Effect of 4 Weeks of Foot Orthosis Intervention on Ambulatory Capacities and Posture in Normal-Weight and Obese Patients.

BACKGROUND: Several works have shown the benefits of foot orthosis intervention on postural stability in healthy individuals and patients with foot malalignment. However, the effects of foot orthoses on the daily ambulatory activities explored by the Six-Minute Walk Test (6MWT) were never examined. We hypothesized that foot orthoses could increase the gait distance and attenuate the post-6MWT posture alterations already reported in healthy individuals. METHODS: In ten normal-weight (NW) and ten obese patients with foot malalignment and/or abnormal foot arch, we examined the benefits of 4 weeks of custom-molded orthosis intervention (D30) on 6MWT gait distance, fatigue sensation scores, ankle plantarflexion force, and post-6MWT sway of the center of pressure (COP) measured by a pedobarographic platform. Data were compared with those measured in two control-matched groups of ten NW and ten obese individuals, explored at study inclusion and at D30. RESULTS: At study inclusion, the post-6MWT changes in COP surface and the medial and lateral COP deviations were significantly higher in obese participants who needed to wear the foot orthoses compared with obese control subjects. The foot orthosis intervention significantly improved the ambulatory performances of NW and obese individuals during the 6MWT, attenuated the bodily fatigue sensation after the 6MWT, and reduced the post-6MWT COP deviations, with the benefits of insoles being significantly accentuated in obese participants. CONCLUSIONS: Four weeks of foot orthosis intervention significantly increases gait distance and is an effective means to reduce postural sway after walking.

Normal Values of Pressures and Foot Areas Measured in the Static Condition.

BACKGROUND: Podiatric physicians are increasingly using pedobarographs to measure plantar pressure. However, normal values of static pedobarographic variables for healthy men and women are lacking, which makes it difficult to evaluate abnormal foot positioning in standing patients with low- or high-arched feet or painful feet. METHODS: During upright standing, a computerized pedobarograph measured the maximal (Pmax) and mean (Pmean) plantar pressures, total foot area, and forefoot and rearfoot areas in 84 healthy women and 84 healthy men, aged 18 to 83 years. After calibration of the pedobarograph, a correction factor was applied to area measurements, and data repeatability was assessed. RESULTS: The Pmax and Pmean values were not correlated with age but with weight, body mass index, and shoe size. Total foot area was significantly higher in male participants and correlated with body weight, body mass index, and shoe size but not with age. In both sexes, forefoot area was significantly lower than rearfoot area. Significant positive correlations were observed between forefoot and rearfoot areas and weight and shoe size. The forefoot-rearfoot area ratio did not vary with sex, weight, shoe size, and age. CONCLUSIONS: These data provide relationships between Pmax, Pmean, and foot areas and weight and shoe size and clearly indicate no age dependence of pedobarographic data. They also provide stable values of the forefoot-rearfoot area ratio. These data should help clinicians evaluate abnormal foot placement in standing patients.

Effect of the 6-minute walk test on plantar loading and capability to produce ankle plantar flexion forces.

The six-minute walk test (6MWT) is used to evaluate the ambulatory capacity of patients suffering from respiratory disorders, obesity or neuromuscular diseases. Our primary aim was to evaluate the effects of the 6MWT on the postural sway and the ankle plantar flexion forces in healthy subjects. We measured the ankle plantar flexion forces and the plantar contact area before and after a 6MWT in normal weight and overweight subjects with no history of respiratory, cardiac, and neuromuscular disorders. A post-6MWT sensation of bodily fatigue was evaluated by Multidimensional Fatigue Inventory (MFI) and Pichot fatigue scales. A computerized pedobarographic platform was used to collect the mean plantar contact area, the changes of the center of pressure (CoP) surface and its medial and lateral deviations. In a limited number of subjects, the reproducibility of all the measurements was explored. In both groups, the 6MWT elicited a sensation of bodily fatigue. It also significantly reduced the ankle plantar flexion forces, and increased both the mean plantar contact area and the CoP surface, the changes being not apparent after 10min. The post-6MWT lateral CoP deviations were accentuated in normal weight subjects, while an increase in medial CoP deviations occurred in overweight ones. The 6MWT-induced changes in the plantar flexion force and pedobarographic variables were reproducible. Because this study clearly showed some post-6MWT alterations of the subjects' posture sway of our subjects, we questioned the possible mechanisms occurring that could explain the altered muscle force and the transient destabilization of posture after the 6MWT.

