Transducers for foot pressure measurement: survey of recent developments

Recent advances in the development of transducers for the measurement of vertical and shear forces acting on the plantar surface of the foot are reviewed. Barefoot and in-shoe discrete and matrix transducers are reviewed in terms of structure, operation, performance and limitations. Examples of capacitive, piezoelectric, optical, conductive and resistive types of transducer are presented. Where available, the current clinical status is specified.     

Effect of postactivation potentiation on dynamic knee extension performance

Six men and four women performed, in separate trials, maximal dynamic knee extensions with loads of 15%, 30%, 45% and 60% of maximal isometric knee extension peak torque (MVC). The dynamic extensions were done after postactivation potentiation (PAP) had been induced with a 10-s MVC, and in a control trial without PAP. PAP, measured as the increase in evoked twitch torque, was 53 (4)% (SE) and 43 (3)% at the time of the first and second extensions with each load. PAP failed to increase the attained peak velocity with any load; on the contrary, there was a trend for peak velocity to decrease in the first extension, which occurred ≅15 s after the 10-s MVC. The results suggest that fatigue produced by the 10-s MVC suppressed any benefit that could be derived from the induced PAP. A surface electromyogram (EMG) recorded from one muscle of quadriceps femoris gave no indication of activation failure in the first knee extension; however, activation impairment specific to the rate of force development cannot be ruled out. It is concluded that the strategy employed, namely of having knee extensions performed soon after the 10-s MVC to maximize PAP at the time of performance, was unsuccessful because there had been insufficient time for recovery from fatigue. It is possible that a longer recovery time, even at the cost of a diminished PAP, may have proved beneficial. Accepted: 27 July 2000     

Different effects of depolarization and muscarinic stimulation on the Ca2+/force relationship during the contraction-relaxation cycle in the guinea pig ileum

The effects of K⁺ depolarization and of the muscarinic agonist carbachol on [Ca²⁺]_i and force were investigated in smooth muscle sheets of the longitudinal layer of the ileum loaded with Fura-2. K⁺ -rich solutions increased [Ca²⁺]_i and force to an initial peak value, which was determined by the concentration of [K⁺]_o. Thereafter, [Ca²⁺]_i and force declined to a lower maintained level. The Ca²⁺/force relationship observed during this contraction-relaxation cycle is represented by a clockwise hysteresis loop. At 140 mM [K⁺]_o, this loop consisted of three components while at lower [K⁺]_o a two-component loop was observed. The stimulation with 0.1 mM carbachol resulted in a transient increase of [Ca²⁺]_i and force followed by a continuous decline of these parameters despite the presence of the drug. Its EC₅₀ of relaxation was around 270 nM [Ca²⁺]_i. The Ca²⁺/force relationship proceeded along a counterclockwise hysteresis loop during the contraction-relaxation cycle. The extent of this loop decreased but remained unaltered in its direction during repeated stimulation with carbachol. These results suggest that (a) both agonists increase force and [Ca²⁺]_i during stimulation; (b) during depolarization with K⁺, desensitization to Ca²⁺ occurs resulting in a clockwise hysteresis loop; (c) during carbachol stimulation, a counterclockwise hysteresis is observed. This could be due to an increased sensitivity to Ca²⁺ mainly in tonic smooth muscle. These observations might be explained by a modulation of the Ca²⁺ sensitivity by sensitizing and desensitizing mechanisms. These modulations during different stimuli could be due to different myosin light-chain kinase/myosin light-chain phosphatase ratios.     

