Antonio Nardone

MEDIUM-LATENCY STRETCH REFLEXES OF FOOT AND LEG MUSCLES ANALYSED BY COOLING THE LOWER LIMB IN STANDING HUMANS

1 In standing subjects, an ankle‐dorsiflexing perturbation of the supporting surface evokes a short‐latency response (SLR) and a medium‐latency response (MLR) to stretch in both soleus (Sol) and flexor digitorum brevis (FDB) muscles. The SLR is the counterpart of the monosynaptic reflex, whilst the MLR might be either mediated by Ia fibres, the delay being due to a long‐loop central circuit, or by fibres of slower conduction velocity. Since small afferents are slowed more than large ones by low temperature, a greater latency increment for the MLR than the SLR induced by cooling of the limb would point to a peripheral origin of the MLR. 2 In nine subjects, one limb was cooled by circulating water in a tube wrapped around it for about 120 min. Perturbations were delivered to the same limb prior to and during cooling, and after rewarming. EMG was recorded by surface electrodes from the Sol and FDB muscles. 3 The mean increase in latency of MLRs was significantly greater than that of SLRs in both muscles. On average, the Sol SLR increased from 42.4 to 47.0 ms and the Sol MLR from 72.0 to 82.3 ms. The FDB SLR increased from 58.1 to 66.5 ms and the FDB MLR from 94.9 to 110.5 ms. The mean difference (MLR minus SLR) increased from 29.6 to 35.2 ms for Sol, and from 36.8 to 43.9 ms for FDB at the end of cooling. After 30 min of rewarming, the responses of both muscles recovered towards control values. 4 The greater latency increment of the MLRs than of the SLRs favours the hypothesis of a slower conduction velocity of the responsible afferent fibres. The most likely candidate fibres are the spindle group II afferents.

Comparison of Reliability, Validity, and Responsiveness of the Mini-BESTest and Berg Balance Scale in Patients With Balance Disorders

Background Recently, a new tool for assessing dynamic balance impairments has been presented: the 14-item Mini-BESTest. Objective The aim of this study was to compare the psychometric performance of the Mini-BESTest and the Berg Balance Scale (BBS). Design A prospective, single-group, observational design was used in the study. Methods Ninety-three participants (mean age=66.2 years, SD=13.2; 53 women, 40 men) with balance deficits were recruited. Interrater (3 raters) and test-retest (1–3 days) reliability were calculated using intraclass correlation coefficients (ICCs). Responsiveness and minimal important change were assessed (after 10 sessions of physical therapy) using both distribution-based and anchor-based methods (external criterion: the 15-point Global Rating of Change [GRC] scale). Results At baseline, neither floor effects nor ceiling effects were found in either the Mini-BESTest or the BBS. After treatment, the maximum score was found in 12 participants (12.9%) with BBS and in 2 participants (2.1%) with Mini-BESTest. Test-retest reliability for total scores was significantly higher for the Mini-BESTest (ICC=.96) than for the BBS (ICC=.92), whereas interrater reliability was similar (ICC=.98 versus .97, respectively). The standard error of measurement (SEM) was 1.26 and the minimum detectable change at the 95% confidence level (MDC95) was 3.5 points for Mini-BESTest, whereas the SEM was 2.18 and the MDC95 was 6.2 points for the BBS. In receiver operating characteristic curves, the area under the curve was 0.92 for the Mini-BESTest and 0.91 for the BBS. The best minimal important change (MIC) was 4 points for the Mini-BESTest and 7 points for the BBS. After treatment, 38 participants evaluated with the Mini-BESTest and only 23 participants evaluated with the BBS (out of the 40 participants who had a GRC score of ≥3.5) showed a score change equal to or greater than the MIC values. Limitations The consecutive sampling method drawn from a single rehabilitation facility and the intrinsic weakness of the GRC for calculating MIC values were limitations of the study. Conclusions The 2 scales behave similarly, but the Mini-BESTest appears to have a lower ceiling effect, slightly higher reliability levels, and greater accuracy in classifying individual patients who show significant improvement in balance function.

