Flow visualization study of a novel respiratory assist catheter.

Respiratory assist using intravenous catheters may be a potential therapy for patients with acute and acute-on-chronic lung failure. An important design constraint is respiratory catheter size, and new strategies are needed that enable size reduction while maintaining adequate gas exchange. Our group is currently developing a percutaneous respiratory assist catheter (PRAC) that uses a rotating bundle of hollow fiber membranes to enhance CO(2) removal and O(2) supply with increasing bundle rotation rate. In this study, particle image velocimetry (PIV) was used to analyze the fluid flow patterns and velocity fields surrounding the rotating fiber bundle of the PRAC. The goal of the study was to assess the rotational flow patterns within the context of the gas exchange enhancement that occurs with increasing fiber bundle rotation. A PRAC prototype was placed in a 1-in. internal diameter test section of an in vitro flow loop designed specifically for PIV studies. The rotation rate of the PRAC was varied between 500 and 7000 rpm, and PIV was used to determine the velocity fields in the primary (r-theta) and secondary (r-z) flow planes. The secondary flow exhibited time-varying and incoherent vortices that were consistent with the classical Taylor vortices expected for Taylor numbers (Ta) corresponding to the rotation speeds studied (2200 < Ta < 31 000). In the primary flow, the tangential velocity exhibited boundary layers of less than (1/2) mm adjacent to the fiber bundle and vessel wall. The estimated shear stress associated with the Taylor vortices was approximately 11 dyne/cm(2) at 7000 rpm and was over 10 times smaller than the shear stress in the primary flow boundary layers.