The PTP allows to visualize the equation of motion throughout the entire inspiratory cycle. When the patient is spontaneously breathing the equation is:
Where, Pm is the muscle pressure, PEEPi is the intrinsic PEEP (or AutoPEEP), Ers is the elastance of the respiratory system, V is the volume, Rrs is the resistance of the respiratory system and F is the flow.
If a PTP graph is analysed at a given moment, it can be seen how each one of the segments corresponds with one term of the equation of motion. Which is to say that the areas of the PTP is the equation of motion in time.