Humming Breathing and Autonomic Regulation: A Preliminary Study of Resonance Frequency and Vibratory Mechanisms

This study aimed to determine whether the effects of humming breathing (Bhramari Pranayama) on the autonomic nervous system were caused by vibratory sounds or specific respiratory patterns. Twenty-four healthy adults participated in four randomized sessions (rest, deep breathing, humming breathing, and calm humming breathing) completed over five consecutive days. Humming involved a vocalized "mm" sound, while calm humming additionally used noise-canceling earphones for auditory occlusion. Heart rate variability (HRV) was measured, and respiration-related indices were estimated from HRV-derived respiratory sinus arrhythmia patterns. Visual analog scale (VAS) responses were collected for stress, anxiety, confidence, and relaxation. Humming and calm humming breathing produced significantly slower and more stable breathing patterns than rest and deep breathing, with respiratory frequency clustering near 0.1 Hz. Day-to-day respiratory variability was lower during humming-based breathing than during rest and deep breathing. As respiratory frequency converged toward ~ 0.1 Hz, regulated breathing conditions showed an overall pattern of increased HRV compared with rest, including higher root mean square of successive differences (RMSSD), standard deviation of normal-to-normal intervals (SDNN), total power (TP), and low-frequency (LF) power. No significant differences were observed between humming and calm humming breathing for respiratory or HRV measures. The VAS analysis revealed no significant differences across the breathing conditions. The effects of humming breathing appear to be associated with the 0.1 Hz resonance frequency induced by extended exhalation rather than the vibratory sound itself. Humming breathing, which does not require a biofeedback device, may serve as a practical alternative to cyclic breathing.