Heart Rate and Breathing Are Not Always in Phase During Resonance Frequency Breathing.

For many years it has been an axiom among practitioners of heart rate variability biofeedback that heart rate and breathing vary in phase with each other when people do resonance frequency breathing. When people breathe at the frequency of the baroreflex system, about 0.1 Hz, heart rate and blood pressure have been found to oscillate 180° out of phase, while heart rate and breathing are in phase (zero-degree phase).