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