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. During exhalation, the positive expiratory pressure provides PEP therapy to further splint the airways. Pressure is positive during inspiration.
Pressure is positive during the breath hold.
Pressure is positive during exhalation.