The effects of peripheral nerve impairments on postural control and mobility among people with peripheral neuropathy

Approximately 20 million Americans are suffering Peripheral Neuropathy (PN). It is estimated that the prevalence of all-cause PN is about 2.4% in the entire adult population, whereas over 8-10% in the population segment over the age of 55 (Martyn & Hughes, 1997). Peripheral Neuropathy leads to a high risk of falling, resulting from the deficits of postural control caused by the impaired peripheral nerves, especially the degenerative somatosensory system. To date, there is no effective medical treatment for the disease but pain managements. The deficits of postural control decrease the life quality of this population. The degeneration of peripheral nerves reduces sensory inputs from the somatosensory system to central nervous system via spinal reflexive loop, which should provide valuable real-time information for balance correction. Therefore, it is necessary to investigate how PN affects the somatosensory system regarding postural control. Besides that, people with PN may develop a compensatory mechanism which could be reinforced by exercise training, ultimately to improve balance and mobility in their daily life. The neuroplasticity may occur within somatosensory system by relying on relative intact sensory resources. Hence, unveiling the compensatory mechanism in people with PN may help in understanding (a) essential sensations or function of peripheral nerves to postural control, (b) effective strategy of physical treatments for people with PN, and (c) task-dependent sensory information requirements. Therefore, this dissertation discussed the roles of foot sole sensation, ankle proprioception, and stretch reflex on balance as well as gait among people with PN. Furthermore, the discussion of the coupling between small and large afferent reflexive loops may spot the compensatory mechanism in people with PN

The Contribution of Small and Large Sensory Afferents to Postural Control in Patients With Peripheral Neuropathy

Peripheral neuropathy (PN) is a multifarious disorder that is caused by damage to the peripheral nerves. Although the symptoms of PN vary with the etiology, most cases are characterized by impaired tactile and proprioceptive sensation that progresses in a distal to proximal manner. Balance also tends to deteriorate as the disorder becomes more severe, and those afflicted are substantially more likely to fall while walking compared with those who are healthy. Most patients with PN walk more cautiously and with greater stride variability than age-matched controls, but the majority of their falls occur when they must react to a perturbation such as a slippery or uneven surface. The purpose of this study was to first describe the role of somatosensory feedback in the control of posture and then discuss how that relationship is typically affected by the most common types of PN. A comprehensive review of the scientific literature was conducted using MEDLINE, and the relevant information was synthesized. The evidence indicates that the proprioceptive feedback that is conveyed primarily through larger type I afferents is important for postural control. However, the evidence indicates that the tactile feedback communicated through smaller type II afferents is particularly critical to the maintenance of balance. Many forms of PN often lead to chronic tactile desensitization in the soles of the feet and, although the central nervous system seems to adapt to this smaller type II afferent dysfunction by relying on more larger type I afferent reflex loops, the result is still decreased stability. We propose a model that is intended both to help explain the relationship between stability and the smaller type II afferent and the larger type I afferent feedback that may be impaired by PN and to assist in the development of pertinent rehabilitative interventions

The Relationship of Plantar Sensation with Standing Balance and Gait Post-Stroke

Gait and balance dysfunction after stroke limit independence and quality of life. Numerous contributing factors have been investigated but the role of sensation deficits has received little attention. This thesis investigated the relationship between plantar cutaneous sensation and 1) standing balance, 2) gait, and 3) use of vision to compensate for sensory loss with a secondary analysis of data from individuals with subacute stroke. Associations between standing balance, gait and sensation were investigated with Spearman correlations. Individuals classified as impaired or intact sensation were compared on gait and standing balance measures. This thesis found plantar sensation is related to standing balance but not spatiotemporal gait parameters. Individuals with impaired sensation were not more likely to employ vision as a compensatory strategy. These results suggest plantar sensation should be addressed during post-stroke rehabilitation of standing balance. Future work should investigate changes in cutaneous sensation with recovery of balance and gait post-stroke

Cutaneous afferent innervation of the human foot sole: What can we learn from single unit recordings?