Subjective perception of body sway

OBJECTIVES AND METHOD The relation between body sway recorded through a stabilometric platform and the subjective report of steadiness was studied in 20 young and 20 elderly subjects and 20 neuropathic and 20 parkinsonian patients standing upright. The trials were performed under two stances (feet apart, feet together) and two visual conditions (eyes open, eyes closed). At the end of each trial, subjects scored their performance on a scale from 10 (complete steadiness) to 0 (fall). RESULTS In all subjects, independently of the stance conditions, the larger the body sway the smaller the reported score. The function best fitting this relation was linear when sway was expressed on a logarithmic scale. The scoring reproducibility proved high both within and across subjects. Despite the different body sways and scores recorded under the different visual and postural conditions (eyes closed >eyes open, feet together>feet apart) in all groups of subjects and patients, the slopes of the relations between sway and score were broadly superimposable. In the normal subjects, the scores were slightly higher during eyes open than eyes closed trials for corresponding body sways. This was interpreted as a sign of perception of greater stability when vision was allowed. Parkinsonian patients swayed to a similar extent as normal subjects, and their scores were accordingly similar, both with eyes open and eyes closed. Neuropathic patients swayed to a larger extent than normal subjects, and their scores were matched appropriately. Although the slope of their relation with eyes closed was not different from that of normal subjects, with eyes open it was steeper and similar to that with eyes closed, suggesting that these patients did not feel more stable when they could take advantage of vision. CONCLUSIONS The subjective evaluation of body sway, irrespective of stance condition, age, neuropathy, and basal ganglia disease, reflects the actual sway, and is inversely proportional to the logarithm of the sway value. The remarkable similarity of the relation between score and sway across the various groups of subjects with eyes closed indicates a common mode of sway evaluation, possibly based on integration of several sensory inputs. All groups except neuropathic patients seem to take advantage of the redundancy of the inputs. Basal ganglia integrity does not seem to have a role in the evaluation of sway.

Group II spindle afferent fibers in humans: Their possible role in the reflex control of stance

Publisher Summary Since the first description by Ruffini of primary and secondary spindle endings, it has been tacitly assumed that they perform different reflex functions. While the role played in the monosynaptic response by group Ia afferents originating from the primary endings is generally agreed upon, some textbooks attribute to the small diameter myelinated group II afferent fibers, originating from the secondary endings, a role in producing flexor reflex effects. Accordingly, these fibers are classified as flexor reflex afferents together with high-threshold skin and joint afferents. Back in his preface to the 1972 Monograph of the Physiological Society, however, Matthews presented the notion that spindle group II fibers from secondary endings played a part in reflexly producing the hypertonia of the decerebrate preparation instead of merely contributing to a generalized flexor reflex. Group II afferent fibers that innervate muscle spindles discharge in response to muscle stretch and Ia fibers and are subjected to similar gamma and descending effects. Group II fibers can make both monosynaptic and oligosynaptic connections with homonymous and synergist hind-limb alpha motoneurons. A large number of spindle group II afferent fibers exist in the cat, and these fibers are roughly the same in number as the Ia fibers in all muscles in which they have been counted. It is highly possible that the same is true in humans, judging from the distribution of fibers of different diameter in the dorsal roots of the human lumbar spinal cord.

Stabilometry is a predictor of gait performance in chronic hemiparetic stroke patients

In patients with spastic hemiparesis, centre of foot pressure (CoP) is shifted toward the unaffected limb during quiet stance. We hypothesised that abnormal gait features would correlate with the degree of asymmetry during stance. In 15 patients and 17 normals we recorded CoP and body sway by a force platform and measured spatial-temporal variables of gait with pedobarography. In patients CoP was shifted toward the unaffected limb and sway was larger than in normals. CoP position was associated with the decrease in strength of the affected lower-limb muscles. Spatio-temporal variables of gait were also affected by the disease. Cadence and velocity were decreased, duration of single support on the unaffected limb and of double support were increased with respect to normals. The degree of impairment of gait variables correlated with CoP. We found a negative relationship between velocity or cadence and CoP, and a positive relationship between duration of single support and CoP in the unaffected but not in the affected limb. Duration of double support correlated positively with CoP. CoP asymmetry during both standing and walking suggests that postural and gait problems share some common neural origin in hemiparetic patients. This asymmetry affects gait performance by increasing the time and effort needed to shift body weight toward the affected limb. The degree of postural asymmetry measured by stabilometry is associated with the level of impairment of gait variables.

