Mechanical Noise Improves the Vibration Perception Threshold of the Foot in People With Diabetic Neuropathy

Velocity ratings and perceptual qualities of electrotactile stimulation of the foot sole are impacted by direction, stimulus interval, and cutaneous saltation

Electrotactile stimulation is a çmethod of activating the tactile system by bypassing cutaneous mechanoreceptors and exciting the cutaneous afferent endings directly. This method is of interest for its potential in wearable tactile augmentation technologies. The generation of meaningful electrotactile sensation could benefit cases of peripheral neuropathy or prosthesis. There are limitations in our understanding of an electrotactile stimulations' capacity to represent tactile sensibilities, and its susceptibility to missense. The spatiotemporal parameters of an electrotactile sequence were varied. The present work extends the assessment of subjective evaluations of localization, velocity, and descriptive qualities. We applied electrotactile pulses at three sites on the foot sole, using three patterns across these sites: toward the heel or toes. We tested at three interstimulus intervals (100 ms, 160 ms, 220 ms). Faster sequences produced higher velocity ratings. Sequence direction across the foot sole impacted velocity ratings-with heel-to-toe sequences demonstrating a higher velocity rating than toe-to-heel sequences. During faster sequences with site repetition, cutaneous saltation is likely causing missense during localization. The spatiotemporal missense did not impact velocity ratings. This indicates that certain aspects of electrotactile sequence perception, such as velocity, are preserved through tactile illusions. These findings may be used to increase the resolution of stimulating grids.

Effects of Foot Somatosensory Training on Plantar Somatosensory Function

Background Declines in foot somatosensory function can negatively impact balance and daily activities, particularly in older adults and individuals with neurological conditions. Despite this, effective physical therapeutic interventions to improve foot sensory function are limited. This study assessed the effects of targeted foot somatosensory training on plantar sensory function in healthy young adults. Methods Thirty-three healthy young adults (mean age 21.2 ± 0.7 years) were randomly assigned to one of three groups: (1) Discrimination group, (2) Attention group, or (3) Control group. The Discrimination group performed spatial attention tasks to identify weight positions on an instability board; the Attention group focused on timing tasks; and the Control group watched a video. Tactile pressure sensitivity and two-point discrimination of the plantar surface were measured before and after the intervention. Statistical analyses included Wilcoxon signed-rank tests and two-way repeated measures of analysis of variance (ANOVA). Results No significant differences were found in tactile pressure sensitivity. However, two-point discrimination thresholds for the big toe and the ball of the little toe were significantly reduced in the Discrimination group, indicating enhanced sensitivity. Conclusion Foot sensory training, particularly through discrimination tasks, may effectively improve plantar sensory function, suggesting potential clinical applications in individuals with sensory impairments.

Novel Vibrating Foot Orthoses for Improving Tactile Sensation in Type 2 Diabetes With Peripheral Neuropathy

Improving tactile sensation by vibrating insoles was recommended to prevent foot ulcers in diabetic peripheral neuropathy (DPN). Lack of an insole design for diabetics was a challenge. Clinical trials on applying vibrating insoles with noise and stochastic resonance (SR) stimulating tactile were also required. In this study, vibrating foot orthoses (VFO) with a total contact design based on orthotics were proposed to provide proper insoles for diabetes. This study aimed to determine if VFO were beneficial at enhancing tactile in DPN. VFO were developed in combination with individual's custom-made foot orthoses and stimulation signals-integrating random 0-100 Hz square wave pulse signals with pseudorandom white noise by a SR approach. Sixty patients with mild-to-severe DPN were randomized to conduct crossover experiments: using and without VFO for 60 minutes stimulation at 90% of individuals' vibration perception threshold (VPT) level. VPT values when using VFO at the 1st and 5th metatarsophalangeal joints of the left foot decreased by 9.35% ( [Formula: see text].001); 9.04% ( [Formula: see text].001), and of the right foot decreased by 7.63% ( [Formula: see text].001); 7.24% ( [Formula: see text].001), respectively. Without VFO, there was no significant difference. Subgroups of mild and moderate DPN tended to benefit greatly from utilizing VFO. VFO can improve tactile in DPN. VFO may contribute to restoring/prolonging tactile and protective sensations, also decreasing peripheral nervous system deterioration. VFO might be useful for neurorehabilitation, and help prevent foot ulcers and disabilities.

