The gas delivery begins when the machine senses an effort by the patient, or the negative pressure of an inspiratory breath. A positive pressure breath is then delivered to the patient. If IPPB is used to treat atelectasis, the clinician must titrate the pressure to reach a desired tidal volume. When a certain preset pressure is reached, the machine cycles off, returning the pressure to zero. IPPB does not deliver a positive pressure during exhalation.
Pressure is negative at the beginning of inhalation.
Machine triggers a positive pressure breath. IPPB does not deliver positive expiratory pressure. IPPB is expensive and complicated to use. At no time does the pressure drop below zero. Pressure in the system decreases during inhalation but is still positive and helps to splint open the airways and re-inflate collapsed alveoli.