Objective: To evaluate and quantify in vitro dimensional changes of ameroid ring constrictors (ARCs) with and without the outer stainless steel ring in place over time.
Sample population: 12 ARCs (5.0-mm diameter).
Procedures: 6 ARCs were immersed in canine plasma baths for 34 days without the stainless steel outer ring in place (group N), and 6 ARCs were immersed in canine plasma baths with the stainless steel outer ring in place (group R). The ARCs were digitally imaged at day 0, daily for the first 10 days, then on days 14, 20, 27, and 34. Inner diameter, outer diameter, luminal area, and height were measured for each time point. Volume and weight of rings were obtained at the start and completion of the study.
Results: The inner diameter, outer diameter, and luminal area were significantly different between the 2 groups over the course of 34 days. The inner diameter and luminal area of the R-group constructs did not change significantly, while the inner diameter, outer diameter, luminal area, and height of N-group constructs all significantly increased over the course of the study.
Conclusions and clinical relevance: R-group constructs had insignificant centripetal swelling without ring closure, whereas N-group constructs had significant generalized centrifugal expansion. Results of this study indicated that the outer stainless steel ring of an ARC may not be necessary for attenuation and closure of some single extrahepatic portosystemic shunts.