Cutaneous afferents convey exteroceptive information about the interaction of the body with the environment and proprioceptive information about body position and orientation. Four classes of low-threshold mechanoreceptor afferents innervate the foot sole and transmit feedback that facilitates the conscious and reflexive control of standing balance. Experimental manipulation of cutaneous feedback has been shown to alter the control of gait and standing balance. This has led to a growing interest in the design of intervention strategies that enhance cutaneous feedback and improve postural control. The advent of single-unit microneurography has allowed the firing and receptive field characteristics of foot sole cutaneous afferents to be investigated. In this review, we consolidate the available cutaneous afferent microneurographic recordings from the foot sole and provide an analysis of the firing threshold, and receptive field distribution and density of these cutaneous afferents. This work enhances the understanding of the foot sole as a sensory structure and provides a foundation for the continued development of sensory augmentation insoles and other tactile enhancement interventions

Textured insoles affect the plantar pressure distribution while elite rowers perform on an indoor rowing machine

Introduction: During rowing, foot positioning on the foot stretcher is critical to optimise muscle force transmission and boat propulsion. Following the beneficial effects of textured insoles on gait and balance, this study aims at investigating whether passive stimulation of foot mechanoreceptors induced by these insoles may contribute to improving foot loading pattern and symmetry during indoor rowing. Methods: Eleven elite rowers were assessed during controlled training on a standard rowing machine while wearing control, low-density or high-density textured insoles. Plantar pressure and knee and trunk kinematics were measured; performance data were recorded from the machine. Insole effect on kinematic parameters, peak and average values of foot force, contact area and position of centre of pressure was assessed with ANOVA and Bonferroni correction for pair-wise comparisons. Results: A main effect was observed for force and contact area, with the high-density insoles providing greatest values (P0.190), even though symmetry was higher with high-density insoles. Kinematics (P = 0.800) and rowing performance were not affected by insole type; a consistent though not statistically significant increase in mean travelled distance was observed for denser insoles (P>0.21). Conclusion: The high-density textured insoles affected foot loading distribution during indoor rowing. Rowers applied greater foot force and over a greater foot stretcher area with the high-density than the low-density and control insoles. These findings and the methodology applied may be relevant for the understanding and monitoring of rowing performance. © 2017 Vieira et al

The influence of peripheral neuropathy on walking kinematics and physical function

The 108th Congress (2005) has reported that 20 million U.S. citizens suffer from Peripheral Neuropathy (PN). Characterized by sensory nerve deterioration, PN reduces somatosensation (Padua et al., 2005) and increases the risk of fall-related injury (Richardson et al., 1992). The purpose of this dissertation was to provide insight into 1) the effects of acute loss of foot sole sensation on locomotor system health, 2) the effects of PN on locomotor system health, and 3) the underlying impairments associated with reduced physical function within the older adult and PN populations. Locomotor system health was assessed by the magnitude of stride-to-stride variability and local instability contained in the kinematics of treadmill walking. In healthy young adults, ice-induced reduction of foot sole sensation did not alter the magnitude of stride-to-stride variability during treadmill walking. It did, however, increase lower-extremity joint local instability, or the sensitivity to small scale perturbations. Compared to controls, individuals with PN walked with similar local instability yet increased variability, at relatively slow speeds. When walking at relatively fast speeds, individuals with PN exhibited exaggerated increases in local instability. In healthy older adults, locomotion-based physical function (LBPF), as defined by 6-minute walk and Timed Up-and-Go performance, was correlated to leg strength and measures of locomotor system health. However, only measures of locomotor system health provided independent predictive information of LBPF. The PN group exhibited reduced LBPF. As opposed to healthy old adults, correlates of LBPF were not leg strength but instead standing balance variables. Multiple variables of leg strength, standing balance, and locomotor system health provided independently predictive information regarding each test of LBPF. The opposing effects of ice-induced reduction in foot sole sensation and PN on locomotor system health suggest that the chronic nature of PN allows for the implementation of partially effective compensatory strategies. Yet, the inability to adapt to relatively fast speeds suggests that falls likely occur during challenging situations. The fundamentally different correlates and predictors of LBPF between older adults and those with PN highlight the uniqueness of the movement disorder associated with PN

Sensory and methodological aspects in biomechanical research of postural control and clinical fields of application

