Effects of repeated waist-pull perturbations on gait stability in subjects with cerebellar ataxia

Background Damage to the cerebellum can affect neural structures involved in locomotion, causing gait and balance disorders. However, the integrity of cerebellum does not seem to be critical in managing sudden and unexpected environmental changes such as disturbances during walking. The cerebellum also plays a functional role in motor learning. Only a few effective therapies exist for individuals with cerebellar ataxia. With these in mind, we aimed at investigating: (1) corrective response of participants with cerebellar ataxia (CA) to unexpected gait perturbations; and (2) the effectiveness of a perturbation-based training to improve their dynamic stability during balance recovery responses and steady walking. Specifically, we hypothesized that: (1) CA group can show a corrective behavior similar to that of a healthy control group; (2) the exposure to a perturbation-based treatment can exploit residual learning capability, thus improving their dynamic stability during balance recovery responses and steady locomotion. Methods Ten participants with cerebellar ataxia and eight age-matched healthy adults were exposed to a single perturbation-based training session. The Active Tethered Pelvic Assist Device applied unexpected waist-pull perturbations while participants walked on a treadmill. Spatio-temporal parameters and dynamic stability were determined during corrective responses and steady locomotion, before and after the training. The ANalysis Of VAriance was the main statistical test used to assess the effects of group (healthy vs CA) and training (baseline vs post) on spatio-temporal parameters of the gait and margin of stability. Results Data analysis revealed that individuals with cerebellar ataxia behaved differently from healthy volunteers: (1) they retained a wider base of support during corrective responses and steady gait both before and after the training; (2) due to the training, patients improved their anterior-posterior margin of stability during steady walking only. Conclusions Our results revealed that participants with cerebellar ataxia could still rely on their learning capability to modify the gait towards a safer behavior. However, they could not take advantage from their residual learning capability while managing sudden and unexpected perturbations. Accordingly, the proposed training paradigm can be considered as a promising approach to improve balance control during steady walking in these individuals

Pre-Impact Detection Algorithm to Identify Tripping Events Using Wearable Sensors

This study aimed to investigate the performance of an updated version of our pre-impact detection algorithm parsing out the output of a set of Inertial Measurement Units (IMUs) placed on lower limbs and designed to recognize signs of lack of balance due to tripping. Eight young subjects were asked to manage tripping events while walking on a treadmill. An adaptive threshold-based algorithm, relying on a pool of adaptive oscillators, was tuned to identify abrupt kinematics modifications during tripping. Inputs of the algorithm were the elevation angles of lower limb segments, as estimated by IMUs located on thighs, shanks and feet. The results showed that the proposed algorithm can identify a lack of balance in about 0.37 ± 0.11 s after the onset of the perturbation, with a low percentage of false alarms (<10%), by using only data related to the perturbed shank. The proposed algorithm can hence be considered a multi-purpose tool to identify different perturbations (i.e., slippage and tripping). In this respect, it can be implemented for different wearable applications (e.g., smart garments or wearable robots) and adopted during daily life activities to enable on-demand injury prevention systems prior to fall impacts

Caratterizzazione di sistemi indossabili per il recupero della prensione in soggetti disabili

