Background/Aims: The risk for colonoscopic postpolypectomy bleeding (PPB) in patients with chronic liver disease (CLD) remains unclear. We determined the incidence and risk factors for colonoscopic PPB in patients with CLD, especially those with liver cirrhosis. Methods: We retrospectively reviewed the medical records of patients with CLD who underwent colonoscopic polypectomy at Seoul National University Hospital between 2011 and 2014. The study endpoints were immediate and delayed PPB. Results: A total of 1,267 consecutive patients with CLD were included in the study. Immediate PPB occurred significantly more often in the Child-Pugh (CP) B or C cirrhosis group (17.5%) than in the CP-A (6.3%) and chronic hepatitis (4.6%) groups (p<0.001). Moreover, the incidence of delayed PPB in the CP-B or C cirrhosis group (4.4%) was significantly higher than that in the CP-A (0.7%) and chronic hepatitis (0.2%) groups (p<0.001). The independent risk factors for immediate PPB were CP-B or C cirrhosis (p=0.011), a platelet count <50,000/μL (p<0.001), 3 or more polyps (p=0.017), endoscopic mucosal resection or submucosal dissection (p<0.001), and polypectomy performed by trainees (p<0.001). The independent risk factors for delayed PPB were CP-B or C cirrhosis (p=0.009), and polyps >10 mm in size (p=0.010). Conclusions: Patients with CP-B or C cirrhosis had an increased risk for bleeding following colonoscopic polypectomy.

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Series Elastic Actuators (SEA) have been in development for multiple decades. In spite of this, few design guidelines exist and stiffness selection for the compliant element still remains a trial-and-error process. In this paper, we experimentally validated the unlumped model first proposed by Orekhov for Rotary SEA (RSEA) and outlined a design methodology for selecting the spring stiffness based on the open loop force control bandwidth of unlumped model for series elastic actuators. We modified the unlumped model to apply to Rotary SEAs. Through experimental system identification, we demonstrated that our new unlumped model for RSEA is a valid model of actuator dynamics. Additionally, we recommended design guidelines for RSEA to achieve desired force control bandwidth based on the pure torque source assumption. An example of the design process was given and actuator performance was verified through dynamic simulations in ADAMS.

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Series Elastic Actuators (SEA) are one of the most widely studied compliant actuators in anthropomorphic robots and prostheses. However, due to the nature of its unique configuration, an unavoidable trade-off has to be made between compliance and bandwidth performance. In this paper, we show that by adopting a hypocycloid mechanism in rotary actuator designs, compliance and high force control bandwidth can be achieved at the same time, while reaping all the benefits of energy storage and shock absorption characteristics of mechanical springs.