Psychophysical estimate of plantar vibration sensitivity brings additional information to the detection threshold in young and elderly subjects.

OBJECTIVE: Vibration detection threshold of the foot sole was compared to the psychophysical estimate of vibration in a wide range of amplitudes in young (20-34 years old) and elderly subjects (53-67 years old). METHODS: The vibration detection threshold was determined on the hallux, 5th metatarsal head, and heel at frequencies of 25, 50 and 150 Hz. For vibrations of higher amplitude (reaching 360 µm), the Stevens power function (Ψ = k * Φn ) allowed to obtain regression equations between the vibration estimate (Ψ) and its physical magnitude (Φ), the n coefficient giving the subjective intensity in vibration perception. We searched for age-related changes in the vibration perception by the foot sole. RESULTS: In all participants, higher n values were measured at vibration frequencies of 150 Hz and, compared to the young adults the elderly had lower n values measured at this frequency. Only in the young participants, the vibration detection threshold was lowered at 150 Hz. CONCLUSION: The psychophysical estimate brings further information than the vibration detection threshold which is less affected by age. SIGNIFICANCE: The clinical interest of psychophysical vibration estimate was assessed in a patient with a unilateral alteration of foot sensitivity.

Pilot study demonstrating that sole mechanosensitivity can be affected by insole use.

Insoles are known to alter plantar loads and thus plantar sensory input. We therefore hypothesised that plantar somatosensory sensation could be modified over time by use of hard metatarsal pads. A sample of 12 healthy female participants was randomly allocated to either soft metatarsal pads (n=6, latex foam, Shore A11) or hard metatarsal pads groups (n = 6, thermoplastic, ShoreA65). All wore the same shoe type and pedometers measured daily activities. Using a bespoke actuated device, multiple mechanical stimuli were applied to the forefoot and rearfoot before and after 8 and 30 days of wearing the pads. A control test comprised estimation of multiple auditory sensations at day 0, 8 and 30. Changes in detection of the mechanical and sound stimuli were estimated using the Stevens power function, Ψ = k × Φ(n) (estimate = Ψ; stimulus = Φ). The k coefficient measured the sensitivity, i.e. the lowest detectable load/sound, and the n coefficient the gain in perception over time. After 30 days, hard metatarsal pads group had increased plantar sensitivity in the forefoot but not the rearfoot. The soft metatarsal pads group showed no changes in plantar sensitivity and the detection of auditory sensation remained stable over the 30 days.Metatarsal pads with relatively high hardness increased the perception of the lowest mechanical stimulus in the forefoot compared to soft metatarsal pads. This provides initial evidence of the potential for changes in plantar somatosensory sensation due to choice of orthotic designs in patients with foot-related problems.

Consequences of repetitive toenail cutting by podiatric physicians on force production, endurance to fatigue, and the electromyogram of the flexor digitorum superficialis muscles.

BACKGROUND: We hypothesized that the repetitive use of a toenail clipper by podiatric physicians could induce fatigue of the flexor digitorum superficialis (FDS) muscle, reducing the accuracy of toenail cutting. METHODS: We examined the consequences of cutting a plastic sheet, reproducing the resistance of thick toenails, with a podiatric medical clipper on the maximal handgrip force (Fmax) developed by the FDS muscle and an isometric handgrip sustained at 50% of Fmax, during which endurance to fatigue and changes in the power spectra of the surface FDS muscle electromyogram (root mean square and median frequency) were measured. The same participants randomly performed one or five runs of 30 successive cuttings, each on different days. RESULTS: After the first and fifth cutting runs, Fmax increased, suggesting a post-tetanic potentiation. During the handgrip sustained at 50% of Fmax, we measured a significant reduction in the tension-time index after the first cutting run. Moreover, after the fifth cutting run, the tension-time index decrease was significantly accentuated, and the decrease in FDS muscle median frequency was enhanced. No median frequency decline was measured during the cutting runs. CONCLUSIONS: These results suggest that the efficacy of occupational podiatric medical tasks progressively declines with the repetition of toenail cutting. We propose solutions to remedy this situation.

Changes in stationary upright standing and proprioceptive reflex control of foot muscles after fatiguing static foot inversion.

