Ageing reduces light touch and vibrotactile sensitivity on the anterior lower leg and foot dorsum

Mechanoreceptor sensory feedback is impaired by pressure induced cutaneous ischemia on the human foot sole and can predict cutaneous microvascular reactivity

Introduction

The foot sole endures high magnitudes of pressure for sustained periods which results in transient but habitual cutaneous ischemia. Upon unloading, microvascular reactivity in cutaneous capillaries generates an influx of blood flow (PORH: post-occlusive reactive hyperemia). Whether pressure induced cutaneous ischemia from loading the foot sole impacts mechanoreceptor sensitivity remains unknown.

Methods

Pressure induced ischemia was attained using a custom-built-loading device that applied load to the whole right foot sole at 2 magnitudes (15 or 50% body weight), for 2 durations (2 or 10 minutes) in thirteen seated participants. Mechanoreceptor sensitivity was assessed using Semmes-Weinstein monofilaments over the third metatarsal (3MT), medial arch (MA), and heel. Perceptual thresholds (PT) were determined for each site prior to loading and then applied repeatedly to a metronome to establish the time course to return to PT upon unload, defined as PT recovery time. Microvascular flux was recorded from an in-line laser speckle contrast imager (FLPI-2, Moor Instruments Inc.) to establish PORH peak and recovery rates at each site.

Results

PT recovery and PORH recovery rate were most influenced at the heel and by load duration rather than load magnitude. PT recovery time at the heel was significantly longer with 10 minutes of loading, regardless of magnitude. Heel PORH recovery rate was significantly slower with 10minutes of loading. The 3MT PT recovery time was only longer after 10 minutes of loading at 50% body weight. Microvascular reactivity or sensitivity was not influenced with loading at the MA. A simple linear regression found that PORH recovery rate could predict PT recovery time at the heel (R2=0.184, p<0.001).

Conclusion

In populations with degraded sensory feedback, such as diabetic neuropathy, the risk for ulcer development is heightened. Our work demonstrated that prolonged loading in healthy individuals can impair skin sensitivity, which highlights the risks of prolonged loading and is likely exacerbated in diabetes. Understanding the direct association between sensory function and microvascular reactivity in age and diabetes related nerve damage, could help detect early progressions of neuropathy and mitigate ulcer development.

Heating the skin on the foot sole enhances cutaneous reflexes in the lower limb

Cutaneous input is important in postural control and balance. Aging and diabetes impair skin sensitivity and motor control. Heat application can improve skin sensation, but its influence on motor control remains unknown. This study investigated the effects of heating the skin of the foot sole on lower limb cutaneous reflexes. Reflexes were evoked in the tibialis anterior muscle of 20 young, healthy adults before and after heating the foot sole to a maximum of 42°C. While holding a 15% maximum root mean square EMG generated during maximum isometric dorsiflexion, a filtered white noise (0-50 Hz) vibration at 10 times the perceptual threshold was applied to the heel to stimulate cutaneous mechanoreceptors. Reflexes were analyzed in both the time (cumulant density) and frequency (coherence, gain) domains. Heat increased foot skin temperature ∼15.4°C (P < 0.001). Cumulant density peak to peak amplitude significantly increased by 44% after heating (P = 0.01) while latencies did not vary (P = 0.46). Coherence and gain were significantly greater in the 30- to 40-Hz range following heating (P = 0.048; P = 0.02). Heating significantly enhances lower limb cutaneous reflexes. This may be due to the increased ability of cutaneous mechanoreceptors to encode in the 30- to 40-Hz range.NEW & NOTEWORTHY Cutaneous input is a known modulator of muscle activity. Targeting skin to intentionally enhance motor output has received little attention. We explored local skin heating to enhance skin sensitivity and found a significant increase in the amplitude, coherence, and gain of cutaneous reflexes in the tibialis anterior. Our current findings provide the first support for the use of heat as a viable and easily integrated modality in rehabilitation technology to improve balance and postural control.

