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BiLevel positive airway pressure (BiLevel) machines have two different pressures; a higher pressure when breathing in and a lower pressure when breathing out. By alternating the inhalation and exhalation pressures, the BiLevel encourages the lungs to operate more efficiently.
Most BiLevel machines work by switching between the two air pressures in response to your breathing. This is known as spontaneous BiLevel. However, patients with more complicated pulmonary disorders (chronic obstructive pulmonary disease, emphysema, etc.) may require the machine to set the respiratory rate through either a backup rate or a timed rate. Most BiLevel machines can deliver up to 30 cm H2O.