It is the Bernoulli principle, which centers on a local drop in intra-airway pressure whenever air flows at
high velocity through narrowed pipes. The faster the flow at point of constriction, the lower the local
pressure. Eventually, the drop in pressure becomes severe enough to collapse the airway. Since the
collapse also reduces flow, the airway reopens and the fluttering cycle starts anew, repeating itself indefinitely .Thus, wheezes are not produced by vibration of air (as in organ pipes or woodwind
instruments), but by vibration (fluttering) of airway walls. This is facilitated by fast jets of air, forced by
high expiratory pressures through tightly compressed airways.