Phasic flow patterns at a hemodialysis venous anastomosis.

Area of Science:

• Biomedical Engineering
• Fluid Dynamics
• Vascular Surgery

Background:

• Arteriovenous hemodialysis access loops (AVLG) are vital for patients requiring long-term dialysis.
• Understanding the hemodynamics at the venous anastomosis is critical for preventing graft failure.
• Previous studies have not fully elucidated the complex flow dynamics within AVLG anastomoses.

Purpose of the Study:

• To conduct a detailed phase-by-phase analysis of local flow patterns at the venous anastomosis of an AVLG.
• To visualize and characterize flow separation, stagnation, and retrograde flow phenomena.
• To provide insights into the biomechanical factors influencing AVLG performance.

Main Methods:

• Utilized an elastic, transparent Silastic in vitro flow model replicating canine AVLG geometry.
• Employed a mock pulsatile flow loop system simulating physiological conditions.
• Performed flow visualization using laser illumination and a high-speed cine camera.

Main Results:

• Identified a distinct flow separation region downstream of the anastomotic toe.
• Observed an oscillating stagnation region along the opposite vessel wall.
• Documented particle accumulation, large swirls, double-helical patterns, and oscillating retrograde flow in the distal vein.

Conclusions:

• The venous anastomosis of AVLG exhibits complex, dynamic flow patterns including separation and stagnation.
• These flow characteristics, particularly retrograde flow, may contribute to graft complications.
• The findings highlight the importance of geometric and hemodynamic factors in AVLG design and function.