The human force:velocity relationship; activity in the knee flexor and extensor muscles before and after eccentric practice

The human voluntary force:velocity relationship frequently fails to demonstrate the expected high eccentric forces. Possible explanations include unique activation strategies which might be affected by neural learning mechanisms. We investigated the effect of practicing eccentric contractions on (1) the force: velocity relationship of the human knee extensor muscles and (2) the extent of agonist and antagonist muscle activity. Eight healthy adults [seven women, group mean age 31 (SEM 5) years ± ] practised twice a week for 4 weeks using their non-dominant legs. Each session comprised three isokinetic concentric and eccentric maximal voluntary contractions (MVC) at randomised angular velocities of 100, 200 and 300° · s⁻¹. Before and after, the force:velocity relationship was determined bilaterally (angular velocities 0–300° · s⁻¹). There were no significant differences in the forces generated or relative electromyogram (EMG) activity after practice, although there was a trend for dynamic forces to increase. Beforehand, the bilateral eccentric MVC forces were lower than isometric (P < 0.0025); afterwards they were broadly similar. The agonist EMG was similar during isometric and eccentric contractions, but lower during concentric (P < 0.03). Antagonist EMG activity showed considerable individual variation, was similar during all contraction types and tended to be greater during dynamic contractions. These data indicate that neither central learning mechanisms nor total muscle activation strategies underlie the human failure to produce the expected high eccentric voluntary forces in humans. Accepted: 19 September 2000     

A comparison of prehension force control in young and elderly individuals

Age-related changes were investigated in the control of precision grip force during the lifting and holding of objects with slippery (silk) and nonslippery (sandpaper) surface textures. Two groups of active elderly adults comprising individuals aged 69–79 years (n = 10), and 80–93 years (n = 10) together with a group of young adults aged 18–32 years (n = 10) participated in the study. Each subject lifted a free weight (3N) during which time gripping and lifting forces were monitored. The elderly subjects, especially the individuals in the 81–93 year group, had a larger number of fluctuations in the grip force rate curve and longer force application time than the younger subjects during lifting. The effect of prior experience with one surface on the following different surface was more pronounced in the younger subjects than the elderly subjects. These results suggest a decline in programmed force production capacity with increased age. The fingers of the elderly subjects were more slippery and they exhibited a greater safety margin of the grip force while holding the object than the younger adults. The overall results demonstrated that precision grip force control capacity declines with advancing age. It is suggested that this decline is due mainly to age-related changes in skin properties, and cutaneous sensibility functions, and in part to central nervous system function.     

Evidence against a role of nitric oxide in the indirect negative inotropic-effect of M-cholinoceptor stimulation in human ventricular myocardium

Nitric oxide (NO) has been reported to mediate several effects in response to muscarinic cholinergic stimulation in cardiovascular tissues. Recently, an attenuation of guinea pig cardiac myocyte contraction by NO has been described. The aim of the present study was to determine whether the indirect negative inotropic effect of M-cholinoceptor stimulation in human myocardium is in part due to an effect of endogenous NO. Therefore, the effect of carbachol was studied under control conditions and during inhibition of NO-synthase by pretreatment with N^G-monomethyl-l-arginine (NMMA). Functional experiments were performed in isolated, electrically driven (1 Hz, 37°C) left ventricular papillary muscle strips of human myocardium. Since cytokines have been reported to be increased in the serum of patients with heart failure and could induce NO-synthase activity in failing myocardium, we compared samples from nonfailing and terminally failing (classified as NYHA IV) hearts. The indirect negative inotropic effect of carbachol (10 mol/l) was studied in the presence of the \-adrenoceptor agonist isoprenaline (0.03 mol/l).After stimulation with isoprenaline, carbachol significantly (P < 0.05) reduced force of contraction. This effect was diminished in failing myocardium compared to nonfailing, probably due to the diminished inotropic response most likely due to the lower cAMP levels in response to \-adrenoceptor stimulation in the former condition. Pretreatment with NMMA (100 mol/l) altered the antiadrenergic effect of carbachol neither in nonfailing nor in failing preparations. Furthermore, inhibition of guanylyl cyclase, the target enzyme of NO, by preincubation with methylene blue (10 mol/l) for 30 min had no effect on the carbachol-induced decrease in force of contraction. Basal force of contraction, as well as the positive inotropic effect of isoprenaline remained unaffected by NMMA or methylene blue.The present study provides evidence that the indirect negative inotropic effect of M-cholinoceptor agonists is not due to an effect of NO in the human myocardium. Furthermore, the well known enhancement of cGMP in response to M-cholinoceptor stimulation appears not to be involved in this antiadrenergic effect.     

