Dissection properties of human arteries

Projekt: Arbeitsgebiet



Arterial dissections may occur spontaneously or non-spontaneously and have been observed in several arterial branches. Arterial dissections frequently result from an intimal tear from a perforation of the intima as, for example, caused by intramural hemorrhage and hematoma formation. Moreover, mechanical traumatization of the intima due to cannulation for catheter-based diagnostic and therapeutic interventions have been identified as initiating arterial dissections. These intimal defects can cause concentrations of mechanical stress of the pressurized artery and may be the trigger for the propagation of the medial dissection.
Untreated, a dissection may propagate until it runs either back into the lumen, resulting in the reduplication of the arterial lumen (false lumen), or it ruptures through the adventitia, often with a lethal outcome. For example, in the absence of intervention, acute aortic dissections have a 90% chance of mortality, and the majority of these deaths occur within 48 hours.
This project was carried out with the goal to investigate the dissection properties of the arterial media, the external elastic membrane (i.e. elastic membrane between adventitia and media) and the internal elastic membrane (i.e. elastic membrane between media and intima). We conducted two different mechanical failure tests on prepared arterial specimens denoted by (i) direct tension tests and (ii) peeling tests. The direct tension test demonstrates the dissection strength across the lamellae of the media, the external elastic membrane and internal elastic membrane in the radial direction, while the peeling experiment explores the fracture energy required to propagate a dissection. A cylindrical blanking tool is used to punch out coin-shaped specimens for the direct tension test (6 mm in diameter). In the circumferential direction and in the axial direction oriented rectangular-shaped strip specimens are cut out of the artery with a surgical scalpel for the peeling tests. The mechanical study is enhanced by histology at different stages of the peeling test to explore the development of irreversible changes on the microscale level during medial dissection. In addition, histological investigation of the direct tension specimens and peeling test specimens are conducted to observe whether the specimens are dissected in the required layer.
Mechanical tests were performed on a computer-controlled, screw-driven high-precision tensile testing machine, which was adapted for small biological specimens. The specimens were investigated in a perspex container filled with 0.9% physiological saline solution maintained at 37°C by a heater-circulation unit and the tensile force were measured with a 10N class 1 strain-gauge load-cell. The upper and the lower fixing clamps of the testing machine are moving in opposite directions, which keeps the center of the specimen fixed in space. A position control resolution of 0.04 m of the upper and the lower crosshead of the tensile testing machine and a combined error of 0.03% of the 10N load cell is specified by the manufacturer.
Under certain assumptions, the performed experiments allow an estimation of the constitutive properties of an arterial dissection. This data will serve as a basic input for the finite element modeling of the experiments. From this combined experimental and numerical investigation an accurate prediction of the dissection properties are feasible.
Tatsächlicher Beginn/ -es Ende1/02/07 → …