BiPAPs are typically used by those with central sleep apnea
If you have trouble accepting elevated air pressures or the constant air pressure of a CPAP machine, your doctor may prescribe a BiPAP machine. It operates just like a CPAP machine in delivering air pressure during sleep, but the BiPAP features lower pressure at exhalation and provides pressure during inspiration. With a BiPAP machine, you will not feel as if you are exhaling against high pressure while breathing.
If you have difficulties exhaling or need high pressure to keep your airways open, a BiPAP machine will be best for you. Those with central sleep apnea use BiPAP machines to help them inhale and exhale. If you are curious, central sleep apnea is a rare condition caused by neurological disabilities not sending the proper signals from the brain to instruct the mouth and lungs to breath.