The difference between a bilevel positive airway pressure machine and a continuous positive airway pressure machine is that a BiPAP contains two pressure settings -- one for exhalation and one for inhalation -- whereas a CPAP has only one pressure setting for inhalation, explains the Alaska Sleep Education Center. A BiPAP is generally for patients with higher pressure settings.
Both a CPAP and BiPAP machine deliver pressurized air to a patient's airways via a mask to help prevent throat muscles from collapsing in individuals suffering from sleep apnea, states the Alaska Sleep Education Center. Though it may come with a ramp feature that gradually increases air pressure until it reaches a certain level at which it remains constant for the rest of the night, a CPAP machine typically delivers this pressurized air at a single consistent pressure throughout the night. Some patients may find it difficult to exhale against this pressure.
A BiPAP remedies this issue by including a breath timing feature that allows the machine to alternate between pressures, a higher one for inhalation and a smaller one for exhalation, so breathing doesn't feel difficult in certain patients, according to the Alaska Sleep Education Center. The pressure difference in a BiPAP typically begins at 4 centimeters and may exceed this number. Certain CPAP machines come with a C-flex option, which also provides a pressure drop for exhalation. A BiPAP contains a fixed pressure difference between inhalation and exhalation, whereas the C-flex varies from breath to breath. The C-flex also only provides at most 3 centimeters of pressure difference between inhalation and exhalation.