According to our previous experimental results, in the venous system several physiological adaptive mechanisms can be activated by both acute and chronic orthostatic loads. Deeper knowledge of the structural and functional properties of human veins can provide support to the prevention and treatment of venous diseases. The aim of this study was to evaluate and compare the passive and active biomechanical properties of human superficial veins from the neck and the lower extremities known to be exposed to different orthostatic stress.

Methods. 

Superficial veins removed during vascular surgical procedures from the jugular and the saphenous regions were studied by digital videoangiometry. We cannulated the cilindrical vein segments at both ends and incubated them in 37C oxigenized normal Krebs-Ringer (nKR) solution at a transmural pressure of 10 mmHg. Outer and inner diameters of the vessel segments were measured using a Leica sotftware. Digitalized pressure-diameter curves were registered between 2–30 mmHg in nKR solution, then after administration of 10^­5M norepinephrine, 10^­5M acetilcholin and 10^­4M L-NAME. Calcium-free solution was used to determine the active and passive biomechanical properties of the samples. Paired t-test and Wilcoxon test were applied for statistical data analysis.

Results. 

Average outer diameter was 1518±403mm of the neck veins (n=8) and 1289±237mm of the leg segments (n=7) in nKR. We found the wall thickness to be significantly smaller in the cervical samples (89,99±12,73mm) than in the leg ones (95±11,47mm) at 10 mmHg pressure (p<0,0001). There was no significant difference in elastic modulus. Distensibility of jugular branches (0,02603±0,00463 1/mmHg) was significantly higher (p=0,0274) than that of saphenous segments (0,01328±0,0023 1/mmHg). Both spontaneous myogenic tone (0,0863±0,0296 vs. 0,1925±0,0558) and contractility (0,1224±0,0486 vs. 0,3798±0,0487) proved to be significantly smaller in the neck samples than those in the leg veins (p<0,0001).

Discussion. 

Comparing active and passive biomechanical properties of human veins affected chronicly by different orthostatic loading, we found several remarkable quantitative differences. The greater wall thickness/diameter ratio, smaller distensibility, higher spontaneous tone and contractility of the leg veins all might be important components of physiological adaptation mechanisms evolved in response to long-term gravitational stress.

(Supported by Hungarian national grants OTKA 32019 and 42670, Hungarian Kidney Foundation)