An observational study of skier compliance with posted "slow" signs and ski patrollers.

OBJECTIVES: To examine the efficacy of "slow" signs and patroller presence at "slow" signs to reduce speeds of snowsports participants, compared to a condition where no sign or patroller are present, independent of other factors that may contribute to skier slowing (such as prior knowledge, trail convergence, etc.). DESIGN AND METHODS: Snowsports participant speeds were measured on "more difficult" trails using a radar gun at two ski areas with: (1) no-sign - the usual condition for the trail, and (2) slow-sign - a large "slow" sign was posted in the middle of the trail. At one ski area, a third condition was also tested: (3) slow+patroller - a ski patroller stood at the slow sign. Participant equipment type and estimated ability were also recorded. RESULTS: At one ski area, there was no significant difference in speed between conditions. At the second ski area, the differences in mean (SD) speeds were small but significant for the no-sign, slow-sign, and slow+patroller conditions: 10.9 (3.0), 10.3 (2.9), and 9.8 (2.6)m/s. Effects were driven by non-beginner skiers; on average, beginner skiers and all snowboarders were slower than non-beginner skiers and did not adjust their speed in response to the signage conditions. CONCLUSIONS: Reductions in speed for the slow-sign and slow+patroller conditions compared to the no-sign condition were small (0.5 and 1.1m/s) compared to the variation in chosen skier speed reported in other studies. The small differences in chosen speeds make it unlikely that slow sign and patroller presence alone would produce meaningful reductions in collision likelihood or severity of impacts.

Method to examine how geometry affects the release and retention of alpine touring boot-binding systems.

OBJECTIVES: Develop a method to examine the effects of component geometry and force-deflection on the release process of Tech/Pin alpine touring (AT) ski boots and bindings. DESIGN AND METHODS: For seven AT boots, we measured the critical geometric dimensions of the metal inserts at the toe region of the boots. Binding geometry (including the pins and rocker arms) and the force-angular deflection curves of typical AT bindings were measured. A kinematic model was derived to predict the contact force between the metal inserts of the AT boots and the pins of the AT bindings, dependent on angular displacement of the binding rocker arms. By combining the kinematic model, the force-angular deflection curves, and moment equilibrium, we determined the force and binding rotation angle needed to release the AT boot in a direction normal to the ski. RESULTS: The metal AT boot insert geometry and AT binding pin geometry and dimensions can affect significantly the contact states and kinematics of release. Two load-deflection curves of similar peak loads can result in significantly different maximal forces and angles to release the binding, even when the geometry and dimensions of the binding pins and boot inserts remain unchanged. CONCLUSIONS: The geometry and dimensions of the binding (pins and rocker arm) and the boot inserts define the kinematics of the binding release. The model can be used to test the effects of varying parameters on the release and retention characteristics of Tech/Pin boot-binding systems to optimize the release and retention characteristics.

Examining ski area padding for head and neck injury mitigation.

OBJECTIVES: The injury mitigation capabilities of foam, ski-area padding was examined for headfirst impacts. DESIGN AND METHODS: A custom-made pendulum impactor system was constructed using an instrumented, partial 50th-percentile-male Hybrid-III anthropomorphic testing device (ATD). For each test, the ATD was raised 1.0m, released, and swung into a 20-cm diameter wooden pole. Test trials were conducted with the wooden pole covered by ski area padding (five conditions of various foam types and thicknesses) or unpadded. Linear (linear acceleration and HIC15) and angular (angular velocity, angular acceleration, and BrIC) kinematics were examined and used to estimate the likelihood of severe brain injury. Cervical spine loads were compared to the injury assessment reference values for serious injury. Further tests were conducted to examine the changes produced by the addition of a snowsport helmet. RESULTS: 38 test trials were recorded with a mean (±sd) impact speed of 4.2 (±0.03) m/s. Head, resultant linear acceleration, HIC15, and associated injury likelihoods were tempered by ski area padding at the impact speed tested. Ski area padding did not reduce brain injury likelihood from rotational kinematics (p>0.05 for all comparisons) or reduce the cervical spine compression below injury assessment reference values. The addition of a helmet did not reduce significantly the likelihoods of brain or cervical spine injury. CONCLUSIONS: At the impact speed tested, ski area padding provided limited impact protection for the head (for linear kinematics) but did not protect against severe brain injuries due to rotational kinematics or serious cervical spine injuries.

Use of a covered stent modification to produce a transcatheter valve: laboratory and animal testing.

Stent-based transcatheter valves continue to require large sheaths inappropriate for deployment in children. Low-profile covered stent valves (CSVs) were constructed by removing triangular sections from two sides of partially expanded Palmaz P308 stents before covering the stents with 0.1 mm polytetrafluoroethylene. Valves were carefully crimped onto balloon catheters and deployed in a pulsatile flow loop. With fixed afterload and pump output, flow, degree of stenosis, effect on pulse pressure, and ease of deployment were determined for each valve. In vivo transcatheter feasibility studies were then performed by disabling the aortic valve of two 25-kg pigs, and deploying transcatheter CSVs into their descending aorta. All transcatheter valves deployed consistently via sheaths three French sizes larger than the recommended sheath for their balloon and none created significant obstruction. With the bicuspid and supravalvar CSVs, the flow was 64% and 79% (respectively) of a commercially available valve. Angiograms revealed excellent acute CSV function after deployment with only mild regurgitation and without significant obstruction to systolic flow. Although long-term testing is required, a modified CSV design may have utility in low-profile pediatric transcatheter valve replacement.

Thin film nitinol covered stents: design and animal testing.

Interventionalists in many specialties have the need for improved, low profile covered stents. Thin films of nitinol (<5-10 microns) could be used to improve current covered stent technology. A "hot target" sputter deposition technique was used to create thin films of nitinol for this study. Covered stents were created from commercially available balloon-inflatable and self-expanding stents. Stents were deployed in a laboratory flow loop and in four swine. Uncovered stent portions served as controls. Postmortem examinations were performed 2-6 weeks after implantation. In short-term testing, thin film nitinol covered stents deployed in the arterial circulation showed no intimal proliferation and were easily removed from the arterial wall postmortem. Scanning electron microscopy showed a thin layer of endothelial cells on the thin film, which covered the entire film by 3 weeks. By contrast, significant neointimal hyperplasia occurred on the luminal side of stents deployed in the venous circulation. Extremely low-profile covered stents can be manufactured using thin films of nitinol. Although long-term studies are needed, thin film nitinol may allow for the development of low-profile, nonthrombogenic covered stents.

A thin film nitinol heart valve.

In order to create a less thrombogenic heart valve with improved longevity, a prosthetic heart valve was developed using thin film nitinol (NiTi). A "butterfly" valve was constructed using a single, elliptical piece of thin film NiTi and a scaffold made from Teflon tubing and NiTi wire. Flow tests and pressure readings across the valve were performed in vitro in a pulsatile flow loop. Bio-corrosion experiments were conducted on untreated and passivated thin film nitinol. To determine the material's in vivo biocompatibility, thin film nitinol was implanted in pigs using stents covered with thin film NiTi. Flow rates and pressure tracings across the valve were comparable to those through a commercially available 19 mm Perimount Edwards tissue valve. No signs of corrosion were present on thin film nitinol samples after immersion in Hank's solution for one month. Finally, organ and tissue samples explanted from four pigs at 2, 3, 4, and 6 weeks after thin film NiTi implantation appeared without disease, and the thin film nitinol itself was without thrombus formation. Although long term testing is still necessary, thin film NiTi may be very well suited for use in artificial heart valves.