***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: The effect of incremental increases in external pressure , applied to the leg , on blood volume flow in the femoral vein was studied in dogs . Clinical investigation of external pressure increases was also carried out on nine patients undergoing surgery for varicose veins . An external pressure between 5 and 15 mm . Hg caused a sustained increase in mean femoral vein flow both in a control and in the compressed limb . Above 15 mm . Hg external pressure flow decreased in the compressed limb but was maintained at an increased level in the control limb . If external compression is to be used to prevent and treat deep vein thrombosis its application must be carefully controlled The LONFLIT study was planned to evaluate the incidence of deep venous thrombosis ( DVT ) occurring as a consequence of long flights . In the Lonflit 1 study 355 subjects at low-risk for DVT and 389 at high-risk were studied . Low-risk subjects had no cardiovascular disease and used no drugs . All flights were in economy class . The average flight duration was 12.4 hours ( range , 10 - 15 hr ) . The mean age of the studied subjects was 46 years ( range 20 - 80 yr , SD 11 ; 56 % males ) .  DVT diagnosis was made by  ultrasound scans after the flights ( within 24 hours ) . In low-risk subjects no events were recorded while in high-risk subjects 11 had DVT ( 2.8 % ) with 13 thromboses in 11 subjects and 6 superficial thromboses ( total of 19 thrombotic events in 389 patients [ 4.9 % ] ) . In the Lonflit2 study the authors studied 833 subjects ( r and omized into 422 control subjects and 411 using below-knee stockings ) . Mean age was 44.8 years ( range , 20 - 80 yr , SD 12 ; 57 % males ) . The average flight duration was 12.4 hours . Scans were made before and after the flights . In the control group there were 4.5 % of subjects with DVT while only 0.24 % of subjects had DVT in the stockings group . The difference was significant . The incidence of DVT observed when subjects were wearing stockings was 18.75 times lower than in controls . Long-haul flights are associated to DVT in some 4 - 5 % of high-risk subjects . Below-knee stockings are beneficial in reducing the incidence of DVT The LONFLIT1 and 2 studies established that in high-risk subjects after long ( > 10 hours ) flights , the incidence of deep venous thrombosis ( DVT ) may be between 4 % and 6 % . The LONFLIT3 study aim ed to evaluate methods of prevention in high-risk subjects . Of 467 subjects contacted for the study , 300 were included . These 300 subjects at high risk for DVT were r and omized , after informed consent , into three groups : 1 ) a control group that had no prophylaxis ; 2 ) an aspirin treatment group , in which patients were treated with 400 mg , ( tablets of oral , soluble aspirin ; one dose daily for 3 days , starting 12 hours before the beginning of the flight ) ; and 3 ) a low-molecular-weight heparin ( LMWH ) group , in which one dose of enoxaparine was injected between 2 and 4 hours before the flight . The dose was weight-adjusted ( 1000 IU [ equivalent to 0.1 mL ] per 10 kg of body weight ) . Subjects with potential problems due to prophylaxis with aspirin or LMWH or at risk of drug interactions were excluded . Of the 100 included subjects in each group , a total of 249 subjects completed the study ( dropouts due to low compliance or traveling/connections problems were 17 % ) . Age and sex distribution were comparable in the three groups as well as risk distributions . Mean age was 47 ( range , 28 - 75 ; SD , 11 ; 65 % males ) . Of the 82 subjects in the control group , there were 4.82 % of subjects with DVT with two superficial thromboses . In total 4.8 % of limbs suffered a thrombotic event . Of 84 subjects in the aspirin treatment group , there were 3.6 % of patients with DVT and three superficial thrombosis . In total 3.6 % of limbs had a throm botic event . In the LMWH group ( 82 subjects ) , there were no cases of DVT . One superficial thrombosis was documented . In total only 0.6 % of limbs had a thrombotic event ( p < 0.002 in comparison with the other two groups ) . DVT was asymptomatic in 60 % of subjects ; 85 % of DVTs were observed in passengers in non-aisle seats . Mild gastrointestinal symptoms were reported in 13 % of patients taking aspirin . One dose of LMWH is an important option to consider in high-risk subjects during long-haul flights The LONFLIT1/2 studies have established that in high-risk subjects after long ( > 10 hours ) flights the incidence of deep venous thrombosis ( DVT ) is between 4 % and 6 % . The LONFLIT4 study has been planned to evaluate the control of edema and DVT in low-medium-risk subjects . The aim of this study was to evaluate edema and its control with specific flight stockings , in long-haul flights . In the first part of the study 400 subjects at low-medium risk for DVT were contacted ; 28 were excluded for several nonmedical problems ; 372 were r and omized into 2 groups to evaluate prophylaxis with stockings in 7 - 8-hour flights ; the control group had no prophylaxis . Below-knee , Scholl , Flight Socks , producing 14 - 17 mm Hg of pressure at the ankle , were used in the treatment group . The occurrence of DVT was evaluated with high-resolution ultrasound scanning ( femoral , popliteal , and tibial veins ) . Edema was assessed with a composite score based on parametric and nonparametric measurements . Part II : In this part of the study 285 subjects at low-medium risk for DVT were included and r and omized into 2 groups to evaluate edema prophylaxis in 11 - 12-hour flights ; the controls had no prophylaxis while the prevention group had below-knee , Scholl , Flight Socks ( comparable to part I ) . Results . Part I : DVT evaluation . Of the 184 included subjects in the stockings group and 188 in the control group , 358 ( 96.2 % ) completed the study . Dropouts were due to compliance or connection problems . Age/sex distributions were comparable in the groups . Stockings Group : of 179 subjects ( mean age 49 ; SD 7 ; M : F = 101:78 ) , none had DVT or superficial thromboses . Control Group : of 179 subjects ( mean age 48.4 ; SD 7.3 ; M : F = 98:81 ) , 4 ( 2.2 % ) had a DVT . There were also 2 superficial thromboses . In total , 3.35 % ( 6 ) subjects had a thrombotic event . The difference ( p < 0.002 ) is significant . Intention-to-treat analysis detects 15 failures in the control group ( 9 lost + 6 thromboses ) out of 188 subjects ( 7.9 % ) versus 5 subjects ( 2.7 % ) in the stockings group ( p < 0.05 ) . All thrombotic events were observed in passengers sitting in nonaisle seats . The tolerability of the stockings was very good and there were no complaints or side effects . Thrombotic events were asymptomatic . No difference was observed in the distribution of events between men and women . The 3 women who had a thrombotic event were taking low-dose , oral contraceptives .  Edema evaluation : The level of edema at inclusion was comparable in the 2 groups . After the flight there was a score of 6.7 ( 3.1 ) in controls ; in the stockings group the score was 2.9 times lower ( p < 0.05 ) . The control of edema with stockings was clear considering both parametric ( circumference , volume ) and nonparametric ( analogue scale lines ) data . Part II : DVT evaluation . Of the 285 included subjects , 271 ( 95 % ) completed the study . Dropouts were due to low compliance or connection problems . Age/sex distributions were comparable in the groups . Stockings Group : of 142 subjects ( mean age 48 ; SD 8 ; M : F = 89:53 ) , none had DVT or superficial thromboses . Control Group : of 143 subjects ( mean age 47 ; SD 8 ; M : F = 87:56 ) , 3 had a popliteal DVT and 3 a superficial thrombosis . In total , 4.2 % ( 6 ) subjects had a thrombotic event . The difference ( p < 0.02 ) between groups is significant . Intention-to-treat analysis detects 14 failures in the control group ( 8 lost + 6 thromboses = 9.7 % ) versus 6 ( all lost = 4.2 % in the stockings group ) ( p < 0.05 ) . Four of 6 events ( 3 DVT + 1 SVT ) were observed in non-aisle seats . The tolerability of the stockings was very good . No difference was observed in the distribution of events between men and women . Edema evaluation : The level of edema at inclusion was comparable in the 2 groups . After the flight there was a score of 8.08 ( 2.9 ) in controls