Short-term foot warming impacts foot sensitivity and body sway differently in older adults

BACKGROUND

Aging is accompanied by loss of foot skin sensitivity and reduced postural control. Increasing foot temperature can improve both skin sensitivity and postural control in adults. However, it remains unclear whether similar effects can be observed in older adults.

RESEARCH QUESTION

Can foot warming improve postural control in older adults, similar to observations in younger adults?

METHODS

Two foot warming protocols were conducted in 18 older adults (14 women, 4 men) to increase foot temperature by using infrared radiation to (1) warm the plantar aspect and (2) the skin of the entire foot and ankle area. We assessed the foot skin sensitivity before and after warming, considering tactile stimulation and center of pressure (CoP) displacement during 30-s standing with eyes open and closed.

RESULTS AND SIGNIFICANCE

Both foot warming protocols led to similar increases in skin temperature (∼6 °C) compared to the basal condition, but only warming the entire foot and ankle area increased foot sensitivity for the different regions assessed. No main effects or interactions were found for CoP variables in response to the two warming protocols. The short-term effects identified after warming the entire foot and ankle region suggest that this might be a strategy to improve skin sensitivity in older adults as observed in younger adults, but this was not the case for CoP. Future research should clarify whether the magnitude and long-lasting effects of warming could be determinant of CoP results.

The dynamic behavior of skin in response to vibrating touch stimuli affects tactile perception

BACKGROUND

The tactile perceptions arising on the skin mediate representations of the body and perceptions of the external physical world. Thus, these tactile sensations greatly impact our lives. Although tactile perception is caused by skin deformation, few studies have investigated the contribution of skin physical properties to tactile perception because the skin deformation in response to mechanical stimuli is difficult to measure in real time. In this study, we investigated how the skin deforms in response to externally applied mechanical stimuli and the effect of skin deformation on tactile perception.

MATERIALS AND METHODS

Tactile perception was assessed using psychophysical methods. A suction device was used to measure skin deformation in response to mechanical stimuli while assessing tactile perception. The relationship between skin deformation and tactile perception was investigated.

RESULTS

Individuals show different skin deformation behavior in response to stimuli of the same intensity, and the amount of skin deformation affects the perceived pressure induced by suction stimulation. Furthermore, when the amount of skin deformation is small, tactile perception becomes more difficult, and the ease of tactile perception varies.

CONCLUSION

We argue that dynamic skin behavior is an important factor in tactile perception. Focusing on skin physical characteristics from a constructivist perspective of complex tactile perception may lead to improved tactile communication perception through the control of skin physical properties and realistic tactile presentation in remote environments.

Cutaneous Sensitivity Across Regions of the Foot Sole and Dorsum are Influenced by Foot Posture

Understanding the processing of tactile information is crucial for the development of biofeedback interventions that target cutaneous mechanoreceptors. Mechanics of the skin have been shown to influence cutaneous tactile sensitivity. It has been established that foot skin mechanics are altered due to foot posture, but whether these changes affect cutaneous sensitivity are unknown. The purpose of this study was to investigate the potential effect of posture-mediated skin deformation about the ankle joint on perceptual measures of foot skin sensitivity. Participants (N = 20) underwent perceptual skin sensitivity testing on either the foot sole (N = 10) or dorsum (N = 10) with the foot positioned in maximal dorsiflexion/toe extension, maximal plantarflexion/toe flexion, and a neutral foot posture. Perceptual tests included touch sensitivity, stretch sensitivity, and spatial acuity. Regional differences in touch sensitivity were found across the foot sole (p < 0.001) and dorsum (p < 0.001). Touch sensitivity also significantly increased in postures where the skin was compressed (p = 0.001). Regional differences in spatial acuity were found on the foot sole (p = 0.002) but not dorsum (p = 0.666). Spatial acuity was not significantly altered by posture across the foot sole and dorsum, other than an increase in sensitivity at the medial arch in the dorsiflexion posture (p = 0.006). Posture*site interactions were found for stretch sensitivity on the foot sole and dorsum in both the transverse and longitudinal directions (p < 0.005). Stretch sensitivity increased in postures where the skin was pre-stretched on both the foot sole and dorsum. Changes in sensitivity across locations and postures were believed to occur due to concurrent changes in skin mechanics, such as skin hardness and thickness, which follows our previous findings. Future cutaneous biofeedback interventions should be applied with an awareness of these changes in skin sensitivity, to maximize their effectiveness for foot sole and dorsum input.

