Efficiency of Air Bubble Removal in Preparation of Low-Profile Angioplasty Balloon Catheter: Bench-Top Comparison of Six Methods

Impact of residual air trap in balloon on laser treatment of tubular tissue

OBJECTIVES

Tubular tissue, such as the bile duct and esophagus, often suffers from stenosis due to chronic inflammation or excessive contraction of smooth muscle. Laser treatment using a balloon catheter has been used to treat tubular tissue stenosis by mechanically expanding the tissue and irradiating laser light circumferentially on the tissue lumen. As the balloon is inflated with saline, the residual air in a delivery channel is often accumulated in the inflated balloon. Thus, the air trap may cause physical discontinuities at air-saline interface, leading to unpredictable and nonuniform photothermal interactions. The aim of the current study was to evaluate the optical-thermal effects of the air trap in the balloon on laser treatment of the tubular tissue by means of numerical simulations and experimental validations.

MATERIALS AND METHODS

A balloon-assisted diffusing applicator (BDA) was developed to inflate a balloon and deliver uniform and circumferential laser light. Before the balloon inflation, various numbers of deflations (0, 1, 2, 3, and 4) were applied to estimate the average amount of the air removed from the balloon. Ex vivo experiments using porcine liver duct were conducted with two deflation conditions (D0: no deflation for air trap and D3: three deflations for no air trap). The balloon was horizontally situated during laser irradiation to maintain the air trap at the same position in the balloon by minimizing gravity effect. Upon balloon inflation, 532 nm laser light was delivered through the BDA to the tissue (irradiance = 4 W/cm² ) at 10 W for 45 seconds to assess the optical-thermal effects of the air trap on the ductal tissue.

RESULTS

The size of the air trap was noticeably reduced with the number of deflations. The air trap volume in the balloon decreased to 0.5% of the total balloon volume after D3. Ex vivo results demonstrated that thicker coagulative necrosis (CN) for D0 near the air trap region in the tissue than bottom region that contact with saline, representing an asymmetric profile of CN in the tissue. D0 generated 17% thicker and nonuniform CN (overall CN thickness = 1.4 ± 0.7 mm), compared with D3 with no air trap (overall CN thickness = 1.2 ± 0.2 mm; p < 0.05). A threefold larger eccentricity (E) was found in D0 (49 ± 31%) than D3 (15 ± 13%; p < 0.001).

CONCLUSION

Both numerical simulations and experiments validated the effect of the air trap in a balloon on the distribution of CN in a tubular tissue during BDA-assisted laser treatment. Further in vivo studies will assess the current findings on the air trap for clinical translations of BDA-assisted laser treatment of tubular tissue stenosis.

Preparation of PCI Balloons: What Is the Best Method to Avoid Air in the Balloon? A Comparison of Different Methods of Connecting PCI Balloons and the Inflation Syringe while Removing Air from the Balloon

As the techniques to connect percutaneous coronary intervention (PCI) balloons and the inflation syringe vary in the instructions for use and in practice, we measured the amount of air in PCI balloons after testing three connection methods to an inflation syringe. Following the preparation using one of the three methods, 114 balloons and stent balloons were tested four times. Method 1 connected the syringe and the balloon catheter directly after purging and filling the lumen, while method 3 omitted the purging and filling process. With method 2, the catheter lumen was purged, filled and fully vented via a three-way valve. The primary endpoint answered whether air remained in the balloon, and if so, the secondary endpoint indicated the total volume of remaining air. The connection with a three-way valve achieved significantly less air in the inflated balloon as compared with either direct connection approach (27% vs. 44% and 51%; p = 0.015). For the direct connection, no significant difference between purging and filling the lumen prior to making the connection or not existed. According to these findings, the best method to connect a PCI balloon to the inflation syringe while removing air involves using a three-way valve.