We searched for the consequences of a maximal static foot inversion sustained until exhaustion on the post-exercise stationary upright standing and the proprioceptive control of the foot muscles. Twelve healthy subjects executed an unilateral maximal static foot inversion during which continuous power spectrum analyses of surface electromyograms of the tibialis anterior (TA), peroneus longus (PL), and gastrocnemius medialis (GM) muscles were performed. Superimposed pulse trains (twitch interpolation) were delivered to the TA muscle to identify "central" or "peripheral" fatigue. Before and after the fatiguing task, we measured (1) the repartition of the plantar and barycentre surfaces with a computerized stationary platform, (2) the peak contractile TA response to electrical stimulation (TA twitch), (3) the tonic vibratory response (TVR) of TA and GM muscles, and (4) the Hoffman reflex. During static exercise, "central" fatigue was diagnosed in 5/12 subjects whereas in the 7 others "peripheral" TA fatigue was deduced from the absence of response to twitch interpolation and the post-exercise decrease in twitch amplitude. The sustained foot inversion was associated with reduced median frequency in TA but not in PL and GM muscles. After static exercise, in all subjects both the mean plantar and rearfoot surfaces increased, indicating a foot eversion, the TVR amplitude decreased in TA but did not vary in GM, and the Hoffman reflex remained unchanged. Whatever was the mechanism of fatigue during the maximal foot inversion task, the facilitating myotatic reflex was constantly altered in foot invertor muscles. This could explain the prevailing action of the antagonistic evertor muscles.

Decreased foot inversion force and increased plantar surface after maximal incremental running exercise.

Formulating the hypothesis that a maximal running exercise could induce fatigue of some foot muscles, we searched for electromyographic (EMG) signs of fatigue in the tibialis anterior (TA), peroneus longus (PL), and gastrocnemius medialis (GM) muscles. We also searched for post-exercise alterations of the stationary upright standing in normal-arched feet subjects. Healthy subjects performed a maximal running exercise. Surface EMGs of the TA, PL, and GM muscles were analysed during maximal dynamic efforts. Before and after the running bout, we measured the evoked compound muscle potential (M-wave) in TA, the maximal force into inversion (MIF), and the repartition of the plantar and barycentre surfaces with a computerised stationary platform. During maximal running exercise, the median frequency of the EMG spectra declined in TA while it remained stable in the PL and GM muscles. After the exercise, MIF decreased, and both the rearfoot plantar surface and the barycentre surface increased. We concluded that a maximal running bout elicits EMG signs of fatigue, though only in the TA muscle. It also elicits post-exercise changes in the foot position during stationary upright standing which indicates a foot eversion. These data solely concern a maximal running test and they can not be extrapolated to walking or running at a low speed.

3-(R)-[3-(2-methoxyphenylthio-2-(S)-methylpropyl]amino-3,4-dihydro-2H-1,5-benzoxathiepine bromhydrate (F 15845) prevents ischemia-induced heart remodeling by reduction of the intracellular Na+ overload.

The present study investigates whether 3-(R)-[3-(2-methoxyphenylthio-2-(S)-methylpropyl]amino-3,4-dihydro-2H-1,5-benzoxathiepine bromhydrate (F 15845), a new, persistent sodium current blocker, can reduce the ischemic Na(+) accumulation and exert short- and long-term cardioprotection after myocardial infarction. First, F 15845 concentration-dependently reduced veratrine-induced diastolic contracture (IC(50) = 0.14 microM) in isolated atria. Second, F 15845 from 1 microM preserved viability in 54.2 +/- 12.5% of isolated cardiomyocytes exposed to lysophosphatidylcholine. Third, the effect of F 15845 on intracellular Na(+) of isolated hearts from control and diabetic db/db mice was monitored using (23)Na-nuclear magnetic resonance spectroscopy. F 15845 (0.3 microM) significantly counteracted [Na(+)](i) increase during no-flow ischemia in control mouse hearts. In diabetic db/db mouse hearts, the reduction in [Na(+)](i) was delayed relative to control. However, it was more marked and maintained upon reperfusion. The cardioprotective properties after myocardial infarction associated with short- (24-h) and long-term (14-day) reperfusion were measured in anesthetized rats. After 24-h reperfusion, F 15845 (5 mg/kg) significantly reduced infarct size (32.4 +/- 1.7% with vehicle and 24.2 +/- 3.4% with F 15845; P < 0.05) and decrease of troponin I levels (524 +/- 93 microg/l with vehicle versus 271 +/- 63 microg/l with F 15845; P < 0.05). It is important that F 15845 limits the long-term expansion of infarct size (35.2 +/- 2.6%, n = 19 versus 46.7 +/- 1.6%, n = 27 in the vehicle group; P < 0.001). Overall, F 15845 attenuates [Na(+)](i) and prevents (or reverses) contractile and biochemical dysfunction in ischemic and remodeling heart. F 15845 constitutes a new generation of cardioprotective agent.

