Adaptive auditory stimulation sustains auditory-respiratory coordination and promotes slowing of spontaneous breathing

Auditory feedback may influence breathing without explicit instructions to regulate it, but its precise impact remains unclear. We examined responses to adaptive and nonadaptive breath-like sounds during passive listening. Thirty-nine young adults completed four counterbalanced conditions: nonrhythmic filtered noise (Static), rhythmic sounds progressively slowing or speeding relative to initial breathing rate (Slowing and Speeding respectively), and sound adapting continuously to respiratory frequency and phase with a prescribed phase delay relative to respiration (Adaptive). Each condition included 4 min of nominal silence followed by 4 min of stimulation. Primary outcomes were breathing rate slopes, auditory–respiratory phase locking as a measure of auditory-respiratory coordination, respiratory sinus arrhythmia, and subjective relaxation. Breathing-rate trajectories differed across conditions; Adaptive showed a more negative slope than Static, although average rates were similar. Phase locking was higher and more sustained during Adaptive than during the nonadaptive rhythmic conditions. Respiratory sinus arrhythmia trajectories differed, but planned contrasts did not survive multiplicity correction. A relaxation composite score did not differ by condition, but an item-level analysis indicated less physical relaxation after Adaptive than Static. Secondary outcomes provided no evidence of increased cardiorespiratory coupling or reduced upper-trapezius muscle activity. Interestingly, the negative breathing-rate trajectories remained significantly different in Adaptive compared to Static after retaining only the 25 respondents that did not notice the sound’s adaptation to their breathing. These findings support adaptive auditory stimulation as a means of supporting auditory-respiratory coordination during uninstructed listening, with a modest and relative change in breathing rate. Clinical benefits and independence from intentional breathing control remain to be tested.