Method of presenting audible and visual cues for synchronizing the breathing cycle with an external timing reference for purposes of synchronizing the heart rate variability cycle with the breathing cycle

A method of presenting audible and visual cues to a human for synchronizing a breathing cycle with an external timing reference for purposes of synchronizing a heart rate variability cycle with the breathing cycle, thereby achieving coherence of the heart rate variability cycle, comprising:

• a) generating a human perceptible indication to identify inhalation phases and exhalation phases of the breathing cycle, changes between said inhalation and exhalation phases, progression of said inhalation and exhalation phases in time, and progression of said inhalation phases and exhalation phases relative to a period of time having a combination of the inhalation phases and exhalation phases, the combination having a center frequency, wherein the period of time having the center frequency represents a nominal heart rate variability cycle and generating the human perceptible indication of the progression of the inhalation phases and the exhalation phases employs frequency modulation as the basis of the progression;
• and
• b) instructing the human to align the breathing cycle with the generated human perceptible indication to synchronize the heart rate variability cycle with the breathing cycle to achieve coherence of the heart rate variability cycle.