The human senses constitute a highly complex system based on various sensory organs, afferent pathways, and central processing locations, which allow us to interact with the environment, but also with ourselves. A further domain is important to achieve this interaction: the motor system, which allows linguistic communication and locomotion, for example. It becomes evident that sensory receptors work as a source of information to initiate, optimize, or cease motor activity. One generic term for such sensory sources is the somatosensory system, which is mainly based on receptors located in muscles, tendons, and the skin (cutaneous sensitivity). In this regard, it has been shown that cutaneous sensitivity contributes to human balance regulation. However, there are still debates concerning the exact role of plantar (foot sole) receptor inputs in particular, and how their isolated contribution to, e.g., balance regulation may be assessed accordingly. To investigate the interaction between plantar cutaneous sensitivity and human balance capabilities, several aspects need to be considered which are still controversial and inconclusive in the scientific community. For example, when assessing cutaneous vibration sensitivity, it is well-known that increasing vertical forces of the contactor toward the skin usually result in improved sensitivity. However, it has not been profoundly investigated whether assessing plantar vibratory sensitivity differs when comparing a standing or sitting posture, which obviously involves different contactor forces. In addition, many studies implementing cutaneous sensitivity show certain limitations with respect to adequate data analyses. A similar aspect also applies when assessing balance performance: devices allowing an investigation of dynamic balance performance (induced by unexpected platform perturbations while standing, for example) have only been partially investigated with regard to their biomechanical quality criteria, such as reliability. With these considerations in mind, the present doctoral thesis is based on five published studies. Study 1 investigates if plantar sensitivity is influenced by different body positions when collecting data. Study 2 asks how to appropriatly analze plantar sensitivity data. Study 3 examines the reliability of dynamic balance responses using the so-called Posturomed device, and Study 4 identifies the isolated role of plantar inputs on balance responses, when an acute sensory manipulation is induced that exclusively affects plantar aspects. Ultimately, clinical fields of application (based on the previous four studies) are highlighted in Study 5. The main findings of the first four studies can be summarized as follows. First, higher contact forces when standing compared to sitting did not influence plantar sensitivity. This is an important finding, as plantar sensitivity tests (often performed during sitting) may, hence, be brought into context with balance tests usually performed during standing. Second, plantar sensitivity data are shown to exhibit heteroscedasticity, meaning that the measurement error increases as the values increase. In Study 2, we provided an easy-to-follow example for how to account for heteroscedasticity by logarithmizing the raw data, and how to control whether this approach was successful in eliminating heteroscedasticity. Third, dynamic balance responses assessed via the Posturomed device exhibit an overall good reliability. Occasional significant differences were shown to be clinically non-relevant, identified by root mean square error calculations. Fourth, a permanent plantar sensory manipulation (hypothermia) was successfully achieved and maintained throughout data collection. Study 4 showed that the reduced plantar sensory input due to the hypothermic manipulation was compensated during more unchallenging balance conditions (standing still). There was no full compensation during more challenging balance conditions (unexpected platform perturbations during standing), however, with the body reacting with cautious motor behavior. This became evident by decreased outcome measures following hypothermic plantar sensory manipulation. These four studies shed further light onto investigations combining sensory and motor tests, especially with regard to physiological and methodological aspects that should be considered when analyzing and interpreting associated data. Finally, this doctoral thesis also provides an example of identifying clinical fields of application concerning sensory-focused research. In Study 5, we highlight the role of sensory research in the (early) diagnosis of diseases associated with cognitive decline. For this purpose, various instruments such as sensory tests or coordinative motor tests are implemented. Preliminary results suggest that not only classical cognitive parameters and questionnaires should be used to identify and better understand cognitive decline.Die menschlichen Sinne stellen ein sehr komplexes System dar, welches auf verschiedenen sensorischen Organen, afferenten Leitungsbahnen und zentralen Verarbeitungsstellen basiert und es uns ermöglicht, mit der Umwelt, aber auch mit uns selbst, zu interagieren. Dahingehend ist eine weitere wichtige Domäne wichtig, um diese Interaktion zu bewerkstelligen: das motorische System, welches etwa eine sprachliche Kommunikation oder auch die Fortbewegung ermöglicht. Es wird somit offensichtlich, dass sensorische Rezeptoren eine Informationsquelle darstellen, um motorische Aktivität zu initiieren, zu optimieren oder zu beenden. Ein grundlegender Terminus für solch