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Biomedical subjects

Peter R Cavanagh

Publications and source records attributed to Peter R Cavanagh.

At least 19 recordsLinked to original sources
PubMed2006

Reaching upward is more challenging to dynamic balance than reaching forward.

BACKGROUND: Older adults have less confidence in their ability to reach upward compared to reaching forward. The forward reach test may, therefore, not be ideally suited for detecting functional deficits that directly affect daily activities. METHODS: A new test of upward reach and forward reach (along a 50-degree track) were administered to young and older adults. Reach distance was adjusted for foot length and normalized to stature. The anterior safety margin was calculated by relating the center of pressure to the base of support. The extent to which age, sex, balance confidence, anthropometric, and center of pressure parameters contribute to forward and upward reach performance was assessed. FINDINGS: Reach and anterior safety margin scores were well-correlated between forward and upward reaching, but the upward reach test posed a greater challenge to dynamic balance - eliciting a smaller anterior safety margin from both older and younger subjects. Further, compared to young adults, older adults showed greater limitations in reach distance and balance parameters during upward reach compared with forward reach. An observational measure of reach strategy (whether or not the heels were raised from the platform during the test) differentiated between higher and lower reach performance for older adults. Anthropometric variables accounted for much of the variance in reach performance that would otherwise have been attributed to an age-related loss of functional capacity. Balance confidence scores also contributed to regression models predicting upward - but not forward - reach performance in older adults. INTERPRETATION: Though upward and forward reach performances were well related in this sample, a test of upward reach may be better suited to reveal early signs of functional decline in older adults than a test of forward reach.

Adult↗
PubMed2006

Reliability of surface EMG measurements over 12 hours.

Bone and muscle are both compromised during long-term space flight. Experiments are, therefore, in progress using surface electromyography (EMG) and joint angle measurements to compare muscle action on earth and in space over complete working days. To date, there is little information on the reliability of such long-term EMG measurements available in the literature. Therefore, the current study determined the reliability and feasibility of using surface EMG over a 12-h interval. Ten young subjects performed standardized isometric exercises at 30% of maximum voluntary effort every 2h throughout a normal working day, which included a period of self-chosen exercise. Surface electrodes remained in place over the biceps brachii (BB), vastus medialis (VM), and gastrocnemius (GN) throughout the day. The normalized integrated EMG for two of the three muscles showed no significant changes during the 12-h period, and only the first observation for VM showed a trend (p<0.1) of differences with three of the other measurement periods. The stability of surface EMG measurements over the 12-h period suggests that this methodology is feasible for use in future long-term EMG studies.

Adult↗
PubMed2006

Comparison of knee motion on Earth and in space: an observational study.

BACKGROUND: Spaceflight has been shown to cause atrophy, reduced functional capacity, and increased fatigue in lower-limb skeletal muscles. The mechanisms of these losses are not fully understood but are thought to result, in part, from alteration in muscle usage. METHODS: Knee-joint angles and lower-extremity muscle activity were measured continually, via elecrogoniometry and surface electromyography respectively, from two subjects during entire working days of activity on Earth and onboard the International Space Station (ISS). RESULTS: On Earth the distribution of angular positions of the knee was typically bimodal, with peaks of >75 degrees of flexion and in almost full extension (<15 degrees of flexion). However, on the ISS, a single peak in the mid-range of the available range of motion was seen. The knee joint was also moved through fewer excursions and the excursions were smaller in amplitude, resulting in a reduced span of angles traversed. The velocities of the excursions in space were lower than those used on Earth. CONCLUSION: These results demonstrate that, in space, overall knee-joint motion is reduced, and there is a transformation in the type of muscle action compared to that seen on Earth, with more isometric action at the expense of concentric and particularly eccentric action.

Journal Article↗
PubMed2006

Nonsurgical strategies for healing and preventing recurrence of diabetic foot ulcers.

We have outlined an approach to the nonsurgical treatment of diabetic foot ulcers based on an understanding of their etiology. We have emphasized the importance of off-loading as the crucial element to success in healing foot ulcers and preventing their recurrence in those with diabetes. Computerized design of custom insoles can allow the unloading of elevated plantar pressure while incorporating the shape of the foot, which was formerly the major criterion used insole design.

