( ( ( The constriction ) ( of ( ( the ( smooth muscle ) ) ( surrounding ( ( ( the bronchioles ) and ) ( ( the accumulation ) ( of mucus ) ) ) ) ) ) ) ( ( ( cause ( periods ( of ( ( ( airway obstruction ) and ) ( subsequent difficulty ) ) ) ) ) ( in ( ( moving air ) ( ( ( in and ) ( -LRB- ( ( to ( a ( greater degree ) ) ) -RRB- ) ) ) ( out ( of ( the lungs ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN constriction)) (PP (IN of) (NP (NP (DT the) (JJ smooth) (NN muscle)) (VP (VBG surrounding) (NP (NP (DT the) (NNS bronchioles)) (CC and) (NP (NP (DT the) (NN accumulation)) (PP (IN of) (NP (NNS mucus))))))))) (VP (VBP cause) (NP (NP (NNS periods)) (PP (IN of) (NP (NP (JJ airway) (NN obstruction)) (CC and) (NP (JJ subsequent) (NN difficulty))))) (PP (IN in) (S (VP (VBG moving) (NP (NN air)) (PP (PP (IN in)) (CC and) (PRN (-LRB- -LRB-) (PP (TO to) (NP (DT a) (JJR greater) (NN degree))) (-RRB- -RRB-)) (PP (IN out) (PP (IN of) (NP (DT the) (NNS lungs))))))))) (. .)))
The constriction of the smooth muscle surrounding the bronchioles and the accumulation of mucus cause periods of airway obstruction and subsequent difficulty in moving air in and (to a greater degree) out of the lungs.
(ROOT (S (NP (JJ Smooth) (NN muscle)) (VP (VBZ regulates) (NP (NP (NN air) (NN flow)) (PP (IN in) (NP (NNS lungs))))) (. .)))
Smooth muscle regulates air flow in lungs.