Remote Subthreshold Stimulation Enhances Skin Sensitivity in the Lower Extremity

Foot sole skin interfaces with the ground and contributes to successful balance. In situations with reduced sensitivity in the glabrous foot skin, stochastic resonance (SR) improves skin sensitivity by adding tactile noise. Some situations, however, involve an interface comprised of hairy skin, which has higher thresholds for sensitivity. For example, in lower extremity amputation the residual limb is comprised of hairy leg skin. The main objective of this study was to determine if SR improves skin sensitivity in hairy skin, and whether a specific intensity of noise is most effective. Secondary objectives were to compare the effect between locations, ages and modalities. In 60 healthy participants a vibrotactile (test) input was delivered at the lower extremity concurrently with a second, noisy stimulus applied more proximally. The presence of a remote SR effect was tested in 15 young participants using electrotactile noise at the calf. Secondary objectives were tested in separate groups of 15 subjects and differed by substituting for one of the three variables: vibrotactile noise, heel site, and with older participants. A forced-choice protocol was used to determine detection ability of the subthreshold vibration test input with varying noise levels applied simultaneously (0, 20, 40, 60, 80, and 100% of perceptual threshold). An SR effect was identified when increased detection of the input was obtained at any level of noise versus no noise. It was found that all four test groups demonstrated evidence of SR: 33–47% of individuals showed better detection of the input with added noise. The SR effect did not appear consistently at any specific noise level for any of the groups, and none of the variables showed a superior ability to evoke SR. Interestingly, in approximately 33% of cases, threshold values fluctuated throughout testing. While this work has provided evidence that SR can enhance the perception of a vibrotactile input in hairy skin, these data suggest that the ability to repeatably show an SR effect relies on maintaining a consistent threshold.

Heating the Skin Over the Knee Improves Kinesthesia During Knee Extension

To determine how heating affects dynamic joint position sense at the knee, participants (n = 11; F = 6) were seated in a HUMAC NORM dynamometer. The leg was passively moved through extension and flexion, and participants indicated when the 90° reference position was perceived, both at baseline (28.74 ± 2.43 °C) and heated (38.05 ± 0.16 °C) skin temperatures. Day 2 of testing reduced knee skin feedback with lidocaine. Directional error (actual leg angle–target angle) and absolute error (AE) were calculated. Heating reduced extension AE (baseline AE = 5.46 ± 2.39°, heat AE = 4.10 ± 1.97°), but not flexion. Lidocaine did not significantly affect flexion AE or extension AE. Overall, increased anterior knee-skin temperature improves dynamic joint position sense during passive knee extension, where baseline matching is poorer. Limited application of lidocaine to the anterior thigh, reducing some skin input, did not influence dynamic joint position sense, suggesting cutaneous receptors may play only a secondary role to spindle information during kinesthetic tasks. Importantly, cutaneous input from adjacent thigh regions cannot be ruled out as a contributor.

Vibrotactile sensitivity testing for occupational and disease-induce peripheral neuropathies

The International Standard Organization (ISO) standard 13091-1 describes methods and procedures for performing the vibrotactile perception threshold (VPT) testing to diagnose changes in tactile sensory function associated with occupational exposures. However, the VPT test also has been used in the diagnosis of peripheral neuropathies associated with a number of disorders. This review examines the VPT test, variations in procedures that have been used, as well as disorders and diseases in which this test has been reliable for the detection of sensory changes. Mechanisms potentially underlying the changes in VPTs are also discussed along with procedural and subject/patient factors that may affect the interpretation of test results. Based upon the review of the literature, there are also suggestions for where additional research might improve the administration of this test, depending upon the subject/patient population and interpretation of data.