Biomechanical Phenomena↗
PubMed2006

An inverse finite-element model of heel-pad indentation.

A numerical-experimental approach has been developed to characterize heel-pad deformation at the material level. Left and right heels of 20 diabetic subjects and 20 nondiabetic subjects matched for age, gender and body mass index were indented using force-controlled ultrasound. Initial tissue thickness and deformation were measured using M-mode ultrasound; indentation forces were recorded simultaneously. An inverse finite-element analysis of the indentation protocol using axisymmetric models adjusted to reflect individual heel thickness was used to extract nonlinear material properties describing the hyperelastic behavior of each heel. Student's t-tests revealed that heel pads of diabetic subjects were not significantly different in initial thickness nor were they stiffer than those from nondiabetic subjects. Another heel-pad model with anatomically realistic surface representations of the calcaneus and soft tissue was developed to estimate peak pressure prediction errors when average rather than individualized material properties were used. Root-mean-square errors of up to 7% were calculated, indicating the importance of subject-specific modeling of the nonlinear elastic behavior of the heel pad. Indentation systems combined with the presented numerical approach can provide this information for further analysis of patient-specific foot pathologies and therapeutic footwear designs.

Computer Simulation↗
PubMed2006

Patient Interpretation of Neuropathy (PIN) questionnaire: an instrument for assessment of cognitive and emotional factors associated with foot self-care.

OBJECTIVE: Using the common-sense model of illness behavior, we developed and validated a self-report instrument for assessment of patients' cognitive and emotional representations of diabetic peripheral neuropathy (DPN) influencing foot self-care. RESEARCH DESIGN AND METHODS: The Patient Interpretation of Neuropathy (PIN) questionnaire, generated from discussions with clinicians and interviews with patients with DPN, was administered to patients with DPN attending U.K. (n = 325) and U.S. (n = 170) diabetes centers. Psychometric tests of the PIN questionnaire comprised factor analysis, internal consistency, and test-retest reliability. Partial correlations and multivariate regressions established construct and criterion-related validity. The associations of PIN scales to past foot ulceration and foot self-care behaviors were compared with those using a generic measure of illness perception and emotion, the Revised Illness Perception Questionnaire (IPQ-R), which was adapted to neuropathy. RESULTS: Factor analysis of the PIN questionnaire produced 11 scales, which explained 69% of item variance. Nine factors measured patients' common-sense beliefs about DPN and their levels of understanding of DPN-related medical information. Two factors assessed the emotions of worry about potential consequences and anger at practitioners. Most scales demonstrated adequate internal (Cronbach's alpha = 0.62-0.90) and test-retest reliability (Pearson's r = 0.51-0.64). Partial correlations between the PIN and IPQ-R scales in corresponding domains were significant but modest (rp = 0.15-0.26). Finally, PIN scales showed significant associations with past foot ulceration and foot self-care behaviors, thereby confirming criterion validity. CONCLUSIONS: The 39-item PIN questionnaire is a reliable and valid measure of patients' cognitive and emotional representations of neuropathy affecting foot self-care.

Aged↗
PubMed2006

Gravity replacement during running in simulated microgravity.

INTRODUCTION: During treadmill exercise on the International Space Station (ISS), a restoring load from a subject load device (SLD) is applied through a shoulder-and-waist harness to pull the exercising crewmember toward the treadmill surface. The capacity of this arrangement to provide 1-g-like reaction forces may be critical for effective use of the treadmill as a countermeasure to musculoskeletal changes during prolonged spaceflight. This study in simulated microgravity evaluated the comfort and function during running of the ISS harness used with a new SLD in a system that allows more even distribution of the load between the waist and shoulders. METHODS: Using a zero-gravity locomotion simulator, 12 subjects completed three 5-min running trials at a constant speed (3.35 m x s(-1)) using three SLD loads [50%, 75%, and 100% of bodyweight (BW)] presented at random and a shoulder-to-waist loading ratio of 50:50. Subjective ratings of discomfort, ground reaction forces (GRFs), and SLD loads were collected. RESULTS: A load of 100% BW resulted in similar GRF profiles (peak and rate of change of force) to those reported for 1-g running over ground and were also comfortably tolerated (mean Borg scale rating 3.9/10). DISCUSSION: With an appropriate harness and SLD system, 1-g-like GRF profiles can be generated at the feet during simulated microgravity running. Such forces can be achieved with a level of discomfort rated better than "somewhat uncomfortable," suggesting that running with 1-g loads could be an effective component of musculoskeletal countermeasures during long-duration spaceflight.

