CPAP is a permitted assisted breathing device per FAA reg 14 - 382.41(d). US airlines must permit them aboard. To use them you need an approved battery pack.

http://www.tsa.gov/travelers/airtrav...eds/index.shtm

Travelers with Disabilities and Medical Conditions
Important Information For Our Travelers with Disabilities and Medical
Conditions

Our checkpoint security screening procedures for persons with
disabilities, medical conditions, and the mature have not changed as
a result of the current threat situation.

All disability-related equipment, aids, and devices continue to be
allowed through security checkpoints once cleared through screening.

Disability and medically related items permitted beyond the
checkpoint include:

Exterior medical devices

Assistive/adaptive equipment

CPAP machines respirators

Hearing aids

Medications and associated supplies

All diabetes related medication, equipment, and supplies

Any other disability-related equipment and associated supplies