{HEAD ~ An air flow sensor} and pressure sensor is positioned to monitor {TAIL ~ air flow} channeled to the mask 
{ HEAD ~ An air flow sensor } and pressure sensor is positioned to monitor { TAIL ~ air flow } channeled to the mask
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH