A barometer or altimeter is the classic example of an absolute pressure sensor, whereas an airspeed sensor is the classic example of a differential pressure “DP” measurement, reports Sensors Online.
Continuous positive airway pressure (CPAP) is commonly prescribed to treat sleep apnea. The machines need a differential pressure sensor to regulate flow to the user. Recently machines have even started to report statistics on when a user has an “event” which is basically a period of high resistance to flow. The Apnea-Hypopnea Index (AHI) is used to quantify sleep apnea severity.
from Sleep Review http://www.sleepreviewmag.com/2018/04/what-separates-a-differential-pressure-sensor-from-other-pressure-sensors/