Análise do escoamento pulsátil em fístula arteriovenosa com variação do ângulo de anastomose in vitro e in silico

Abstract

Arteriovenous Fistula (AVF) is a direct connection between an arterial and a venous vessel used as a vascular access (AV) for patients undergoing Hemodialysis (HD). The preparation of AVF causes non-physiological conditions of blood flow, inducing disturbances in the flow such as recirculation zones, stagnation points, high and low shear stress levels. These disorders are associated with the development of pathologies that promote stenosis in the vessel, which can compromise blood flow or even the loss of AVF. In order to analyze these disturbances with the variation of the Anastomosis Angle (AA), an experimental bench was built to provide pulsatile flow in AVF models. Pressure sensors MPU5050DP, digital flow sensors Type Turbine, diaphragm pump S-60-12 and microprocessors Arduino UNO, Arduino Nano and ESP32 were used. FAV were modeled with AA of 30 °, 45 °, 60 °, 75 °, 90 °, 105 °, 120 °, 135 ° and 150 °. Piezometric Lines (LP) were drawn to indicate the energy dissipated in the anastomosis. Using the Fused Deposition Modeling (FDM) technique, in vitro FAV models were manufactured by 3D printing. Using block technique, in silico FAV models were discretized into structured meshes. The pressure profile obtained on the bench proved to be equivalent to the blood pressure pulse. No structural collapse and leakage of AVF in vitro was observed for pressures between 0 to 45 kPa (337.53 mmHg). In in vitro AVF experiments, the pressure differential decreased with increasing AA, varying from 12.0 kPa to 3.1 kPa. The piezometric line indicates that the anastomosis is responsible for most of the dissipated energy. Simulations in FAV in silico result in a velocity field with a stagnation point in the external vein wall for FAV with AA of 30 °. Separation point and recirculation zone in the internal vein wall for FAV with AA of 30 °, 45 °, 60 °, 75 °, 90 ° and 105 °, these disturbances are not observed in FAV with AA of 120 °, 135 ° and 150 °. All AA have regions with high and low levels of wall shear stress (𝜏𝑤). Regions with 𝜏𝑤 above 40 Pa are present at the anastomotic junction and at the beginning of the venous segment. Shear stress below 0.4 Pa is present on the internal wall of the vein and on the opposite side the anastomotic junction in the artery. It is concluded that the FAV with AA of 120 ° and 135 ° provided lower values in the pressure differential, lower values of energy dissipated in the anastomosis and smaller variations between the pressure load and the piezometric line. FAVs with AA of 120 ° and 135 ° have smaller areas with high 𝜏𝑤 and smaller areas with low 𝜏𝑤. In this context, the AAs of 120 °, 135 ° and 150 ° appear to be the most favorable for the construction of the Arteriovenous Fistula.