycles per minute should be related to thermoregulation.

Currently, the measurement of these various parameters is carried out in two different ways:

  • Variations of frequency of the cardiac pulsations are recorded on a definite amount of time. Then the powers of signals associated with wavebands HF, LF and VLF are extracted (like in fig. 2)
  • The evolution of the size of various wavebands HF, LF and VLF extracted from the variation of the cardiac rhythm (cfr fig. 2) are visualised in real time.

The relative proportion of these various wavebands gives information on the stress or on the health condition of the cardiovascular system. The ratio LF/HF is often used to monitor the recovery of the heart after a heart attack (reference HRV2).

The computer interface system I propose allows the representation and visualisation IN REAL TIME of the three waves corresponding to the components HF, LF and VLF of the variations of the cardiac rhythm. This system also integrates information on breathing, allowing a direct visualisation of the impact of the respiration on these three parameters (fig. 3)


Fig 3: real time drawing of the variations of cardiac rhythm HRV (in light blue), of breathing (dark blue), HF (white),
LF (brown), and VLF (green).
Click on the picture for an animation


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