What does an apnea/hypopnea index of 1.9 mean?

AHI: Apnea hypopnea index is the number of episodes per hour that the breathing either stops or is shallow enough to cause a drop in oxygen saturation and an arousal from sleep. AHI numbers under 5 are fairly normal as most of these episodes are very brief and not remembered by a patient. Most patients with an AHI over 10 will benefit from treatment of sleep apnea.

It means: It means on average 1.9 apnea/hypopnea episodes per hour. A good number. Read more there: http://healthysleep.med.harvard.edu/sleep-apnea/diagnosing-osa/understanding-results