Search for a command to run...
To measure the increase in outflow resistance of the SIBS microshunt when sutures of differing lengths, sizes, and materials partially occlude the lumen. In-vitro experiment The SIBS microshunt proximal end was connected to a gravity perfusion system. The distal tip was submerged below the surface within a fluid filled covered collection-beaker. Microshunt flow was quantified through collection-beaker mass changes. Each 5-minute trial was replicated four times per condition in each of five different microshunts. Various sutures were inserted into the distal end of the microshunt’s lumen and outflow resistance was measured in partly occluded states (4mm or 8mm suture length inserted, 9-0 or 10-0 suture diameters, Vicryl or nylon suture). Perfusion pressures (15, 20, or 25mmHg), were set by adjusting the reservoir height to 20.4, 27.2 and 33.4cmH20 respectively. The 4mm 10-0 nylon condition was repeated with sutures from different lots to investigate the effects of suture manufacturing variability. Outflow resistance Resistance of non-occluded SIBS microshunts (n=5) was 1.74±0.06mmHg/μl/min, matching the theoretical value of 1.76mmHg/μl/min from the Hagen-Poiseuille formula. Partial occlusion with a 4mm 10-0 suture increased resistance to 3.42±0.13mmHg/μl/min for nylon and 3.55±0.13 for Vicryl. Partial occlusion with an 8mm 10-0 suture increased resistance to 4.66±0.21 for nylon and 5.08±0.23 for Vicryl. Partial occlusion with a 4mm 9-0 suture increased resistance to 5.11±0.28 for nylon and 5.00±0.27 for Vicryl. Partial occlusion with an 8mm 9-0 suture increased resistance to 7.24±0.37 for nylon and 7.87±0.55 for Vicryl. Resistance differed significantly between non-occluded vs all partially occluded states (p<0.0001), 4 vs. 8mm partially occlusion lengths (p<0.0001), 10-0 vs. 9-0 suture diameters (p<0.0001), and 4mm 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). Non-occluded microshunt resistance as measured by the perfusion model matched theoretical values. Partial occlusion with either suture material caused substantial increases in resistance, depending on suture diameter and length, compared to non-occluded microshunts. If desired, partial occlusion with 4mm 9-0 nylon or 8mm 10-0 nylon suture is recommended, producing resistance consistently above the hypotony threshold while maintaining optimal therapeutic efficacy.