The effects of cyclic tensile and stress-relaxation tests on porcine skin

When a living tissue is subjected to cyclic stretching, the stress-strain curves show a shift down with the increase in the number of cycles until stabilization. This phenomenon is referred to in the literature as a preconditioning and is performed to obtain repeatable and predictable measurements. Preconditioning has been routinely performed in skin tissue tests; however, its effects on the mechanical properties of the material such as viscoelastic response, tangent modulus, sensitivity to strain rate, the stress relaxation rate, etc….remain unclear. In addition, various physical interpretations of this phenomenon have been proposed and there is no general agreement on its origin at the microscopic or mesoscopic scales. The purpose of this study was to investigate the effect of the cyclical stretching and the stress-relaxation tests on the mechanical properties of the porcine skin. Cyclic uniaxial tensile tests at large and constant strain were performed on different skin samples. The change in the reaction force, and skin's tangent modulus as a function of the number of cycles, as well as the strain rate effect on the mechanical behavior of skin samples after cycling were investigated. Stress-relaxation tests were also performed on skin samples. The change in the reaction force as a function of relaxation time and the strain rate effect on the mechanical behavior of skin samples after the stress-relaxation were investigated. The mechanical behavior of a skin sample under stress-relaxation test was modeled using a combination of hyperelasticity and viscoelasticity. Overall, the results showed that the mechanical behavior of the skin was strongly influenced by cycling and stress relaxation tests. Indeed, it was observed that the skin's resistance decreased by about half for two hours of cycling; the tangent modulus degraded by nearly 30% and skin samples became insensitive to the strain rates and accumulated progressively an inelastic deformation over time during cycling. Finally, the hysteresis loops became very narrow at the end of cycling and after relaxation process.

Public-access defibrillation: where do we place the AEDs?

BACKGROUND

Many prehospital cardiac arrests occur in public places. Even the best EMS systems have a finite response time. Therefore, it has been recommended that automated external defibrillators (AEDs) be placed in public areas for immediate access by trained members of the general public.

OBJECTIVE

To determine the locations of multiple cardiac arrests in order to plan for placement of public-access AEDs.

METHODS

Retrospective review of all primary cardiac arrests in calendar year 1997. Cardiac arrests in which resuscitation was not attempted (DOA), traumatic cases, pediatric cases, and those due to "other" causes were excluded. Location of the cardiac arrest was obtained from the ambulance run ticket. The EMS system is an urban, Midwestern, all-ALS, public-utility model system with fire department first responders that transports approximately 58,000 patients annually.

RESULTS

There was scene response to 922 cardiac arrests. 377 DOAs and 219 nonprimary cardiac arrests were excluded. There were 326 primary cardiac arrests. Sixteen locations had more than one cardiac arrest: 11 locations had two cardiac arrests, four locations had three cardiac arrests, and one location had four cardiac arrests. The airport, an airline overhaul facility, a casino, and two hotels each had two cardiac arrests; the other locations of multiple cardiac arrests were in nursing homes. The professional sports stadiums had no cardiac arrests.

CONCLUSIONS

Since very few locations had more than one cardiac arrest, it may be difficult to identify high-yield public places in which to place an AED. Nursing homes may want to consider AED availability.

Intravenous torsemide as adjunctive therapy in patients with acute pulmonary edema

The safety and efficacy of intravenous (i.v.) torsemide as adjunctive therapy for acute cardiogenic pulmonary edema was evaluated. Thirteen patients were treated with i.v. torsemide and six patients, with i.v. furosemide, as a positive control. Doses of torsemide, 20 mg or 40 mg, and furosemide, 40 mg or 80 mg, were administered initially. The dose was titrated as necessary over the next 24 hours. In patients who received i.v. torsemide, median fractional sodium excretion significantly increased from 2.88% (0.04-10.1%) at baseline to 6.76% (0.71-11.6%) at peak (P = 0.0342). Hourly urine volume increased from 134 mL (25-400 mL) to 375 mL (145-790 mL) (P = 0.0034). Torsemide administration resulted in a significant improvement in both pulmonary rales and orthopnea. None of the patients experienced serious adverse events or required withdrawal from the study. These results suggest that i.v. torsemide is an effective and well-tolerated diuretic in patients with acute cardiogenic pulmonary edema.

The DCR psychology course at Stoke

This article describes the course developed at Stoke-on-Trent to cover the psychological aspect of patient care, inter-staff relationships and communication skills. Emphasis is placed on the recent developments in the content of course against a background of the continuing use of experimental learning methods. The importance of clinical experience is stressed together with the notion that students gain confidence in their own abilities by practising in a safe environment. The article is presented for the consideration of teachers engaged in this essential part of the syllabus and curriculum.