What is periodic breathing?

My leak rate is 0% and AHI is 1.8 and periodic breathing is 2%. I don't understan the periodic breathing part??????

Periodic breathing is Respironics terminology for Cheyne-Stokes Respiration.
In Cheyne-Stokes ( and I have Cheyne-Stokes about 10% of the time ), the breathing follows a pattern of increasing depth of breath until some maximum is reached and then decreasing depth of breath until a minimum is reached. The pattern is repeated for some period of time.

If you are having Central Apneas, then the minimum between cycles tends to be zero, you just stop breathing.
Unlike Obstructive Apneas where your airway is blocked and you continue to try to breath until the airway opens enough, in Cheyne-Stokes, you just stop breathing and don't even try to breathe. It's pretty scary when the minimums stretch out for 15 to 30 seconds or so.

Do a Google search for "Cheyne-Stokes" and you will get a better idea of what is going on.

It is symptom of some fairly severe medical conditions ususally but not always. Be sure to check with your sleep doc and get an opinion of what might be causing this condition.

In my case, its called idiopathic Cheyne-Stokes which means they don't have a clue as to the cause but its not one of the 'bad' ones related to heart and lungs.

Your machine supports reporting on breathing wave forms with the correct software. Getting that and having a printout to discuss with your doc will be useful.

The software is Encore PRO and if you make a request on this forum, someone will get you a link to download it.

Check with your doc to make sure all is OK.