Lesioni del midollo spinale (SCI), malattie neurodegenerative e ictus cerebrale sono esempi di eventi invalidanti, poiché possono ridurre le capacità motorie delle persone colpite. La stimolazione elettrica funzionale (FES), introdotta in minima parte nella pratica clinica, induce elettricamente la contrazione muscolare per produrre movimenti funzionali utili. Per sfruttare la FES è necessario che il motoneurone inferiore prossimo alla placca motoria non sia danneggiato, in modo da poter indurre la contrazione muscolare desiderata. Un movimento funzionalmente utile per un individuo è la presa di un oggetto. Il movimento della mano comprende il coinvolgimento di molti muscoli atti all’apertura e alla chiusura delle dita, ed è complesso perché controlla svariati gradi di libertà attraverso complesse sinergie. Evolutivamente la mano umana si è differenziata da quella di altri animali, riducendo la sua specializzazione e aumentandone l’adattabilità. Forma, funzionalità e duttilità del controllo vanno di pari passo per adattarsi a interagire efficacemente con l’ambiente. Sono classificati diversi tipi di presa (presa sferica, cilindrica, gancio, laterale etc.) e ognuno di questi impatta in modo diverso con le ADL (activity of daily living). Per valutare la funzionalità dei diversi tipi di presa è possibile effettuare il test di Sollerman sulla funzionalità della mano [1]. Un paziente, a differenza di una persona in salute, potrebbe non essere in grado di compiere tutti i tipi di presa, potrebbe avere solo un controllo parziale della mano, potrebbe essere incapace di aprire la mano o avere tremori che gli impediscono la presa ferma di oggetti. Per questo motivo esistono sistemi di riabilitazione. E’ stato sviluppato un sistema assistivo per il controllo dei movimenti della mano tramite stimolazione transdermica, come modulo per il progetto MUNDUS (MUltimodal Neuroprosthesis for Daily Upper limb Support). Il sistema ha due componenti: un dispositivo per la stimolazione elettrica funzionale, e un guanto per monitorare i movimenti in atto. La stimolazione è applicata all’avambraccio e alla mano tramite matrici di elettrodi. Un guanto sensorizzato determina lo stato cinematico di apertura e di chiusura della mano e di forza applicata in punti caratteristici per la presa di un oggetto. Per semplicità di controllo è stato scelto di indurre la presa cilindrica di oggetti. In particolare, il guanto è in grado di rilevare i movimenti delle articolazioni metacarpali (MCP) e interfalangee prossimali (PIP) delle dita, e la presenza di una forza agente sulla punta delle dita e sul palmo della mano. Il sistema può essere controllato a ciclo aperto o a ciclo chiuso, rispettivamente per la fase d’identificazione e di controllo sulla forza. La fase d’identificazione è stata effettuata per decidere i parametri di stimolazione: posizione dell’elettrodo, frequenza di stimolazione, intensità di corrente e larghezza d’impulso (PW). Infatti, spostandosi da un elettrodo all’altro sull’array di elettrodi, e al contempo mantenendo fissi gli altri parametri di stimolazione, è possibile ottenere una risposta muscolare differente. La successiva fase di controllo è stata implementata in due modi diversi: attraverso un controllore bang-bang e attraverso un controllore PI (proporzionale-integrale). I due controllori forniscono allo stimolatore i parametri di controllo necessari per raggiungere lo stato desiderato (come ad esempio la presa di un oggetto). Il lavoro di tesi è stato suddiviso in 6 capitoli. Nel capitolo uno sono stati introdotti elementi di anatomia della mano, dei muscoli estrinseci ed intrinseci, della selettività della stimolazione elettrica nell’attivazione controllata dei muscoli e i limiti dell’approccio usato. Nel capitolo due sono stati descritti il guanto sensorizzato, il circuito di condizionamento del segnale e gli strumenti utilizzati per il test del guanto, per l’acquisizione, l’elaborazione e la visualizzazione dei dati grezzi o normalizzati. Nel capitolo tre è stato descritto l’array di elettrodi da posizionare sulla mano e sull’avambraccio per la stimolazione elettrica funzionale (FES) che induce l’apertura o la chiusura della mano. Nel capitolo quattro sono stati introdotti lo stimolatore e il demultiplexer necessari a indurre la stimolazione. Nel capitolo cinque sono state trattate le fasi di identificazione e controllo. Per quanto riguarda l’identificazione sono stati descritti gli strumenti usati per l’analisi, l’elaborazione e la visualizzazione offline dei dati acquisiti dal guanto, con l’obiettivo di identificare i parametri di stimolazione (corrente e sito di stimolazione). Per quanto riguarda il controllo, sono stati descritti i controllori utilizzati (bang-bang e PI) e i file generati per la loro l’implementazione. Nel capitolo sei sono stati riportati i risultati ottenuti dall’analisi del guanto, dalla fase di identificazione e dalla fase di controllo. Nel capitolo conclusivo è stato fatto un riassunto del lavoro di tesi, soffermandosi sulle limitazioni del sistema e sugli sviluppi futuri

Pre-Impact Detection Algorithm to Identify Tripping Events Using Wearable Sensors

This study aimed to investigate the performance of an updated version of our pre-impact detection algorithm parsing out the output of a set of Inertial Measurement Units (IMUs) placed on lower limbs and designed to recognize signs of lack of balance due to tripping. Eight young subjects were asked to manage tripping events while walking on a treadmill. An adaptive threshold-based algorithm, relying on a pool of adaptive oscillators, was tuned to identify abrupt kinematics modifications during tripping. Inputs of the algorithm were the elevation angles of lower limb segments, as estimated by IMUs located on thighs, shanks and feet. The results showed that the proposed algorithm can identify a lack of balance in about 0.37 +/- 0.11 s after the onset of the perturbation, with a low percentage of false alarms (<10%), by using only data related to the perturbed shank. The proposed algorithm can hence be considered a multi-purpose tool to identify different perturbations (i.e., slippage and tripping). In this respect, it can be implemented for different wearable applications (e.g., smart garments or wearable robots) and adopted during daily life activities to enable on-demand injury prevention systems prior to fall impacts