sensorische Quellen ist das somatosensorische System, welches überwiegend auf Rezeptoren in Muskulatur, Sehnen und der Haut (kutane Sensibilität) beruht. Diesbezüglich wurde bereits aufgezeigt, dass die kutane Sensibilität einen Beitrag bei der menschlichen Gleichgewichtsregulation leistet. Allerdings existieren dabei nachwievor Diskussionen in Bezug auf die genaue Bedeutung plantarer (die Fußsohle betreffend) Rezeptor-Inputs und inwieweit deren isolierte Bedeutung bei der Gleichgewichtsregulation entsprechend ermittelt werden kann. Um die Interaktion zwischen der kutanen Sensorik der Fußsohle und der menschlichen Gleichgewichtsfähigkeit zu erforschen, sollten verschiedene Aspekte berücksichtigt werden, welche nachwievor kontrovers und nicht eindeutig in der Wissenschaft diskutiert werden. Bei Erhebungen der kutanen Vibrationssensibilität, als Beispiel, ist bereits bekannt, dass erhöhte Vertikalkräfte, mit denen der Vibrationsstößel gegen die Haut appliziert ist, generell zu einer verbesserten Sensibilität/Sensorik führen. Allerdings wurde noch nicht klar erforscht, ob sich die plantare Vibrationssensibilität zwischen einer stehenden und sitzenden Haltung der Probanden/innen unterscheidet, wobei hier natürlich unterschiedliche Vertikalkräfte der Stößel wahrscheinlich sind. Darüber hinaus zeigen viele Studien, welche die Hautsensibilität untersuchen, gewisse Limitierungen in Bezug auf eine adäquate Datenanalyse. Ein sehr ähnlicher Aspekt trifft auch auf die Evaluierung der Gleichgewichtsfähigkeit zu: Messgeräte, welche dabei eine Erfassung der dynamischen Gleichgewichtsfähigkeit zulassen (z.B. eingeleitet durch unerwartete Plattform-Perturbationen während des Stehens), wurden bisher nur teilweise auf die biomechanischen Gütekriterien hin untersucht, wie etwa die Reliabilität. Aufgrund dieser Überlegungen basiert die vorliegende Dissertation auf fünf publizierten Studien, welche folgende Aspekte untersuchten: Wird die plantare Sensibilität durch verschiedene Körperpositionen während der Datenaufnahme beeinflusst (Studie 1)? Wie können plantare Sensibilitätsdaten angemessen analysiert werden (Studie 2)? Darüber hinaus wurde ebenso untersucht, inwiefern das sogenannte 'Posturomed'-Messgerät bei der Beurteilung dynamischer Gleichgewichtsantworten reliable Messwerte liefert (Studie 3). Ferner wurde in Studie 4 untersucht, inwiefern isoliert plantare Inputsignale bei Gleichgewichtsantworten relevant sind (anhand einer akuten sensorischen Manipulation, welche ausschließlich die Fußsohle betrifft). In Studie 5 werden konkrete klinische Anwendungsbeispiele aufgrund der vier hier vorgestellten Studien aufgezeigt. Die Hauptergebnisse der ersten vier Studien können wie folgt zusammengefasst werden: Erstens, höhere vertikale Kontaktkräfte während des Stehens verglichen mit sitzenden Positionen führten zu keinen Unterschieden bzgl. der plantaren Sensibilität. Dies ist eine wichtige Erkenntnis, da plantare Sensorikmessungen (oft während des Sitzens durchgeführt) dadurch in Kontext mit Gleichgewichtstests gebracht werden können, welche normalerweise im Stehen erfolgen. Zweitens, Daten der plantaren Sensorik zeigten Heteroskedastizität, was bedeutet, dass sich der Messfehler mit Größenzunahme der Messwerte ebenso erhöht. Wir konnten in Studie 2 ein leicht zu erschließendes Beispiel aufzeigen, wie das Problem der Heteroskedastizität durch eine Logarithmierung der Rohdaten behandelt werden konnte und wie kontrolliert werden konnte, ob diese Behandlung erfolgreich war. Drittens, die dynamischen Gleichgewichtsantworten, welche mittels des 'Posturomed' ermittelt wurden, zeigen insgesamt eine gute Reliabilität. Gelegentlich auftretende signifikante Unterschiede wurden anhand von Berechnungen der Wurzel der mittleren Fehlerquadratsumme (root mean square error, RMSE) als klinisch nicht relevant eingestuft. Viertens, eine anhaltende plantar-sensorische Manipulation (Hypothermie) wurde erfolgreich eingeleitet und während der Datenerhebung aufrecht erhalten. Studie 4 zeigte ferner, dass die hypothermisch eingeleiteten reduzierten plantaren Sensorik-Inputs während der eher nicht herausfordernden quasi-statischen Gleichgewichtsbedingungen (einfaches aufrechtes Stehen) kompensiert werden konnten. Während der herausfordernden Gleichgewichtskonditionen (unerwartete Perturbationen der Plattform während des Stehens) hingegen wurde keine vollständige Kompensation erreicht. Allerdings reagierten die Probanden mit einem vorsichtigen motorischen Verhalten. Dies wurde durch die reduzierten Ergebnisparameter infolge der plantaren hypothermischen Manipulation ersichtlich. Die vier hier genannten Studien zeigen weitere Erkenntnisse in Bezug auf Forschungsaktivitäten, welche sensorische und motorische Tests vereinen. Dies trifft speziell in Hinblick auf physiologische und methodologische Aspekte zu, welche bei der Analyse und Interpretation derartiger Daten in Betracht gezogen werden sollten. Zuletzt bietet diese Arbeit auch ein Beispiel dafür, welche klinischen Anwendungsfelder im Bereich der sensorisch-fokussierten Forschung identifiziert werden können. In Studie 5 wird dafür die Bedeutung sensorischer Forschung bei der (Früh-) Diagnose von Erkrankungen aufgezeigt, welche mit kognitiven Einschränkungen in Verbindung gebracht werden. Für diesen Zweck werden verschiedene Instrumente eingebracht, wie etwa sensorische oder koordinativ-motorische Tests. Vorläufige Ergebnisse deuten dabei bereits an, dass nicht nur die klassischen kognitiven Parameter und Fragebögen bei der Identifizierung oder zum Zwecke des besseren Verstehens kognitiven Verfalls einbezogen werden sollten

