By the early 1990s, Guilleminault et al described patients who experienced sleep fragmentation and daytime sleepiness, but who did not experience the obvious apneic or hypopneic
events that caused the brief arousals that were observed.
Nevertheless, the balance of evidence does show that CPAP is more effective than are control conditions or sham CPAP at improving scores on the apnea-hypopnea index, which measures the number of apneic and hypopneic
episodes per hour of monitored sleep.
4) The apnea-hypopnea index (AHI), also known as the respiratory disturbance index, is the sum of the number of apneic and hypopneic
events per hour during sleep, and it indicates the severity of OSA.