Potential predictive effect of mechanical properties of the plantar skin and superficial soft tissue, and vibration perception on plantar loading during gait in individuals with diabetes.

BACKGROUND: This exploratory study aimed to investigate the extent to which mechanical properties of the plantar skin and superficial soft tissue (hardness, stiffness, and thickness) and vibration perception thresholds (VPTs) predict plantar pressure loading during gait in people with diabetes compared to healthy controls. METHODS: Mechanical properties, VPTs, and plantar loadings during gait at the heel and first metatarsal head (MTH) of 20 subjects with diabetes, 13 with DPN, and 33 healthy controls were acquired. Multiple regression analyses were used to predict plantar pressure peaks and pressure-time integrals at both locations based on the mechanical properties of the skin and superficial soft tissues and VPTs. RESULTS: In the diabetes group at the MTH, skin hardness associated with 30-Hz (R2 = 0.343) and 200-Hz (R2 = 0.314) VPTs predicted peak pressure at the forefoot. In the controls at the heel, peak pressure was predicted by the skin thickness, hardness, and stiffness associated with 30-Hz (R2 = 0.269, 0.268, and 0.267, respectively) and 200-Hz (R2 = 0.214, 0.247, and 0.265, respectively) VPTs. CONCLUSION: The forefoot loading of people with diabetes can be predicted by the hardness of the skin when combined with loss of vibration perception at low (30-Hz) and high (200-Hz) frequencies. Further data from larger sample sizes are needed to confirm the current findings.

Does plantar skin abrasion affect cutaneous mechanosensation?

In humans, plantar cutaneous mechanoreceptors provide critical input signals for postural control during walking and running. Because these receptors are located within the dermis, the mechanical properties of the overlying epidermis likely affect the transmission of external stimuli. Epidermal layers are highly adaptable and can form hard and thick protective calluses, but their effects on plantar sensitivity are currently disputed. Some research has shown no effect of epidermal properties on sensitivity to vibrations, whereas other research suggests that vibration and touch sensitivity diminishes with a thicker and harder epidermis. To address this conflict, we conducted an intervention study where 26 participants underwent a callus abrasion while an age-matched control group (n = 16) received no treatment. Skin hardness and thickness as well as vibration perception thresholds and touch sensitivity thresholds were collected before and after the intervention. The Callus abrasion significantly decreased skin properties. The intervention group exhibited no change in vibration sensitivity but had significantly better touch sensitivity. We argue that touch sensitivity was impeded by calluses because hard skin disperses the monofilament's standardized pressure used to stimulate the mechanoreceptors over a larger area, decreasing indentation depth and therefore stimulus intensity. However, vibration sensitivity was unaffected because the vibrating probe was adjusted to reach specific indentation depths, and thus stimulus intensity was not affected by skin properties. Since objects underfoot necessarily indent plantar skin during weight-bearing, calluses should not affect mechanosensation during standing, walking, or running.

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 Aß-fibers is only marginally present.

The Potential of Electrical Stimulation and Smart Textiles for Patients with Diabetes Mellitus.

Diabetes mellitus is one of the most frequent diseases in the general population. Electrical stimulation is a treatment modality based on the transmission of electrical pulses into the body that has been widely used for improving wound healing and for managing acute and chronic pain. Here, we discuss recent advancements in electroceuticals and haptic/smart devices for quality of life and present in which patients and how electrical stimulation may prove to be useful for the treatment of diabetes-related complications.

Low and High Frequency Vibration Perception Thresholds Can Improve the Diagnosis of Diabetic Neuropathy.

Recent studies demonstrate neuropathic changes with respect to vibration sensitivity for different measurement frequencies. This study investigates the relationship between vibration perception thresholds (VPTs) at low and high frequencies at two plantar locations and diabetic peripheral neuropathy (DPN) severity in diabetes mellitus (DM) subjects with DPN. We examine differences of VPTs between participants with DM, with DPN, as well as healthy controls. The influence of anthropometric, demographic parameters, and DM duration on VPTs is studied. Thirty-three healthy control group subjects (CG: 56.3 ± 9.9 years) and 33 with DM are studied. DM participants are subdivided into DM group (DM without DPN, n = 20, 53.3 ± 15.1 years), and DPN group (DM with DPN, n = 13, 61.0 ± 14.5 years). VPTs are measured at the first metatarsal head (MTH1) and heel (30 Hz, 200 Hz), using a customized vibration exciter. Spearman and Pearson correlations are used to identify relationships between VPTs and clinical parameters. ANOVAs are calculated to compare VPTs among groups. Significant correlations are observed between DPN severity (by fuzzy scores) and VPTs at both locations and frequencies (MTH1_30 Hz vs. fuzzy: r = 0.68, p = 0.011; Heel_30 Hz vs. fuzzy: r = 0.66, p = 0.014; MTH1_200 Hz vs. fuzzy: r = 0.73, p = 0.005; Heel_200 Hz vs. fuzzy: r = 0.60, p = 0.032). VPTs in CG and DM groups are significantly smaller than the DPN group, showing higher contrasts for the 30 Hz compared to the 200 Hz measurement. The correlations between fuzzy scores and VPTs confirm the relevance of using low and high frequencies to assess a comprehensive foot sensitivity status in people with DM.

Vibration Perception Thresholds of Skin Mechanoreceptors Are Influenced by Different Contact Forces.

