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A humidifier will help a lot with the mouth breathing.

I forget why, sorry, but there is a physiological reason.

He should definitely have a humidifier. One of the nose's functions in normal breathing is to humidify the air passing through it. Cpap overstresses that normal function, and so takes too much moisture out of the nose, leaving the nose and hence the rest of the airways drier than they should be.

Di

Have him do a full blood test as erectile dysfunction is often the first sign of a more serious medical condition eg diabetes , the big C etc etc . Don't assume its apnea related