upper airway collapse

The throat is the one part of the breathing passage with no rigid scaffold of bone or cartilage to hold it open. Unlike the windpipe with its stiff rings, the pharynx is a muscular tube kept patent only by the active pull of surrounding muscles. Upper airway collapse is what happens when, during sleep, that muscular support fades and the soft walls of the throat fall together, narrowing or sealing the passage.

The physics is captured by a simple idea: a flexible tube collapses when the pressure inside drops below the pressure of the tissues pressing on it from outside. As we inhale, we create negative pressure inside the airway to draw air in; if the dilating muscles are too relaxed or the surrounding tissue too bulky, that suction pulls the walls inward. The level where it gives way is usually behind the soft palate or the tongue base.

Collapse is the central event of obstructive sleep apnea and underlies snoring and the upper airway resistance syndrome along a spectrum: mild narrowing causes vibration (snoring), greater narrowing causes increased breathing effort and arousals, and complete closure causes an apnea. The same anatomy that predisposes to snoring — a crowded throat, large tonsils, a set-back jaw, excess soft tissue — predisposes to collapse.

Treatments work by countering collapse in different ways: positive airway pressure pneumatically splints the tube open from inside, an oral appliance advances the jaw and tongue to widen it, side sleeping and weight loss reduce the load on it, and surgery can remove or stiffen the collapsing tissue. The level and pattern of collapse vary between people, which is why one therapy does not suit everyone.