Biomedical subjects

William Durfee

Publications and source records attributed to William Durfee.

4 recordsLinked to original sources

PubMed2004

Systematic evaluation of ureteral access sheaths.

OBJECTIVES: To compare the physical characteristics of ureteral access sheaths that affect their ability to resist buckling and kinking in the ureter. METHODS: Eight commercially available ureteral sheaths were tested. The buckling pressure was measured by adding sequential loads to a point 20 cm from the tip of the sheath until the mass that resulted in buckling of the catheter was determined. The kinking pressure was determined by measuring the diameter of the sheath with a digital caliper as sequential loads were applied to the surface of the sheath. The frictional properties of the sheath were measured by testing the force required to push the sheath through a mock tube. RESULTS: The Cook Flexor was more resistant to buckling, requiring 202 g of force before buckling occurred, and both the Cook Flexor and the Applied access sheaths were more lubricious. The kinking measurements demonstrated a linear loss of diameter of the sheath with added loads. The Applied Forte XE and Cook Flexor ureteral access sheaths were more resistant to kinking than were the other sheaths tested. CONCLUSIONS: Understanding the physical characteristics of ureteral sheaths may help determine which sheaths will perform well with regard to buckling during insertion and kinking during use.

Equipment Design↗

PubMed2004

Physical properties of flexible ureteroscopes: implications for clinical practice.

BACKGROUND AND PURPOSE: Physical characteristics may be important in the performance of a flexible ureteroscope. This study evaluated the strength of the shaft and deflection mechanism of several instruments. MATERIALS AND METHODS: Sequential loads were placed along the axis of downward deflection to measure the stiffness of the shaft and strength of deflection. Bending pressure was defined as the force required to deflect the tip of the ureteroscope 15 degrees from baseline. Buckling pressure was defined as the force that resulted in catastrophic bending (>90 degrees) of the shaft of the ureteroscope. Strength of deflection was defined as the force that resulted in loss of 10 degrees of active deflection. RESULTS: Bending pressures were lower for the Olympus URF-P3 (6.4 g) and Wolf 7325.172 (6.0 g) ureteroscopes. Similarly, buckling pressures were lower for these two ureteroscopes (9.0 g and 11.6 g, respectively). The Wolf and Storz flexible ureteroscopes had stronger deflection mechanisms than the Olympus URF-P3 and the ACMI DUR-8. CONCLUSIONS: This study demonstrates significant differences in ureteroscope strength. Higher buckling pressures may facilitate advancement of a ureteroscope over a guidewire but may impede secondary deflection. Lower bending pressures may facilitate passive intrarenal manipulation. Strength of deflection may impact the ability to maintain deflection with an instrument in the working channel.

Equipment Design↗

PubMed2004

Forearm compression by laparoscopic hand-assist devices.

BACKGROUND AND PURPOSE: Laparoscopic hand-assist devices have facilitated the broad application and acceptance of laparoscopy in urology and other surgical fields. This study evaluated forearm compression by these devices. MATERIALS AND METHODS: Five commercially available hand-assist devices were tested (Gelport, Intromit, PneumoSleeve, Handport, LapDisc). In three surgeons using a porcine model, compressive forces were measured along the paths of the median and ulnar nerves at the point of maximum proximal forearm circumference using FlexiForce A101 sensors. Glove size for all three surgeons was 7 1/2; however, the maximum forearm circumference ranged from 26 to 33 cm. The hand-assist devices were placed in pigs after skin and fascial incision (9 cm), and the insufflation pressure was set at 18 mm Hg. Surgeons subjectively rated the ease of device insertion and hand insertion, degree of forearm compression, and the development of paresthesias. RESULTS: The LapDisc was rated superior with regard to insertion. The Gelport was rated superior for hand insertion and removal; however, moderate to severe forearm compression and paresthesias were reported. The maximum forearm compression forces were highest with the LapDisc (97 mm Hg) and the Gelport (78 mm Hg) and lowest with the Handport (33 mm Hg). CONCLUSION: The choice of hand-assist device is dependent on its ease of use, efficacy at maintaining insufflation, and effect on the surgeon's performance and fatigue. The impact of forearm compression should be considered in the selection of the hand-assist device and in the development of new devices.

Animals↗

PubMed2003

Preliminary evaluation of a controlled-brake orthosis for FES-aided gait.

A hybrid functional-electrical stimulation (FES) gait system that incorporates a computer-controlled orthosis system has been developed to address the problems of rapid muscle fatigue and poor movement control that are characteristic of FES-aided gait. The orthosis is a long-leg brace that contains controllable friction brakes at both hip and knee joints. The system achieves desirable limb trajectories by utilizing the stimulated muscles as a source of unregulated power and regulating the power at each joint by computer control of the friction brakes. Muscle fatigue is reduced by locking the controllable brakes to provide the isometric joint torques necessary during stance. The hybrid gait system was evaluated and compared to conventional four channel FES-aided gait using four subjects with paraplegia. The results demonstrated significant reduction in muscle fatigue and improvement in trajectory control when using the orthosis combined with FES compared to using FES alone. Results for distance and speed improvements varied across subjects. Considerable work remains in the design of the hardware before the system is feasible for use outside the laboratory.

Adult↗