FLOW VISUALIZATION STUDY OF A PULSATING RESPIRATORY ASSIST CATHETER

Abstract

The Hattler Catheter® is an intravenous respiratory assist device that uses a centrally located pulsatile balloon within a hollow fiber bundle to enhance gas exchange by active blood mixing. Flow visualization techniques were used to investigate flow patterns induced by balloon pulsation in this respiratory catheter. We tested the hypothesis that the nonsymmetric inflation and deflation of the balloon leads to nonuniform balloon-generated perfusion of the fiber bundle. The respiratory catheter was placed in a 1“ ID rigid test section of an in-vitro test loop (3 L/min DI water). Particle image velocimetry (PIV) was used to map the velocity vector field arising from balloon pulsation at 120 beats/min. in lateral cross-sections of the test vessel. Velocity measurement showed that radial velocity varied between 5 cm/s in the region adjacent to the top and bottom quarters of the fiber bundle and 0 cm/s in the region adjacent to the right and left quarter of fiber bundle. We hypothesized that the nonuniform radial flow caused by nonsymmetrical balloon collapse would lead to different gas exchange in the affected fiber regions. An in-vitro study of local gas exchange was performed by selectively perfusing sweep gas flow (100% helium) to four quarter regions of the fiber bundle. Preliminary results showed 15–45% variation in CO2 exchange among these regions. The variation was not only attributed to nonuniform radial velocities, but also visual observations of nonuniform fiber motion around the bundle. Quantification of fiber motion, via PIV, will be pursued to analyze the relative velocity.