01 Humming for ~60 seconds drives sinus resonance that vents more nasal nitric oxide (NO), with studies showing up to a 15-fold increase versus quiet breathing.
02 Bone conduction transmits hum vibrations through the skull into paranasal sinuses (maxillary, frontal, ethmoid, sphenoid), producing sustained acoustic resonance.
03 Inhaled sinus-derived NO and pulmonary vasodilation can transiently improve oxygen diffusion; humming also enforces an exhale-dominant breathing ratio (≈3:1–4:1).
04 Mechanical vibration plus the breathing pattern activate the vagus nerve through two parallel pathways, shifting autonomic balance toward parasympathetic tone.
05 Rhythmic intrathoracic pressure changes during humming may move cerebrospinal fluid and aid brain clearance, though CSF effects are more preliminary than NO and vagal evidence.