Determining vibration perception thresholds (VPT) is a central concern of clinical research and science to assess the somatosensory capacity of humans. The response of different mechanoreceptors to an increasing contact force has rarely been studied. We hypothesize that increasing contact force leads to a decrease in VPTs of fast-adapting mechanoreceptors in the sole of the human foot. VPTs of 10 healthy subjects were measured at 30 Hz and 200 Hz at the heel of the right foot using a vibration exciter. Contact forces were adjusted precisely between 0.3 N-9.6 N through an integrated force sensor. Significant main effects were found for frequency and contact force. Furthermore, there was a significant interaction for frequency and contact force, meaning that the influence of an increasing contact force was more obvious for the 30 Hz condition. We presume that the principles of contrast enhancement and spatial summation are valid in Meissner and Pacinian corpuscles, respectively. In addition to spatial summation, we presume an effect on Pacinian corpuscles due to their presence in the periosteum or interosseous membrane.

The Mechanoreceptor's Role in Plantar Skin Changes in Individuals with Diabetes Mellitus.

Mechanical skin properties (MSPs) and vibration perception thresholds (VPTs) show no relationship in healthy subjects. Similar results were expected when comparing MSP and VPT in individuals with diabetes mellitus (DM) and with diabetic (peripheral-)neuropathy (DPN). A healthy control group (33 CG), 20 DM and 13 DPN participated in this cross-sectional study. DM and DPN were classified by using a fuzzy decision support system. VPTs (in µm) were measured with a modified vibration exciter at two different frequencies (30 and 200 Hz) and locations (heel, first metatarsal head). Skin hardness (durometer readings) and thickness (ultrasound) were measured at the same locations. DPN showed the highest VPTs compared to DM and CG at both frequencies and locations. Skin was harder in DPN compared to CG (heel). No differences were observed in skin thickness. VPTs at 30 and 200 Hz correlated negatively with skin hardness for DPN and with skin thickness for DM, respectively. This means, the harder or thicker the skin, the better the perception of 30 or 200 Hz vibrations. Changes in MSP may compensate the loss of sensitivity up to a certain progression of the disease. However, the influence seems rather small when considering other parameters, such as age.

Foot callus thickness does not trade off protection for tactile sensitivity during walking.

Until relatively recently, humans, similar to other animals, were habitually barefoot. Therefore, the soles of our feet were the only direct contact between the body and the ground when walking. There is indirect evidence that footwear such as sandals and moccasins were first invented within the past 40 thousand years1, the oldest recovered footwear dates to eight thousand years ago2 and inexpensive shoes with cushioned heels were not developed until the Industrial Revolution3. Because calluses-thickened and hardened areas of the epidermal layer of the skin-are the evolutionary solution to protecting the foot, we wondered whether they differ from shoes in maintaining tactile sensitivity during walking, especially at initial foot contact, to improve safety on surfaces that can be slippery, abrasive or otherwise injurious or uncomfortable. Here we show that, as expected, people from Kenya and the United States who frequently walk barefoot have thicker and harder calluses than those who typically use footwear. However, in contrast to shoes, callus thickness does not trade-off protection, measured as hardness and stiffness, for the ability to perceive tactile stimuli at frequencies experienced during walking. Additionally, unlike cushioned footwear, callus thickness does not affect how hard the feet strike the ground during walking, as indicated by impact forces. Along with providing protection and comfort at the cost of tactile sensitivity, cushioned footwear also lowers rates of loading at impact but increases force impulses, with unknown effects on the skeleton that merit future study.

Subliminal electrical and mechanical stimulation does not improve foot sensitivity in healthy elderly subjects.

OBJECTIVE: Deterioration of cutaneous perception may be one reason for the increased rate of falling in the elderly. The stochastic resonance phenomenon may compensate this loss of information by improving the capability to detect and transfer weak signals. In the present study, we hypothesize that subliminal electrical and mechanical noise applied to the sole of the foot of healthy elderly subjects improves vibration perception thresholds (VPT). METHODS: VPTs of 99 healthy elderly subjects were measured at 30 Hz at the heel and first metatarsal head (MET I). Participants were randomly assigned to one of five groups: vibration (Vi-G), current (Cu-G), control (Co-G), placebo-vibration (Pl-Vi), and placebo-current (Pl-Cu). Vi-G and Cu-G were stimulated using 90% (subliminal) of their individual perception thresholds for five minutes in a standing position. Co-G received no stimulation. The placebo groups were treated with mock stimulation. VPTs were measured twice before the intervention (baseline (BASE) and pre-measurement (PRE)), and once after the intervention (post-measurement (POST)). RESULTS: Significant differences were found between measurement conditions comparing BASE and POST, and PRE and POST. VPTs between groups within each measurement condition showed no significant differences. Vi-G was the only group that showed significantly higher VPTs in POST compared to BASE and PRE, which contradicts previous studies. CONCLUSION: We analyzed increased VPTs after subliminal mechanical stimulation. The pressure load of standing for five minutes combined with subliminal stimulation may have shifted the initial level of mechanoreceptor sensitivity, which may lead to a deterioration of the VPT. The subliminal electrical stimulation had no effect on VPT. SIGNIFICANCE: Based on our results, we cannot confirm positive effects of subliminal electrical or mechanical stimulation on the sole of the foot.