Stance control is not affected by paresis and reflex hyperexcitability: the case of spastic patients

OBJECTIVES Spastic patients were studied to understand whether stance unsteadiness is associated with changes in the control of voluntary force, muscle tone, or reflex excitability, rather than to abnormal posture connected to the motor deficit itself. METHODS Twenty four normal subjects, 12 patients affected by amyotrophic lateral sclerosis (ALS), seven by spastic paraparesis, and 14 by hemiparesis were studied. All patients featured various degrees of spasticity and paresis but were free from clinically evident sensory deficits. Body sway during quiet upright stance was assessed through a stabilometric platform under both eyes open (EO) and eyes closed (EC) conditions. The sudden rotation of a supporting platform, in a toe up and toe down direction respectively, evoked short (SLR) and medium latency (MLR) reflex responses to stretch of the soleus or the tibialis anterior (TA) muscle. RESULTS No relation was found between clinical findings (tone, muscle strength, tendon reflexes, plantar response, and duration of disease) and body sway. On average, all patient groups exhibited a forward shift of the centre of foot pressure (CFP) with respect to normal subjects; in addition, paraparetic and to a much larger extent hemiparetic patients showed a lateral shift of CFP. Body sway area was significantly increased only in the hemiparetic patients. No relation was found between position of the CFP and sway within any patient group. Soleus SLR was increased in all patients with respect to normal subjects. TA SLR was often seen in both patients with ALS and paraparetic patients, but only rarely in normal subjects and hemiparetic patients. However, no relation was found between amplitude of soleus or TA SLRs and stabilometric variables. The frequency and size of soleus MLR and TA MLR were decreased in all patients. These responses were decreased in size and not modulated by background EMG in the affected leg of hemiparetic patients, suggesting a disturbed control of spinal reflexes fed by spindle group II afferent fibres. CONCLUSIONS It is proposed that body posture, paresis, or monosynaptic reflex hyperexcitability do not affect the control of equilibrium during quiet upright stance. In hemiparetic patients, the decreased amplitude of MLRs might be the main cause of the large postural instability. The results are congruent with the hypothesis of a role for group II afferent input in the reflex control of equilibrium.

Influence of aging on leg muscle reflex responses to stance perturbation

The effect of age on latency and amplitude of leg muscle responses to stance perturbations was studied in 75 control subjects. They stood upright on a platform and were displaced by toe-up (upward tilt) and toe-down (downward tilt) platform rotations. Perturbations were induced during free and supported stance (holding on to a stable structure). Surface electromyograms (EMG) of the soleus (Sol) and tibialis anterior (TA) were recorded and latency and area of responses were measured. Body sway variables during stance with open or closed eyes were also recorded. Upward tilt evoked a short-latency response (SLR) in Sol and a long-latency response (LLR) in TA. Downward tilt evoked a medium-latency response (MLR) in TA and a LLR in Sol. This pattern of EMG responses was similar in both young and elderly subjects, although there were some differences in latency and amplitude. There was a significant relationship between latency of all responses and age. Slope of the regression lines of TA LLR, TA MLR, and Sol LLR was steeper than that of Sol SLR. Area of Sol SLR was unrelated to age, but a positive trend was identified in the other responses, significant for TA LLR. Under supported-stance condition, amplitude of TA MLR, TA LLR, and Sol LLR was decreased to a similar extent in both young and elderly subjects. There was a weak relationship between age and most body sway variables. A significant relationship was found between most sway variables and latency of Sol SLR and LLR, chiefly with eyes closed. Neither TA MLR nor LLR were significantly correlated with sway variables, but a trend was present for TA MLR with eyes closed.(ABSTRACT TRUNCATED AT 250 WORDS)

Eye tracking communication devices in amyotrophic lateral sclerosis: Impact on disability and quality of life