Novel Tactile Stimulation Using A Vibratory Foot Orthosis: A Preliminary Study

Tactile loss caused by diabetic peripheral neuropathy (DPN) might result in foot ulceration and lower extremity amputation. Neurorehabilitation with a vibrating insole is one of the novel therapies for improving tactile sensibility. In this preliminary study, a vibratory foot orthosis (VFO) in conjunction with a random square wave pulse stimulus and pseudorandom white noise (PRWN) via a stochastic resonance (SR) method was newly designed for tactile stimulation. Effectiveness of using the VFO to stimulate tactile sensation was investigated in ten DPN patients. The pretest and posttest outcomes were determined by the vibration perception threshold (VPT) values at the 1st metatarsophalangeal joint (MTP) and 5th MTP. The results demonstrated that novel tactile stimulation by the VFO could reduce the VPT values by 11.33%, P<.001, 1st MTP (left foot); 10.44%, P=.002, 5th MTP (left foot); 8.96%, P=.001, 1st MTP (right foot); and 8.92%, P=.003, 5th MTP (right foot). In conclusion, a new design for tactile stimulation using the VFO can improve tactile sensation in DPN. The prototype of this developed VFO can offer excellent vibratory stimulation while being non-invasive and safe to use. An orthotic design for diabetic foot and a total contact design of the VFO can alleviate the challenges of a previous vibrating insole. The VFO might contribute to avoid foot ulcers, recurrent foot ulcers, and lower limb impairments. Significantly, the VFO may aid in the prevention of lower limb disabilities and be beneficial for neurorehabilitation.

Retention of Improved Plantar Sensation in Patients with Type II Diabetes Mellitus and Sensory Peripheral Neuropathy after One Month of Vibrating Insole Therapy: A Pilot Study

Sensory peripheral neuropathy is a common complication of diabetes mellitus and the biggest risk factor for diabetic foot ulcers. There is currently no available treatment that can reverse sensory loss in the diabetic population. The application of mechanical noise has been shown to improve vibration perception threshold or plantar sensation (through stochastic resonance) in the short term, but the therapeutic use, and longer-term effects have not been explored. In this study, vibrating insoles were therapeutically used by 22 participants, for 30 min per day, on a daily basis, for a month by persons with diabetic sensory peripheral neuropathy. The therapeutic application of vibrating insoles in this cohort significantly improved VPT by an average of 8.5 V (p = 0.001) post-intervention and 8.2 V (p < 0.001) post-washout. This statistically and clinically relevant improvement can play a role in protection against diabetic foot ulcers and the delay of subsequent lower-extremity amputation.

Subthreshold white noise vibration alters trembling sway in older adults

BACKGROUND

Somatosensory deficit is a significant contributor to falls in older adults. Stochastic resonance has shown promise in recent studies of somatosensation-based balance disorders, improving many measures of stability both inside and outside of the clinic. However, our understanding of this effect from a physiological perspective is poorly understood. Therefore, the primary goal of this study is to explore the influence of subthreshold vibratory stimulation on sway under the rambling-trembling framework.

METHODS

10 Healthy older adults (60-65 years) volunteered to participate in this study. Each participant underwent two randomized testing sessions on separate days, one experimental and one placebo. During each session, the participants' baseline sway was captured during one 90-s quiet standing trial. Their sensation threshold was then captured using a custom vibratory mat and 4-2-1 vibration perception threshold test. Finally, participants completed another 90-s quiet standing trial while the vibratory mat vibrated at 90% of their measured threshold (if experimental) or with the mat off (if placebo). While they completed these trials, an AMTI force plate collected force and moment data in the anteroposterior (AP) and mediolateral (ML), from which the center of pressure (COP), rambling (RM), and trembling (TR) time series were calculated. From each of these time series, range, variability (root-mean-square), and predictability (sample entropy) were extracted. One-tailed paired t-tests were used to compare baseline and during-vibration measures.

RESULTS

No significant differences were found during the placebo session. For the experimental session, significant increases were found in AP TR range, ML TR RMS, AP COP predictability, and AP & ML TR predictability. The TR time series was particularly sensitive to vibration, suggesting a strong influence on peripheral/spinal mechanisms of postural control.

SIGNIFICANCE

Though it is unclear whether observed effects are indicative of "improvements" or not, it does suggest that there was a measurable effect of subthreshold vibration on sway. This knowledge should be utilized in future studies of stochastic resonance, potentially acting as a mode of customization, tailoring vibration location, duration, magnitude, and frequency content to achieve the desired effect. One day, this work may aid in our ability to treat somatosensation-based balance deficits, ultimately reducing the incidence and severity of falls in older adults.

