flow ▁levels ▁increase ▁seems ▁to ▁depend ▁on ▁the ▁sever ity ▁of ▁the ▁injury . ▁Sub gl ott al ▁pressure , ▁the ▁air ▁pressure ▁that ▁is ▁available ▁below ▁the ▁gl ott is ▁and ▁in ▁the ▁tra che a ▁to ▁produce ▁speech , ▁may ▁be ▁increased ▁as ▁well . ▁ ▁C aus es ▁ ▁V ocal ▁fol d ▁nod ules ▁are ▁thought ▁to ▁be ▁the ▁result ▁of ▁vocal ▁fol d ▁t issue ▁tra uma ▁caused ▁by ▁excess ive ▁mechanical ▁stress . ▁During ▁ph on ation , ▁the ▁vocal ▁fol ds ▁under go ▁many ▁forms ▁of ▁mechanical ▁stress . ▁One ▁example ▁of ▁such ▁stress ▁is ▁the ▁impact ▁stress ▁caused ▁by ▁the ▁collision ▁between ▁the ▁left ▁and ▁right ▁vocal ▁fol d ▁surfaces ▁during ▁v ibration . ▁This ▁stress ▁is ▁thought ▁to ▁reach ▁its ▁maximum ▁in ▁the ▁mid - m emb ran ous ▁region ▁of ▁the ▁vocal ▁fol ds , ▁at ▁the ▁j unction ▁of ▁the ▁anterior ▁ 1 / 3 rd ▁and ▁posterior ▁ 2 / 3 rd , ▁the ▁most ▁common ▁site ▁of ▁nod ule ▁formation . ▁V ocal ▁over use ▁( spe aking ▁for ▁long ▁periods ), ▁ab use ▁( y elling ), ▁or ▁mis use ▁( hyper function ) ▁may ▁produce ▁excess ive ▁amounts ▁of ▁mechanical ▁stress ▁by ▁increasing ▁the ▁rate ▁and / or ▁force ▁with ▁which ▁the ▁vocal ▁fol ds ▁col lide . ▁This ▁may ▁lead ▁to ▁tra uma ▁that ▁is ▁foc al ized ▁to ▁the ▁mid - m emb ran ous ▁vocal ▁fol d ▁and ▁subsequent ▁w ound ▁formation . ▁Re pe