Intersegmental coordination elicited by unexpected multidirectional slippinglike perturbations resembles that adopted during steady locomotion

This study aimed at testing the hypothesis that reactive biomechanical responses elicited by unexpected slipping-like perturbations delivered during steady walking are characterized by an intersegmental coordination strategy resembling that adopted during unperturbed walking. Fifteen healthy subjects were asked to manage multidirectional slipping-like perturbations delivered while they walked steadily. The planar covariation law of elevation angles related to lower limb segments was the main observed variable related to unperturbed and perturbed strides. Principal component analysis was used to verify whether elevation angles covaried, both before and after the on set of the perturbation,and,if so,the orientation of the related planes of covariation was compared. Results revealed that the planar covariation law of the unperturbed limb after onset of the perturbation was systematically similar to that seen during steady walking. This occurred despite differences in range of motion and intersubject variability of both elevation and joint angles. The analysis strongly corroborates the hypothesis that the planar covariation law emerges from the interaction between spinal neural networks and limb mechanical oscillators. In particular, fast and stereotyped reactive strategies may result from the interaction among activities of downstream neural networks encrypting well-trained motor schemes, such as those related to walking, limb dynamics, and sensory motor information gathered during the perturbation. In addition, our results allowed us to speculate that rehabilitative treatment based on unexpected perturbations and relying on the plasticity of the central nervous system may also be effective in eliciting unimpaired intralimb coordination in neurological patients

Fast online decoding of motor tasks with single sEMG electrode in lower limb amputees

The quality of life of lower limb amputees strongly depends on the performance of their prosthesis. Active prostheses controlled by prosthesis sensors can participate to the movement and improve the walking performance of the amputees. However, a promising control mechanism involves the use of electromyography (EMG) to decode motor intentions. This approach could timely inform the prosthesis about the steps that the patient is going to perform much earlier compared to the feedback given by sensors. Here, we investigate whether an EMG-based algorithm is able to detect the motor intentions of transfemoral amputees. Subjects with a transfemoral amputation performed different motor tasks (e.g., ground level walking, climbing up/down stairs), while we recorded the EMG signals from surface electrodes placed on the subject’s stump. Our decoding algorithm achieved 100% motion intention discrimination. Such perfect decoding was achieved usually after less than 100 ms from the onset of the movement, thus ensuring that the information about the next step could be transmitted to the active prostheses with a sufficient advance to achieve its proper control. These results showed not only the feasibility of EMG-based online decoding of motor intentions, but also that perfect decoding can be achieved online with as little as one recording site, ensuring a minimum discomfort and encumbrance of the whole system

Effects of aging and perturbation intensities on temporal parameters during slipping-like perturbations

The aim of this study was to analyze the modifications of temporal parameters during slipping-like perturbations associated both with aging and perturbation intensities. Twelve participants equally distributed from two age groups (elderly and young) were recorded while, during steady locomotion, managing unexpected slipping-like perturbations, in forward direction, at different intensity and amplitude of foot shift. Two metrics were extrapolated from the analysis of the ground reaction force supplied by ad hoc platform aimed at destabilizing the balance control

Uncontrolled manifold analysis of the effects of a perturbation-based training on the organization of leg joint variance in cerebellar ataxia

Walking patterns of persons affected by cerebellar ataxia (CA) are characterized by wide stride-to-stride variability ascribable to: the background pathology-related sensory-motor noise; the motor redundancy, i.e., an excess of elemental degrees of freedom that overcomes the number of variables underlying a specific task performance. In this study, we first tested the hypothesis that healthy and, especially, CA subjects can effectively exploit solutions in the domain of segmental angles to stabilize the position of either the foot or the pelvis (task performance) across heel strikes, in accordance with the uncontrolled manifold (UCM) theory. Next, we verified whether a specific perturbation-based training allows CA subjects to further take advantage of this coordination mechanism to better cope with their inherent pathology-related variability. Results always rejected the hypothesis of pelvis stabilization whereas supported the idea that the foot position is stabilized across heel strikes by a synergic covariation of elevation and azimuth angles of lower limb segments in CA subjects only. In addition, it was observed that the perturbation-based training involves a decreasing trend in the variance component orthogonal to the UCM in both groups, reflecting an improved accuracy of the foot control. Concluding, CA subjects can effectively structure the wide amount of pathology-related sensory-motor noise to stabilize specific task performance, such as the foot position across heel strikes. Moreover, the promising effects of the proposed perturbation-based training paradigm are expected to improve the coordinative strategy underlying the stabilization of the foot position across strides, thus ameliorating balance control during treadmill locomotion