Nocturnal monitoring in the evaluation of continuous positive airway pressure

Continuous positive airway pressure (CPAP) counterbalances forces leading to upper airway narrowing or collapse during sleep and is the most widely used treatment for obstructive sleep apnea (OSA). In patients with OSA, progressively higher CPAP levels applied during sleep turn obstructive apneas into hypopneas, hypopneas into continuous inspiratory flow limitation, with or without snoring, and flow limitation into unobstructed breathing. When breathing becomes unobstructed, "respiratory arousals" (i.e., arousals that may follow increased inspiratory efforts associated with obstructed breathing) are eliminated, while sleep becomes more stable and sleep cycles more regular, contributing to improvements in subjective sleep quality, daytime sleepiness, and quality of life usually observed after just a few nights of CPAP application. Also, relief of upper airway obstruction is associated with resolution of intermittent hypoxemia and hemodynamic swings that accompany obstructive events, with a consequent reduction in long-term cardiovascular morbidity and mortality.