Objective There is still a lack of literature concerning lower extremity venous hemodynamics. The interpretation of physiological order of venous emptying indicates the direction of drainage is from the most superficial to the deepest veins. Nevertheless, there is no evidence concerning the different venous systems kinetics: the deep venous network (N1), the saphenous system (N2), the tributaries network (N3). Aim of the present study is to assess these velocities and to find clues for a physical model identification. Methods Venous Doppler investigations were performed in 18 healthy subjects (mean age 25 + 5 yo, M/F 1/1) for a total of 36 lower limbs. Diameters, peak systolic velocity (PSV) and time average velocity (TAV) of the following were assessed: N1 external iliac vein (IL), common femoral vein (CFV) above the sapheno-femoral junction (SFJ), middle thigh femoral vein (MFV), popliteal vein (PV), posterior tibial vein (PTV). N2 great saphenous vein (GSV) at the SFJ, midthigh GSV (MTGSV), midleg GSV (MLGSV), small saphenous vein (SSV) at its confluence with the popliteal vein (SPJ), midleg (SSV). N3 (whatever flow detectable GSV and/or SSV tributary). The flow was elicited both by active foot dorsiflexion, (AFD) and passive manual compression/relaxation, (C/R) maneuvers. Results The detailed values have been reported in table 1. A TAV increase was demonstrated from the most superficial N3 to the progressively deeper N2 and N1 compartments (P < .0001). Inside the single compartments no statistical differences were reported among the different segments. TAV and PSV showed a direct correlation with TAV following C/R (r2 = 0.91; P < .0001) and AFD (r2=0.95; P < .0001). The comparison among TAV following C/R and AFD showed no statistically significant differences (P = NS), except in IL (P < .0005) and in N3 (P < .0005). A diameter decrease was reported from N1 to N3 (P < .0001). A direct correlation has been found among diameter and TAV both by C/R (r2 = 0,8; P < .0005) and AFD (r2 = 0.9; P < .0001). Conclusions The present investigation provides preliminary evidences of the velocity decrease from the deepest to the most superficial compartments. These data introduce the Venturi effect as potential factor in the flow aspiration from the tributary to the deeper veins. This work is to be considered preliminary. Nevertheless the reported data represent a first step toward an objective evaluation of the hemodynamics governing the lower limb drainage. Moreover, these values can constitute the basis for further investigations in pathological and post-procedural scenarios. Table. Venous networks velocities and diameters N1 N2 N3 IL CVF MCFV PV PTV SFJ MTGSV MLGSV SSV TRIBUTARY PSVC/R cm/sec 111.2 ± 46.2 111.2 ± 26.3 112.8 ± 36.9 85.5 ± 32.3 46.8 ± 24.5 36.9 ± 26.2 49.29 ± 32.5 39.7 ± 14.3 19.8 ± 7.7 11.0 ± 3.8 PSVAFD cm/sec 111.5 ± 37.2 103.9 ± 35.5 83.3 ± 27.6 83.6 ± 28.9 48.1 ± 24.1 32.0 ± 15.8 35.1 ± 23.9 29.3 ± 12.2 25.5 ± 11.2 19.2 ± 13.0 TAVC/R cm/sec 39.6 ± 16.6 41.8 ± 11.2 43.2 ± 15.0 40.1 ± 21.6 29.4 ± 19.4 18.1 ± 12.3 21.6 ± 17.4 16.8 ± 5.0 10.8 ± 3.1 5.1 ± 2.12 TAVAFD cm/sec 41.4 ± 20.8 38.9 ± 14.6 37.2 ± 21.0 30.4 ± 10.7 25.6 ± 16.7 15.2 ± 8.8 18.9 ± 8.5 14.5 ± 7.8 14.4 ± 7.2 10.7 ± 7.8 DIAM mm 13.9 ± 2.7 12.4 ± 2.8 9.7 ± 2.5 8.5 ± 2.3 4.2 ± 0.7 3.75 ± 0.8 2.78 ± 0.7 2.32 ± 0.3 2.7 ± 0.61 1.1 ± 0.3 Table options Author Disclosures: S. Gianesini: Nothing to disclose; F. Sisini: Nothing to disclose; G. di Domenico: Nothing to disclose; E. Menegatti: Nothing to disclose; M. Vannini: Nothing to disclose; P. Spath: Nothing to disclose; P. Dalla Caneva: Nothing to disclose; S. Occhionorelli: Nothing to disclose; M. Tessari: Nothing to disclose; M. Gambaccini: Nothing to disclose; P. Zamboni: Nothing to disclose.