while in the stockings group the score was 2.56 ( 1.5 ) ( p < 0.005 ) . In conclusion . Scholl Flight Socks are very effective in controlling edema . Also this type of compression is effective in significantly reducing the incidence of DVT and thrombotic events in low-medium-risk subjects , in long-haul flights . Conclusions : Considering these observations , Flight Socks are effective in controlling edema and in reducing the incidence of DVT in low-medium-risk subjects , in long-haul flights ( 7 - 11 hours ) The mechanisms by which graduated compression stockings prevent deep venous thrombosis are not completely understood . In the current study the physiologic effect of low-pressure graduated compression stockings on the venous blood flow in the lower limb and the practical aspects of their use were assessed . Patients having elective orthopaedic surgery at a university orthopaedic department were r and omized into five groups to wear two different types of graduated compression stockings in thigh and knee lengths . Patients in the fifth control group did not wear graduated compression stockings . Venous occlusion strain gauge plethysmography was used to measure venous flow . After 20-minutes bed rest there was a highly significant increase in venous capacitance and venous outflow in patients in all of the four groups wearing stockings . There was no difference in the mean of the percentage change of venous capacitance in patients in the four groups wearing stockings . The knee length Brevet stockings were less efficient in increasing the venous outflow . There was no significant change in the venous capacitance and venous outflow in patients in the control group . Visual assessment of the fit and use of stockings was done , and patients ’ subjective opinion of comfort was sought . The knee length graduated compression stockings  wrinkled significantly less , and significantly fewer patients reported discomfort with them . All stockings were reported to be difficult to use . Thigh and knee length stockings have a significant effect on decreasing venous stasis of the lower limb . Knee length graduated compression stockings are similarly efficient in decreasing venous stasis , but they are more comfortable to wear , and they wrinkle less OBJECTIVE to develop a model simulating factors of " long haul " flight to investigate the relationship with DVT . MATERIAL S AND METHODS volunteers ( 19 males : 20 females ) sat for 6 h in a warm ( > 25 degrees C ) , dry environment , limited in movement , consuming alcohol ( 40 ml of 40 % alcohol/hour ) and salted foods ( 300 g ) . Half of the subjects received 150 mg aspirin and wore especially design ed below-knee , compression stockings ( Class 1 profile ) . Changes in full blood counts were recorded , and as an indication of DVT formation , plasma was analysed for D-dimer . Limb swelling was assessed from leg measurements . RESULTS after 6 h , in controls , there were significant rises in platelet packing ( Pct p<0.04 ) , total platelet numbers ( p<0.003 ) and total numbers of white blood cells ( WBC 's p<0.001 ) . With aspirin plus stockings , there were similar significant rises in total platelet numbers ( p<0.002 ) and total WBC 's ( p<0.001 ) . In both groups , significant rises were seen in all WBC types ( except basophils ) . Wearing compression stockings prevented calf swelling seen in controls after 6 h ( p<0.002 ) . No subject developed a DVT , or a change in levels of D-dimer . CONCLUSION changes in the cellular components of blood , particularly WBC 's , combined with vaso-compression and reduced flow could predispose towards DVT . Aspirin , combined with compression stockings , may provide prophylaxis BACKGROUND The true frequency of deep-vein thrombosis ( DVT ) during long-haul air travel is unknown . We sought to determine the frequency of DVT in the lower limb during long-haul economy-class air travel and the effic 
    Output:
    
This review demonstrates the effectiveness of medium compression pressure , below-knee graduated compression stockings in preventing flight-related deep vein thrombosis but not superficial venous thrombosis in low-medium- or high-risk participants