▁kne es ▁compress es ▁the ▁ve in ▁behind ▁the ▁kne e ▁( the ▁pop l ite al ▁ve in ) ▁and ▁the ▁low ▁hum id ity , ▁low ▁o xygen , ▁high ▁cabin ▁pressure ▁and ▁consumption ▁of ▁alco hol ▁concent rate ▁the ▁blood . ▁ ▁A ▁recent ▁study , ▁published ▁in ▁the ▁British ▁Journal ▁of ▁Ha emat ology ▁in ▁ 2 0 1 4 , ▁determined ▁which ▁groups ▁of ▁people , ▁are ▁most ▁at ▁risk ▁for ▁developing ▁a ▁cl ot ▁during ▁or ▁after ▁a ▁long ▁flight . ▁ ▁The ▁study ▁focused ▁on ▁ 8 7 5 5 ▁frequent ▁flying ▁employees ▁from ▁international ▁companies ▁and ▁organizations . ▁ ▁It ▁found ▁that ▁travel ers ▁who ▁have ▁recently ▁under g one ▁a ▁surg ical ▁procedure ▁or ▁who ▁have ▁a ▁m align ant ▁disease ▁such ▁as ▁cancer ▁or ▁who ▁are ▁pre gn ant ▁are ▁most ▁at ▁risk . ▁Pre vent ative ▁measures ▁before ▁flying ▁may ▁be ▁taken ▁in ▁these ▁at - ris k ▁groups ▁as ▁a ▁solution . ▁ ▁Pat ients ▁who ▁have ▁under g one ▁kid ney ▁trans plant ▁have ▁a ▁high ▁risk ▁of ▁developing ▁R V T ▁( about ▁ 0 . 4 % ▁to ▁ 6 %). ▁R V T ▁is ▁known ▁to ▁account ▁for ▁a ▁large ▁proportion ▁of ▁trans pl anted ▁kid ney ▁fail ures ▁due ▁to ▁technical ▁problems ▁( dam age ▁to ▁the ▁ren al ▁ve in ), ▁cl ot ting ▁dis orders , ▁di ab etes , ▁consumption ▁of ▁cic los por in ▁or ▁an ▁unknown ▁problem . ▁Pat ients ▁who