Apnea hypopnea index or AHI rates the combination of apneas and hyponeas. Apnea relates to the airway being completely cut off for a Hyponea is a shallow breath instance where air is still being passed through partially, but is not fully obstructed.
See this recommended CPAP replacement schedule. Remember to get with your provider to see if your insurance will cover your purchase. If you do not have a durable medical provider be sure to check out Aeroflow Healthcare.