A force transducer and a length-ramp generator for mechanical investigations of frog-heart myocytes

An apparatus for studying the mechanics of isolated frog heart myocytes is described. The cells are held horizontal in a through of Ringer solution by means of two suction micropipettes. Myocyte force is measured with an opto-electronic system recording the deflection of the tip of one micropipette, which acts as a cantilever force probe. The force probes are selected for compliance according to the force a myocyte is expected to develop in a given condition, so as to limit myocyte shortening during force development to no more than 1% of the slack cellular length (l ₀). The other micropipette, which is stiff relative to the forces measured, is mounted on an electromagnetic-loudspeaker motor by which controlled-velocity length changes, of preset size and in either direction, are imposed on myocytes. The force transducer has a sensitivity of 5–10 mV/nN, with a frequency response of 700–900 Hz in Ringer solution and a resolution of 0.5–1 nN. The motor with a suction micropipette can complete controlled-velocity length ramps within 1.5–2.0 ms, across a range of ±100 m at a resolution of 8.0 nm. These values correspond, for frog-heart myocytes 200 m and 400 m long, to 25%–50% l ₀ and 0.002%–0.004% l ₀ respectively.     

电子表式止血带的设计

把电子计时器功能和传统卡式止血带相结合，设计出一种带有计时报警功能的电子表式止血带。具有一定的先进性和创新性，     

Oral Fine Motor Control of Teeth Treated with Endodontic Microsurgery: A Single-Blinded Case-control Study

IntroductionPeriodontal mechanoreceptors (PMRs) are refined neural receptors present in abundance at the root apex and have a pivotal role in oral fine motor control. This case-control study aimed to evaluate the oral fine motor control of teeth treated with endodontic microsurgery (EMS) in comparison with the control teeth using a standardized behavioral biting task.MethodsFourteen eligible participants performed 5 trials of an oral fine motor control task that involved holding and splitting half of a peanut positioned on a force transducer with their EMS treated tooth and its contralateral control incisor tooth (28 teeth in total). The outcome variables were the mean food holding force, intra- and intertrial variability of the holding force, food splitting force, splitting duration, and the frequency of the stepwise splitting phase. The data were analyzed with parametric and nonparametric tests.ResultsThe results showed no statistically significant differences in the holding force, inter- and intratrial variability of the holding force, splitting force, or splitting duration between the teeth treated with EMS and the control (P > .05). However, there was a significantly higher frequency of stepwise ramp increase during the splitting phase with EMS treated teeth compared with the control (48% and 37%, respectively; P < .05).ConclusionsEMS treated teeth showed similar force regulation and oral fine motor control as the contralateral control. The findings of this study suggest that EMS treatment does not perturb the sensory information of PMRs and maintains the force regulation and oral fine motor control of the teeth.     

Learning about Practice from Practice: A Peer-based Methodology

A recommendation from the Social Work Task Force was that all employers of social workers should conduct a regular “health check” of the social work profession to learn from practice as part of a continuous cycle of improvement. This article documents how the London Borough of Tower Hamlets has gone about this. I describe the methodological and practical pathway we followed so that others can see what we did and why we did it. Like other busy social work offices, we had to set out a plan of methodological action in order that we achieved the learning from practice to inform our health check, and it is the planning work that is engaged with in this article. We have found that by involving and engaging our staff in the health check work, we have gained more than we had set out to find. An organisational commitment to act on what social workers have told us about practice is offering the senior management team new ideas about the best ways of delivering professional and reflective support mechanisms for staff. Learning from practice is now one of the core functions for the new Principal Social Worker.