Thresholds of cutaneous afferents related to perceptual threshold across the human foot sole

Perceptual thresholds are known to vary across the foot sole, despite a reported even distribution in cutaneous afferents. Skin mechanical properties have been proposed to account for these differences; however, a direct relationship between foot sole afferent firing, perceptual threshold, and skin mechanical properties has not been previously investigated. Using the technique of microneurography, we recorded the monofilament firing thresholds of cutaneous afferents and associated perceptual thresholds across the foot sole. In addition, receptive field hardness measurements were taken to investigate the influence of skin hardness on these threshold measures. Afferents were identified as fast adapting [FAI (n = 48) or FAII (n = 13)] or slowly adapting [SAI (n = 21) or SAII (n = 20)], and were grouped based on receptive field location (heel, arch, metatarsals, toes). Overall, perceptual thresholds were found to most closely align with firing thresholds of FA afferents. In contrast, SAI and SAII afferent firing thresholds were found to be significantly higher than perceptual thresholds and are not thought to mediate monofilament perceptual threshold across the foot sole. Perceptual thresholds and FAI afferent firing thresholds were significantly lower in the arch compared with other regions, and skin hardness was found to positively correlate with both FAI and FAII afferent firing and perceptual thresholds. These data support a perceptual influence of skin hardness, which is likely the result of elevated FA afferent firing threshold at harder foot sole sites. The close coupling between FA afferent firing and perceptual threshold across foot sole indicates that small changes in FA afferent firing can influence perceptual thresholds

Differential Effects of Reduced Foot Sole Sensitivity and Nerve Conduction Velocity on Postural Control and Functional Gait

INTRODUCTION: Peripheral neuropathy is characterized by a loss of foot sole sensitivity and slowed nerve conduction velocity. Individuals with peripheral neuropathy have decreased postural control ability and functional gait performance. No research was found that differentiated the effects of the main symptoms of peripheral neuropathy on postural control and functional gait. PURPOSE: The purpose of this study was to assess the differential effects of reduced foot sole sensitivity and slowed nerve conduction velocity on postural control and functional gait. METHODS: Two main clinical symptoms, H-index and foot sole sensitivity were evaluated among 35 participants. Outcome variables are the center of pressure standard deviation in the anteroposterior direction (SDAP) and the center of pressure average velocity (Vavg) during 30 seconds eyes open quiet standing, 6-minute walk distance (6MWD), and timed-up-and-go duration (TUG). RESULTS: Participants were separated into three groups symptomologically: Less affected (LA, 73±2 years old, 68.4±3.5kg, 1.62±0.02m, H-index: 89.7±3.4, range 78.0-109.4, cm2/ms2, Foot sole sensitivity score: 8.6±0.5, range 6-10), moderately affected (MA, 74±2 years old, 77.2±4.1kg, 1.65±0.02m, H-index: 60.2±3.4, range 42.8-76-6, cm2/ms2, Foot sole sensitivity score: 8.7±0.5, range 6-10), and severely affected (SA, 73±1 years old, 95.2±6.5kg, 1.73±0.03m, H-index: 61.8±2.1, range 45.6-75.5, cm2/ms2, Foot sole sensitivity score: 2.2±0.6, range 0-5). Multivariate analysis revealed significant group differences (