Heart rate variability and slow-paced breathing: when coherence meets resonance

Clinical research on the beneficial effects induced by slow-paced breathing has been increasingly extended in the past twenty years. Improvements in cardiovascular functioning, executive functions, or stress management appear to be among the most prominent observations in these studies. However, the mechanisms underlying these effects are multiple and complex. This review will focus on the importance of reducing breathing rate at the resonant frequency (~ 0.1 Hz), which increases cardiac oscillations, thus reflecting improved vagally-mediated heart rate variability and baroreflex sensitivity. These effects are achieved through temporal coherence of respiratory, blood pressure, and cardiac phases, which are the origin of multiple peripheral benefits. In return, vagal afferents, which send inputs to interoceptive areas, are stimulated for longer and more intensely than when breathing spontaneously. In limbic areas, which may also be stimulated through larger cerebral blood flow oscillations and increases in oxygen delivery, interoceptive activation produces a cascade of neural activations that may be at the origin of the central benefits of deep and slow-paced breathing.