Adult↗
PubMed2005

Treatment for diabetic foot ulcers.

People with diabetes develop foot ulcers because of neuropathy (sensory, motor, and autonomic deficits), ischaemia, or both. The initiating injury may be from acute mechanical or thermal trauma or from repetitively or continuously applied mechanical stress. Patients with clinically significant limb ischaemia should be assessed by a vascular surgeon to determine the need for angioplasty, stenting, or femorodistal bypass. When infection complicates a foot ulcer, the combination can be limb or life-threatening. Infection is defined clinically, but wound cultures reveal the causative pathogens. Tissue specimens are strongly preferred to wound swabs for wound cultures. Antimicrobial therapy should be guided by culture results, and should aim to cure the infection, not to heal the wound. Alleviation of the mechanical load on ulcers (off-loading) should always be a part of treatment. Neuropathic ulcers typically heal in 6 weeks with total contact casting, because it effectively relieves pressure at the ulcer site and enforces patient compliance. The success of other approaches to off-loading similarly depends on the patients' adherence to the effectiveness of pressure relief. Surgery to heal ulcers and prevent recurrence can include tenotomy, tendon lengthening, reconstruction, or removal of bony prominences. However, these procedures may result in secondary ulceration and other complications. Ulcer recurrence rates are high, but appropriate education for patients, the provision of posthealing footwear, and regular foot care can reduce rates of re-ulceration.

Amputation, Surgical↗
PubMed2005

Reduction of plantar heel pressures: Insole design using finite element analysis.

Plantar heel pain is a common condition that is often exacerbated by the repetitive stresses of walking. Treatment usually includes an in-shoe intervention designed to reduce plantar pressure under the heel by using insoles and a variety of off-the-shelf products. The design process for these products is often intuitive in nature and does not always rely on scientifically derived guidelines. Finite element analysis provides an efficient computational framework to investigate the performance of a large number of designs for optimal plantar pressure reduction. In this study, we used two-dimensional plane strain finite element modeling to investigate 27 insole designs. Combinations of three insole conformity levels (flat, half conforming, full conforming), three insole thickness values (6.3, 9.5 and 12.7 mm) and three insole materials (Poron Cushioning, Microcel Puff Lite and Microcel Puff) were simulated during the early support phase of gait. Plantar pressures predicted by the model were validated by experimental trials conducted in the same subject whose heel was modeled by loading the bare foot on a rigid surface and on foam mats. Conformity of the insole was the most important design variable, whereas peak pressures were relatively insensitive to insole material selection. The model predicted a 24% relief in pressure compared to barefoot conditions when using flat insoles; the reduction increased up to 44% for full conforming insoles.

Adult↗
PubMed2005

The role of proinflammatory cytokines in the cause of neuropathic osteoarthropathy (acute Charcot foot) in diabetes.

The pathogenesis of the acute Charcot foot of diabetes remains unclear. All patients with this condition have evidence of peripheral neuropathy, with loss of protective sensation and abnormal foot biomechanics. However, the acute Charcot foot is also characterised by a pronounced inflammatory reaction and the pathogenic significance of this inflammation has received little attention. We suggest that an initial insult--which may or may not be detected--is sufficient to trigger an inflammatory cascade through increased expression of proinflammatory cytokines, including TNFalpha and interleukin 1beta. This cascade then leads to increased expression of the nuclear transcription factor, NF-kappaB, which results in increased osteoclastogenesis. Osteoclasts cause progressive bone lysis, leading to further fracture, which in turn potentiates the inflammatory process. The potential role of proinflammatory cytokines suggests the possibility of new treatments for this sometimes devastating complication of diabetes.

