The slope of the phase III is increased. This is a normal physiological variation. Airway obstruction can result in an increase in the phase III as well. Depending on the severity of airway obstruction, phase II can also be prolonged.
Occasionally, a phase IV can also occur in capnograms recorded during anesthesia in pregnant subjects.
Bhavani-Shankar et al. Canadian Journal of Anaesthesia 1992;39:617-32.
Shankar KB et al. Arterial to end-tidal carbon dioxide difference during cesarean section anaesthesia. Anaesthesia 1986;41:698-702.
Shankar KB et al. Arterial to end-tidal carbon dioxide difference during anaesthesia for tubal ligations. Anaesthesia 1987;42:482-6.