Aim: The aim of this study was to evaluate and compare passive and active biomechanical properties of human superficial veins exposed in vivo to different orthostatic stresses.
Methods: Superficial veins from jugular and saphenous regions were studied (11 segments each). Digitalized pressure-diameter curves were recorded in Krebs-Ringer solution, and after administration of 10-5M norepinephrine and 10-5M acetylcholine. Calcium-free solution was used to determine passive biomechanical properties. Similar tissue samples were collected for histochemistry. Resorcin-fuchsin stainings and immuno-histochemistry for smooth muscle actin were used.
Results: The outer radius of the relaxed samples was identical. Leg vein walls were thicker in Krebs-Ringer solution (110 ± 11 vs. 84 ± 7 µm at 30 mmHg). Isobaric wall stress was significantly higher in cervical veins. The significant differences in incremental distensibilities and elastic moduli were dependent on pressure level and smooth muscle tone. Spontaneous tone and norepinephrine induced contractions were significantly higher in leg veins (at 30 mmHg 18.3 ± 4.1 vs. 5.6 ± 1.8% and 37.6 ± 4.5 vs. 11.2 ± 4.3 %, respectively). Endothelial dilation was larger in cervical vein segments (3.8 ± 0.9% vs. 1.8 ± 0.5%). Resorcin-fuchsin and smooth muscle actin staining structures were more abundant in leg veins.
Conclusion: Comparing active and passive biomechanical properties of human veins affected chronically by different orthostatic loading, we found several quantitative differences that reflect the physiological adaptation mechanisms to long-term gravitational stress.