verb

delay or prevent (someone or something) by obstructing them; hinder.

the sap causes swelling which can impede breathing

hinder,obstruct,hamper,handicap,hold back,hold up,delay,interfere with,disrupt,retard,slow,slow down,brake,put a brake on,restrain,fetter,shackle,hamstring,cramp,cripple,block,check,bar,curb,stop,thwart,frustrate,balk,foil,derail,stand in the way of,stymie,foul up,screw up,scupper,bork,cumber