Effects of SM-20550 against myocardial infarction-induced arrhythmias, late infarct expansion, and left ventricular dysfunction.

The aim of the study was to evaluate the cardioprotective and antiarrhythmic effects of intravenous Na+/H+ blockers (cariporide and SM-20550) in a rat model of ischemia and a long period reperfusion (14 days). This model allowed study of the role of Na+/H+ exchanger against late myocardial infarct expansion and left ventricular dysfunction. Each compound was administered 5 min before ischemia. Cariporide (from 0.16 mg/kg) and SM-20550 (from 0.04 mg/kg) significantly and dose-dependently reduced the number of ventricular premature beats during ischemia. The duration of ventricular tachycardia was importantly shortened in the presence of cariporide (0.63 mg/kg) and SM-20550 (0.16 mg/kg). Furthermore, cariporide (0.63 mg/kg) and SM-20550 (from 0.04 mg/kg) significantly reduced the infarct expansion: 43 +/- 2% in the cariporide group and 42 +/- 2% at 0.16 mg/kg SM-20550 versus 48 +/- 1% in the vehicle group. Cariporide and SM-20550 significantly prevented the left ventricular free wall thinning associated with the thickness ratio, suggesting a significant reduction of the ventricular dilation. Cariporide and SM-20550 significantly improved the negative dP/dtmax, suggesting a partial restoration of the cardiac relaxation. Collectively, Na+/H+ blockers administered before ischemia reduced arrhythmias and also prevented the remodeling process of the heart during postinfarction.

A novel steroid-like compound F90927 exerting positive-inotropic effects in cardiac muscle.

Here we report a novel steroid-like compound F90363, exhibiting positive inotropy in vivo and in vitro in various cardiac muscle preparations. F90363 is a racemic mixture composed of the stereoisomers (-)-F90926 and (+)-F90927. Only F90927 exerted positive inotropy, while F90926 induced a weak negative inotropy, but only at concentrations 10(3) times higher than F90927 and most likely resulting from an unspecific interaction. The rapid time course of the action of F90927 suggested a direct interaction with a cellular target rather than a genomic alteration. We could identify the L-type Ca2+ current I(Ca(L)) as a main target of F90927, while excluding other components of cardiac Ca2+ signalling as potential contributors. In addition, several other signaling pathways known to lead to positive inotropy (e.g. alpha- and beta-adrenergic stimulation, cAMP pathways) could be excluded as targets of F90927. However, vessel contraction and stiffening of the cardiac muscle at high doses (>30 microM, 0.36 mg kg(-1), respectively) prevent the use of F90927 as a candidate for drug development. Since the compound may still find valuable applications in research, the aim of the present study was to identify the cellular target and the mechanism of inotropy of F90927.

Pharmacological characterisation of sodium channels in sinoatrial node pacemaking in the rat heart.

Blockade of sodium channels located in the sinoatrial node can slow diastolic depolarisation rate, recorded in vitro. The objective was therefore to determine whether these blockers could slow heart rate in vivo. The heart rate was firstly measured in spontaneously beating, isolated rat heart atria in the presence of different voltage gated sodium channel blockers. Tetrodotoxin and lidocaine slightly reduced heart rate whereas KC 12291 and R 56865, which mainly interact with the persistent component of the sodium current, concentration dependently and potently induced bradycardia. In the pithed rat, tetrodotoxin induced statistically significant decreases heart rate, maximal effects were: -32.2+/-6.1 beat per min. KC 12291 and R 56865 dose-dependently induced bradycardia (Delta heart rate obtained, -55.1+/-5.2 beat per min, P<0.05, and -71.9+/-8.5 bpm, P<0.05, respectively). In conclusion, voltage gated sodium channel blockers rather selective for the persistent current, exert a potent bradycardic effect in the rat.