Aging and the Relationship between Balance Performance, Vestibular Function and Somatosensory Thresholds

OBJECTIVES

The objective of this study was two-fold: (1) To evaluate the impact of the physiological aging process on somatosensory, vestibular, and balance functions, and (2) To examine the extent to which age and somatosensory and vestibular functions can predict balance performance.

MATERIALS AND METHODS

In this cross-sectional study, 141 asymptomatic subjects were assessed for touch pressure thresholds (TPT) with Semmes-Weinstein monofilaments (SWF), vibration thresholds (VT) with a neurothesiometer (NT) and a Rydel-Seiffer tuning fork 128Hz (RSTF). Horizontal vestibulo-ocular reflexes (HVOR gain and asymmetry) were assessed using the video Head Impulse Test (vHIT). A modified version of the Romberg test was used to assess standing balance and the Timed Up and Go test (TUG) and tandem gait (TG) to evaluate dynamic balance.

RESULTS

Significant age effects were found for TPT, VT, and balance but not for HVOR gain or asymmetry. Standing balance was explained for 47.2% by age, metatarsal 1 (MT1) (NT), and heel (SWF). The variance in TUG performance was explained for 47.0% by age, metatarsal 5 (MT5) (SWF), and medial malleolus (MM) (NT). Finally, the variance in TG performance was predicted for 43.1% by age, MT1 (NT), HVOR gain, and heel (SWF).

CONCLUSION

Among asymptomatic adult population, both somatosensation and balance performance deteriorate with aging. In contrast, HVOR remains rather constant with age, which is possibly explained by the process of vestibular adaptation. Furthermore, this study provides evidence that the VT, TPT, HVOR gain, and age partly predict balance performance. Still, further research is needed, especially with bigger samples in decades 8 and 9.

Comfortably numb? Experiences of people with stroke and lower limb sensation deficits: impact and solutions

PURPOSE

To explore personal experiences of loss of foot sensation following stroke in order to inform the focus of clinical assessments and development of a vibrotactile insole.

METHODS

Qualitative design with an interpretive phenomenological approach to data collection and analysis. Eight community dwelling adults with stroke (>6 months) and sensory impairment in the feet participated. Data was collected via conversational style interviews which were transcribed and analyzed using a thematic framework. Themes were verified with co-researchers and a lay advisory group.

RESULTS

Data formed four themes: Sensory deficits are prevalent and constant, but individual and variable; Sensory deficits have a direct impact on balance, gait, mobility and falls; Sensory deficits have consequences for peoples' lives; Footwear is the link between function, the environment and identity. They embraced the concept of discrete vibrotactile insoles, their potential benefits and demonstrated a willingness to try it.

CONCLUSIONS

Sensory deficit contributes to effects upon physical function, mobility and activity. Clinical outcome measures need to capture the emotional, psychological and social impacts of sensory deficit. Participants demonstrated a resilience and resourcefulness through adaption in daily living and self-management of footwear. The participants focus on footwear provides the opportunity to develop discrete and non-burdensome vibrotactile insoles for this patient group.IMPLICATIONS FOR REHABILITATIONSensory deficits are wide ranging and varied and are not distinct from motor deficits though contribute to the overall effect on physical function, mobility and activity.The physical effects impact on participants' lives emotionally, psychologically and socially. Measurement of outcomes need to capture specific activities that are valued by patients.The participants have revealed resilience and resourcefulness to create a "new normal" for their lives through adaption and self-management with a focus being on footwear as a solution.The participants have revealed the need for insole interventions to be discreet and non-burdensome, welcoming insole technology and contributing to the design and features of such insoles.