Biomedical subjects

D W Ilsley

Publications and source records attributed to D W Ilsley.

3 recordsLinked to original sources

PubMed1996

The effects of isolation on the mechanics of the human heel pad.

In previous studies on the mechanical properties of the human heel pad (Bennett & Ker, 1990; Aerts et al. 1995) the fat pad and part of the calcaneus was removed from amputated test specimens. The present study tested whether this procedure influences the mechanical behaviour of the sample. Intact amputated feet were therefore mounted on steel rods driven through the calcaneus and placed in a mechanical test situation (pendulum or servohydraulic material tester). The mechanical properties of the pad were determined for a series of experiments in which the pad was gradually freed from the foot in the way done by Bennett & Ker (1990) and Aerts et al. (1995). The results showed no observable differences in the mechanics of the pad by isolating it from the rest of the foot. Thus, in relation to human locomotion, the load-deformation relation of heel pads as described by Aerts et al. (1995) is the most appropriate to date.

Adult↗

PubMed1995

The mechanical properties of the human heel pad: a paradox resolved.

In vivo and in vitro mechanical testing of the human heel pad gave apparently different properties for this structure: the in vivo stiffness is about six times lower, whereas the percentage of energy dissipation is about three times higher (up to 95% loss). It was postulated that this divergence must be ascribed to the lower leg being involved in in vivo heel pad testing. This hypothesis is presently evaluated by applying the two experimental procedures formerly used in the in vivo (an instrumented pendulum) and in vitro (an Instron servo-hydraulic testing machine) investigations on the same isolated heel pad samples. Instron load-deformation cycles mimicking pendulum impacts (i.e. 'first loop-half cycles') are first evaluated and then compared to real pendulum impacts. When performed properly, the pendulum test procedure reveals the same mechanics for isolated heel pads as the Instron does. The load-deformation loops are basically identical. Thus similar non-linear stiffnesses (about 900 kN m-1 at body weight) and comparable amounts of energy dissipation (46.5-65.5%) are found with both types of test, still being largely different from the former in vivo results (150 kN m-1 and 95%, respectively). Therefore, the present findings support the hypothesis that the presence of the entire lower leg in in vivo tests indeed influences the outcome of the measurements. It must be concluded that the previously published in vivo data, if interpreted for the heel pad alone, implied not only an incorrectly low resilience but also a value far too low for stiffness.

Adult↗

PubMed1994

The cold hemiplegic arm.

BACKGROUND AND PURPOSE: Vasomotor changes occur in the arm after hemiplegic stroke. Previous studies have provided conflicting results, with most showing an increase in skin temperature of the hemiplegic arm. However, a number of patients complain of distressing coldness of the hemiplegic arm. METHODS: Eleven patients with symptomatic coldness and 10 patients with hemiplegia but no coldness were recruited. The severity of the symptom of coldness was compared by questionnaire with other common symptoms after stroke. A thermographic camera was used to record the finger skin temperature response to cold stress. Blood flow to both hands was also measured simultaneously by means of two plethysmographs. In all patients there were no symptoms in the unaffected arm, and this was used as a control. RESULTS: The symptom of coldness rated highly compared with other symptoms. In the symptomatic group the finger temperature on the hemiplegic side was lower at rest (median difference at rest, 0.65 degrees C; P < .0001) and at all times after cold stress. In the asymptomatic group the fingers on the hemiplegic side were colder at rest and after initial cooling (median temperature difference, 0.2 degrees C) but at no other time. Hand blood flow on the hemiplegic side was also decreased in the symptomatic group by 35%. This was not seen in the asymptomatic group. CONCLUSIONS: Coldness of the hand may be a severe and distressing symptom in some patients after hemiplegia. Symptomatic patients have lower finger skin temperatures at rest and after standard cold stress. These symptomatic patients also had reduced blood flow to the hemiplegic hand.

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