Arthropathy, Neurogenic↗
PubMed2005

A comparison of foot/ground interaction during stair negotiation and level walking in young and older women.

Stair design and environmental conditions may play a role in slip accidents on stairs in the workplace, but little is known about the slip resistance requirements on stairs compared to level walking. Older adults have an increased risk of falling compared to younger adults and may be at greater risk during stair negotiation. The purpose of this study was to determine whether the ground reaction force profiles and peak required coefficient of friction (RCOF) differed between young and elderly women or between stair ascent, stair descent and overground walking. While there was a trend towards less risky stair descent behaviour in the older women in terms of their peak RCOF values during stair descent, the increased vertical loading rate in the older women may imply reduced dynamic balance control. The largest mean RCOF peaks occurred during stair ascent in both young and older women, but there were several overground walking trials in both groups and a few stair descent trials of the young women, which resulted in RCOF peaks greater than 0.5. These results should be considered when choosing stair surface materials, particularly in occupational and outdoor settings where the tread surfaces may become wet or contaminated.

Accidental Falls↗
PubMed2005

Foot clearance during stair descent: effects of age and illumination.

It is likely that many stair accidents result from a trip during stair negotiation, yet few studies have examined the exact nature of balance loss during falls on stairs. The purpose of this study was to investigate potential age-related differences in the minimum clearance of the foot during stair descent, and to explore whether the minimum foot clearance was affected by the available ambient lighting. Twelve young adults (24+/-3.3 years) and 10 older adults (73.7+/-1.9 years) participated in the study. The older adults had significantly greater within subject coefficients of variation compared to the young adults, and had a significantly larger number of minimum foot clearances which fell below 5 mm. While the young subjects increased their minimum clearance by 3.6 mm on average in response to a decrease in ambient lighting, the older adults maintained the same clearance over all stairs except one. These results suggest that the variability of minimum foot clearance, and lack of precautionary increases in foot clearance under reduced lighting may contribute to falls on stairs by the elderly.

Accidental Falls↗
PubMed2005

Diabetic peripheral neuropathy and depressive symptoms: the association revisited.

OBJECTIVE: We examined the association between severity of diabetic peripheral neuropathy and depressive symptoms and investigated the potential mediators of this association. RESEARCH DESIGN AND METHODS: The Hospital Anxiety and Depression Scale (HADS) was used to assess depressive symptoms in 494 patients (mean age 62 years; 70% male; 72% type 2 diabetic) with diabetic neuropathy diagnosed by the Neuropathy Disability Score (NDS) and the Vibration Perception Threshold (VPT). Diabetic neuropathy symptoms, activities of daily living (ADLs), and social self-perception were measured by the neuropathy and foot ulcer-specific quality-of-life instrument, NeuroQoL; perceptions of diabetic neuropathy symptom unpredictability and the lack of effective treatment were assessed by the revised Illness Perception Questionnaire. RESULTS: Both the NDS and VPT were significantly associated with the HADS after controlling for demographic and disease variables. Although diabetic neuropathy symptoms mediated this association, with unsteadiness being most strongly associated with HADS, the relationship between foot ulceration and depression was nonsignificant. The association between diabetic neuropathy symptoms and HADS was partially mediated by two sets of psychosocial variables: 1) perceptions of diabetic neuropathy symptom unpredictability and the lack of treatment control and 2) restrictions in ADLs and changes in social self-perception. CONCLUSIONS: These findings establish the association between diabetic neuropathy and depressive symptoms and identify potential targets for interventions to alleviate depressive symptoms in persons affected by diabetic peripheral neuropathy.

Activities of Daily Living↗
PubMed2005

Exercise and pharmacological countermeasures for bone loss during long-duration space flight.

Bone loss in the lower extremities and lumbar spine is an established consequence of long-duration human space flight. Astronauts typically lose as much bone mass in the proximal femur in 1 month as postmenopausal women on Earth lose in 1 year. Pharmacological interventions have not been routinely used in space, and countermeasure programs have depended solely upon exercise. However, it is clear that the osteogenic stimulus from exercise has been inadequate to maintain bone mass, due to insufficient load or duration. Attention has therefore been focused on several pharmacological interventions that have been successful in preventing or attenuating osteoporosis on Earth. Anti-resorptives are the class of drugs most commonly used to treat osteoporosis in postmenopausal women, notably alendronate sodium, risedronate sodium, zoledronic acid, and selective estrogen receptor modulators, such as raloxifene. There has also been considerable recent interest in anabolic agents such as parathyroid hormone (PTH) and teriparatide (rhPTH [1-34]). Vitamin D and calcium supplementation have also been used. Recent studies of kindreds with abnormally high bone mineral density have provided insight into the genetic regulation of bone mass. This has led to potential therapeutic interventions based on the LRP5, Wnt and BMP2 pathways. Another target is the RANK-L/osteoprotegerin signaling pathway, which influences bone turnover by regulating osteoclast formation and maturation. Trials using such therapies in space are being planned. Among the factors to be considered are dose-response relationships, bone quality, post-use recovery, and combination therapies--all of which may have unique characteristics when the drugs are used in space.

Aerospace Medicine↗
PubMed2004

Foot problems in diabetes: an overview.

Diabetes is the leading cause of nontraumatic lower-extremity amputations in the United States. Most amputations are preceded by an ulcer, and ulcers are costly in their own right. Most ulcers are neuropathic in etiology and plantar in location. They occur typically at sites of high mechanical loading because of repetitive trauma in people with loss of pain sensation. In an adequately perfused limb, such ulcers are not difficult to heal. When they are properly mechanically off-loaded, approximately 90% of these wounds heal in approximately 6 weeks. The reference standard off-loading device is the total contact cast, but other reasonably efficacious methods exist. Screening and implementation of preventive measures in the high-risk patient are highly recommended and can reduce the incidence of ulceration. All patients with diabetes should be screened annually for loss of protective sensation, with the 10-g Semmes-Weinstein monofilament being the easiest tool to use. Education to prevent complications should be implemented for all patients with loss of protective sensation.

Amputation, Surgical↗
PubMed2004

Pressure relief and load redistribution by custom-made insoles in diabetic patients with neuropathy and foot deformity.

OBJECTIVE: To study the effects of custom-made insoles on plantar pressures and load redistribution in neuropathic diabetic patients with foot deformity. DESIGN: Cross-sectional. BACKGROUND: Although custom-made insoles are commonly prescribed to diabetic patients, little quantitative data on their mechanical action exists. METHODS: Regional in-shoe peak pressures and force-time integrals were measured during walking in the feet of 20 neuropathic diabetic subjects with foot deformity who wore flat or custom-made insoles. Twenty-one feet with elevated risk for ulceration at the first metatarsal head were analysed. Load redistribution resulting from custom-made insoles was assessed using a new load-transfer algorithm. RESULTS: Custom-made insoles significantly reduced peak pressures and force-time integrals in the heel and first metatarsal head regions; pressures and integrals were significantly increased in the medial midfoot region compared with flat insoles. Custom-made insoles successfully reduced pressures in and integrals at the first metatarsal head in 7/21 feet, were moderately successful in another seven, but failed in the remaining seven. Load transfer was greatest from the lateral heel to the medial midfoot regions. CONCLUSIONS: Custom-made insoles were more effective than flat insoles in off-loading the first metatarsal head region, but with considerable variability between individuals. Most off-loading occurred in the heel (not a region typically at risk). The load transfer algorithm effectively analyses custom-made-insole action. RELEVANCE: Because similar insole modifications apparently exert different effects in different patients, a comprehensive evaluation of custom designs using in-shoe pressure measurement should ideally be conducted before dispensing insoles to diabetic patients with neuropathy and foot deformity.

Algorithms↗