Abstract People with amyotrophic lateral sclerosis (PwALS) show progressive loss of voluntary muscle strength. In advanced disease, motor and phonatory impairments seriously hinder the patients interpersonal communication. High-tech devices such as eye tracking communication devices (ETCDs) are used to aid communication in the later stages of ALS. We sought to evaluate the effect of ETCDs on patient disability, quality of life (QoL), and user satisfaction, in a group of 35 regular ETCD users in late-stage ALS with tetraplegia and anarthria. The following scales were administered: 1) the Individually Prioritized Problem Assessment (IPPA) scale, in three conditions: without device, with ETCD and, when applicable, with an Eye Transfer (ETRAN) board; 2) the Psychosocial Impact of Assistive Devices Scale (PIADS); and 3) the Quebec User Evaluation of Satisfaction with Assistive Technology (QUEST 2.0). With ETRAN, IPPA showed an increase in communicative abilities with respect to the condition without device, but ETCD produced a further significant increase. PIADS evidenced a large increase of QoL, and QUEST 2.0 showed high user satisfaction with ETCD use. In conclusion, ETCDs should be considered in late-stage ALS with tetraplegia and anarthria, since in these patients they can reduce communication disability and improve QoL.

Balance Rehabilitation by Moving Platform and Exercises in Patients With Neuropathy or Vestibular Deficit

OBJECTIVE To assess the efficacy of a balance rehabilitation treatment by using both a powered platform on which subjects stand and specific physical exercises (EXs). DESIGN Crossover trial. SETTING Physical and rehabilitation medicine department in Italy. PARTICIPANTS Patients (N=33) with balance disorders (14 vestibular origin, 19 peripheral neuropathy origin). INTERVENTIONS Patients underwent powered platform then EX treatment (n=17); the other 16 received the same treatments in reverse order. powered platform consisted of balancing on a sinusoidally oscillating powered platform (in anteroposterior and laterolateral directions in separate trials) with eyes open and closed. A physical therapist administered Cawthorne-Cooksey EXs for patients with vestibular disorders and modified Frenkel EXs for patients with neuropathy. Treatment lasted 1 hour a day for 10 consecutive days, except for the weekend. MAIN OUTCOME MEASURES Body sway area, subjective score of stability, balance and gait scores, and amplitude of head displacement while balancing on the oscillating powered platform were recorded before, (t0) after the first (t1), and after the second treatment (t2), regardless of the powered platform or EX order. RESULTS On average, all participants improved balance regardless of the order of treatments, and more so at t2 than t1. Improvement was observed by using instrumental evaluations and balance and gait scales. In both patient groups, powered platform treatment proved to be as effective as EX in improving balance. This effect was stronger in patients with vestibular disorders, independently of order of treatment. CONCLUSIONS Balance rehabilitation with either EX or powered platform is effective in patients with balance disorders of vestibular or neuropathic origin. These findings point to the value of either or both physical EXs and powered platform in increasing stability and potentially decrease the risk of falling in patients with neuropathy, for whom few results are documented in the literature.

Alternate rhythmic vibratory stimulation of trunk muscles affects walking cadence and velocity in Parkinson’s disease

OBJECTIVE During the administration of timed bilateral alternate vibration to homonymous leg or trunk muscles during quiet upright stance, Parkinsonian (PD) patients undergo cyclic antero-posterior and medio-lateral transfers of the centre of foot pressure. This event might be potentially exploited for improving gait in these patients. Here, we tested this hypothesis by applying alternate muscle vibration during walking in PD. METHODS Fifteen patients and 15 healthy subjects walked on an instrumented walkway under four conditions: no vibration (no-Vib), and vibration of tibialis anterior (TA-Vib), soleus (Sol-Vib) and erector spinae (ES-Vib) muscles of both sides. Trains of vibration (internal frequency 100 Hz) were delivered to right and left side at alternating frequency of 10% above preferred step cadence. RESULTS During vibration, stride length, cadence and velocity increased in both patients and healthy subjects, significantly so for ES-Vib. Stance and swing time tended to decrease. Width of support base increased with Sol-Vib or TA-Vib, but was unaffected by ES-Vib. CONCLUSIONS Alternate ES vibration enhances gait velocity in PD. The stronger effect of ES over leg muscle vibration might depend on the relevance of the proprioceptive inflow from the trunk muscles and on the absence of adverse effects on the support base width. SIGNIFICANCE Trunk control is defective in PD. The effect of timed vibratory stimulation on gait suggests the potential use of trunk proprioceptive stimulation for tuning the central pattern generators for locomotion in PD.