The Effect of Subliminal Electrical Noise Stimulation on Plantar Vibration Sensitivity in Persons with Diabetes Mellitus

Subliminal electrical noise (SEN) enhances sensitivity in healthy individuals of various ages. Diabetes and its neurodegenerative profile, such as marked decreases in foot sensitivity, highlights the potential benefits of SEN in such populations. Accordingly, this study aimed to investigate the effect of SEN on vibration sensitivity in diabetes. Vibration perception thresholds (VPT) and corresponding VPT variations (coefficient of variation, CoV) of two experimental groups with diabetes mellitus were determined using a customized vibration exciter (30 and 200 Hz). Plantar measurements were taken at the metatarsal area with and without SEN stimulation. Wilcoxon signed-rank and t tests were used to test for differences in VPT and CoV within frequencies, between the conditions with and without SEN. We found no statistically significant effects of SEN on VPT and CoV (p > 0.05). CoV showed descriptively lower mean variations of 4 and 7% for VPT in experiment 1. SEN did not demonstrate improvements in VPT in diabetic individuals. Interestingly, taking into account the most severely affected (neuropathy severity) individuals, SEN seems to positively influence vibratory perception. However, the descriptively reduced variations in experiment 1 indicate that participants felt more consistently. It is possible that the effect of SEN on thick, myelinated Aβ-fibers is only marginally present.

Early detection to prevent foot ulceration among type 2 diabetes mellitus patient: A multi-intervention review

Foot ulceration is one of the biggest complications experienced by type 2 diabetes patients. The severity and prevention of new wounds can be overcome through early detection interventions. This systematic review aims to explain and provide a comparison of various interventions that have been developed to prevent the occurrence of Diabetes Foot Ulcers (DFU). We searched Scopus, Science Direct, PubMed, CINAHL, SAGE, and ProQuest for English, experimental studies, published between 2016-2021 that tested early detection for preventing diabetic foot ulcers in diabetic patients. The Joanna Briggs Institute guidelines were used to assess eligibility, and PRISMA quality and a checklist to guide this review. 25 studies were obtained that matched the specified inclusion criteria. The entire article has an experimental study design. Majority of respondents were type 2 diabetes patients who have not experienced ulceration. Based on the results of the review, there were 3 main types of interventions used in the early detection of DFU. The types of intervention used are 1) conventional intervention/physical assessment, 2) 3D thermal camera assessment system, and 3) DFU screening instrument. The three types of interventions have advantages and disadvantages, so their use needs to be adjusted to the conditions and needs of the patient. the development of DFU risk early detection intervention needs to be developed. Integration with modern technology can also be done to increase the accuracy of the results and the ease of examination procedures.

Subthreshold Vibration Influences Standing Balance but Has Unclear Impact on Somatosensation in Persons With Transtibial Amputations

Stochastic resonance has been successfully used to improve human movement when using subthreshold vibration. Recent work has shown promise in improving mobility in individuals with unilateral lower limb amputations. Furthering this work, we present an investigation of two different signal structures in the use of stochastic resonance to improve mobility in individuals with unilateral lower limb amputations. Cutaneous somatosensation and standing balance measures using spatial and temporal analysis were assessed. There were no differences in the somatosensation measures, but differences in the temporal characteristics of the standing measures were seen with the various vibration structures when compared to no vibration, one of which suggesting mass may play an important role in determining who may or may not benefit from this intervention. Stochastic resonance employed with subthreshold vibration influences mobility in individuals with unilateral amputations, but the full direction and extent of influence is yet to be understood.

Immediate effects of footwear with vibration applied to the swing phase of the gait cycle on dynamic balance in patients with diabetic peripheral neuropathy

Sensory and sub-sensory foot vibration have beneficial effects on the static and dynamic balance of patients with diabetic peripheral neuropathy (DPN). Previous foot vibration during walking was applied at sub-sensory threshold in both stance and swing phases of the gait cycle in DPN. This study aimed to investigate the effects of footwear with vibration above the sensory threshold applied to the swing phase of the gait cycle on the dynamic balance of DPN. Fifteen patients with DPN and 10 matched healthy control participants were enrolled in this study. Dynamic balance assessment was investigated by the sit to stand and turn tests while electromyography activity (root mean square, RMS) of the vastus lateralis (VL), tibialis anterior (TA), and peroneus longus (PL) muscles were recorded at baseline, after 10 min of wearing the vibratory sandal without vibration, and after 10 min of wearing the sandal with vibration. Repeated measure analysis of variance was conducted for data analysis. Wearing the vibratory sandal slightly increased the speed of weight transfer in both groups and COP sway in DPN (P > 0.05), and close to significant decrease of turn sway (P = 0.07) in both groups. There were significant differences of the PL RMS in turn test (P = 0.03) in DPN and peak RMS of the PL after 10 min of wearing the sandal with vibration in both groups (P < 0.05). The results of the present study demonstrated that PL activity was significantly influenced by the vibratory sandal as its tendon passing across the sole and in direct contact with the source of the vibration.

