A flow generator coupled to {HEAD ~ a gas delivery system} delivers breathable gas to {TAIL ~ the patients airway} 
A flow generator coupled to { HEAD ~ a gas delivery system } delivers breathable gas to { TAIL ~ the patients airway }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL