( ( By ( constricting ( the ( blood vessels ) ) ) ) ( , ( cold ( ( decreases ( swelling ( by ( ( inhibiting ( blood flow ) ) ( to ( the ( injured area ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN By) (S (VP (VBG constricting) (NP (DT the) (NN blood) (NNS vessels))))) (, ,) (NP (JJ cold)) (VP (VBZ decreases) (S (VP (VBG swelling) (PP (IN by) (S (VP (VBG inhibiting) (NP (NN blood) (NN flow)) (PP (TO to) (NP (DT the) (JJ injured) (NN area))))))))) (. .)))
By constricting the blood vessels, cold decreases swelling by inhibiting blood flow to the injured area.
(ROOT (S (NP (NNP Blood)) (VP (VBP flow) (VP (VB decrease) (SBAR (WHADVP (WRB when)) (S (NP (NN blood) (NNS vessels)) (VP (VBP constrict)))))) (. .)))