The effects of mechanical noise bandwidth on balance across flat and compliant surfaces

Although the application of sub-sensory mechanical noise to the soles of the feet has been shown to enhance balance, there has been no study on how the bandwidth of the noise affects balance. Here, we report a single-blind randomized controlled study on the effects of a narrow and wide bandwidth mechanical noise on healthy young subjects’ sway during quiet standing on firm and compliant surfaces. For the firm surface, there was no improvement in balance for both bandwidths—this may be because the young subjects could already balance near-optimally or optimally on the surface by themselves. For the compliant surface, balance improved with the introduction of wide but not narrow bandwidth noise, and balance is improved for wide compared to narrow bandwidth noise. This could be explained using a simple model, which suggests that adding noise to a sub-threshold pressure stimulus results in markedly different frequency of nerve impulse transmitted to the brain for the narrow and wide bandwidth noise—the frequency is negligible for the former but significantly higher for the latter. Our results suggest that if a person’s standing balance is not optimal (for example, due to aging), it could be improved by applying a wide bandwidth noise to the feet.

Stochastic Resonance Reduces Sway and Gait Variability in Individuals With Unilateral Transtibial Amputation: A Pilot Study

Sub-threshold (imperceptible) vibration, applied to parts of the body, impacts how people move and perceive our world. Could this idea help someone who has lost part of their limb? Sub-threshold vibration was applied to the thigh of the affected limb of 20 people with unilateral transtibial amputation. Vibration conditions tested included two noise structures: pink and white. Center of pressure (COP) excursion (range and root-mean-square displacements) during quiet standing, and speed and spatial stride measures (mean and standard deviations of step length and width) during walking were assessed. Pink noise vibration decreased COP displacements in standing, and white noise vibration decreased sound limb step length standard deviation in walking. Sub-threshold vibration positively impacted aspects of both posture and gait; however, different noise structures had different effects. The current study represents foundational work in understanding the potential benefits of incorporating stochastic resonance as an intervention for individuals with amputation.

The Effect of Daily Use of Plantar Mechanical Stimulation Through Micro-Mobile Foot Compression Device Installed in Shoe Insoles on Vibration Perception, Gait, and Balance in People With Diabetic Peripheral Neuropathy

OBJECTIVE

People with diabetic peripheral neuropathy (DPN) have impaired gait and balance performance. The aim of this study is to investigate therapeutic effectiveness of mechanical stimulation through a wearable foot compression device equipped in a shoe insole on vibration perception, balance control and gait performance in people with DPN.

METHODS

Using a single-arm 4-week intervention study design, we examined effectiveness of daily use of shoes equipped with the foot compression device (Footbeat™, AVEX, Grand Junction, CO, USA) on improving vibration perception threshold (VPT_max), skin perfusion pressure (SPP), ankle brachial index (ABI), lower extremities edema (circumferences in the calf and ankle), and motor performance (postural sway with eyes open and closed conditions, and gait performance during normal, dual-task and fast walking). Thirty people with type 2 diabetes and symptoms of PN completed the experimental protocol.

RESULTS

Improvements in VPT_max (before = 27.4 V, after = 23.3 V, P = .007, d = 0.33, where d denotes effect size), center-of-mass sway in the mediolateral direction with both eyes open and closed conditions (before = 0.94 cm, after = 0.76 cm, P = .020, d = 0.47; before = 1.10 cm, after = 0.83 cm, P = .033, d = 0.66, respectively), and stride velocity for normal walking, dual-task walking and fast walking tasks (before = 0.87 m/s, after = 0.96 m/s, P = .017, d = 0.41; before = 0.75 m/s, after = 0.91 m/s, P = .001, d = 0.77; before = 1.10 m/s, after = 1.20 m/s, P = .043, d = 0.33, respectively) were found post treatment. There was no significant improvement in SPP, ABI, and circumferences in the calf and ankle.

CONCLUSIONS

Our findings suggest the wearable foot compression device may be effective for reducing neuropathic symptoms and enhancing motor performances in people with DPN.