The funnel shaped occlusion balloon seals {HEAD ~ the walls} of the vessel to establish {TAIL ~ retrograde flow} of blood 
The funnel shaped occlusion balloon seals { HEAD ~ the walls } of the vessel to establish { TAIL ~ retrograde flow } of blood
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH