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Effect of an Intraluminal Suture on Outflow Resistance in an in Vitro Styrene-Block-Isobutylene-Block-Styrene
William J Herspiegel1, James J Armstrong2, Anastasiya Vinokurtseva2
1Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada.
Purpose:
Measure outflow resistance of the styrene-block-isobutylene-block-styrene (SIBS) microshunt when sutures of differing lengths, sizes, and materials partially occlude the lumen.
Design:
In vitro experiment METHODS: The SIBS microshunt proximal end was connected to a gravity perfusion system. The distal tip was submerged within a fluid-filled covered collection-beaker. Microshunt flow was quantified through collection-beaker mass changes. Each 5-minute trial was replicated 4 times per condition. Various sutures were inserted into the distal end of the microshunt's lumen, and outflow resistance was measured in partly occluded states (4-mm or 8-mm suture length inserted, 9-0 or 10-0 suture diameters, Vicryl or nylon suture). The 4-mm 10-0 nylon condition was repeated with sutures from different lots to investigate the effects of suture manufacturing variability.
Main Outcome Measure:
Outflow resistance.
Results:
Resistance of nonoccluded SIBS microshunts (n = 5) was 1.74 ± 0.06 mmHg/μl/minute, matching the theoretical 1.76 mmHg/μl/minute from the Hagen-Poiseuille formula. Partial occlusion with a 4-mm 10-0 suture increased resistance to 3.42 ± 0.13 mmHg/μl/minute for nylon and 3.55 ± 0.13 for Vicryl. Partial occlusion with an 8-mm 10-0 suture increased resistance to 4.66 ± 0.21 for nylon and 5.08 ± 0.23 for Vicryl. Partial occlusion with a 4-mm 9-0 suture increased resistance to 5.11 ± 0.28 for nylon and 5.00 ± 0.27 for Vicryl. Partial occlusion with an 8-mm 9-0 suture increased resistance to 7.24 ± 0.37 for nylon and 7.87 ± 0.55 for Vicryl. Resistance differed significantly between nonoccluded versus all partially occluded states (P < 0.0001), 4- versus 8-mm partially occlusion lengths (P < 0.0001), 10-0 versus 9-0 suture diameters (P < 0.0001), and 4-mm 10-0 nylon sutures from different lots (P < 0.0001). No difference was observed between suture materials (P > 0.05) or different microshunts (P > 0.05).
Conclusions:
Nonoccluded microshunt resistance measured by the perfusion model matched theoretical values. Partial occlusion with either suture material caused substantial resistance increases, depending on suture diameter and length, compared with nonoccluded microshunts. If desired, partial occlusion with 4-mm 9-0 nylon or 8-mm 10-0 nylon suture is recommended, producing resistance consistently above the hypotony threshold while maintaining optimal therapeutic efficacy.
Financial Disclosure(S):
Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.
