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