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Biomedical subjects

P R Cavanagh

Publications and source records attributed to P R Cavanagh.

At least 55 records · Page 3Linked to original sources
PubMed1996

Ground reaction forces during locomotion in simulated microgravity.

BACKGROUND: Significant losses in bone density and mineral, primarily in the lower extremities, have been reported following exposure to weightlessness. Recent investigations suggest that mechanical influences such as bone deformation and strain rate may be critically important in stimulating new bone formation. HYPOTHESIS: It was hypothesized that velocity, cadence, and harness design would significantly affect lower limb impact forces during treadmill exercise in simulated zero-gravity (0G). METHODS: A ground-based hypogravity simulator was used to investigate which factors affect limb loading during tethered treadmill exercise. A fractional factorial design was used and 12 subjects were studied. RESULTS: The results showed that running on active and passive treadmills in the simulator with a tethering force close to the maximum comfortable level produced similar magnitudes for the peak ground reaction force. It was also found that these maximum forces were significantly lower than those obtained during overground trials, even when the speeds of locomotion in the simulator were 66% greater than those in 1G. Cadence had no effect on any of the response variables. The maximum rate of force application (DFDTmax) was similar for overground running and exercise in simulated 0G, provided the "weightless" subjects ran on a motorized treadmill. CONCLUSIONS: These findings have implications for the use of treadmill exercise as a countermeasure for hypokinetic osteoporosis. As the relationship between mechanical factors and osteogenesis becomes better understood, results from human experiments in 0G simulators will help to design in-flight exercise programs that are more closely targeted to generate appropriate mechanical stimuli.

Adult↗
PubMed1995

The use of running shoes to reduce plantar pressures in patients who have diabetes.

We compared the plantar pressures generated by walking in leather-soled Oxford-style shoes and by walking in inexpensive running shoes with those generated by walking in thin socks on a hard surface for thirty-nine individuals (thirteen who had diabetes and neuropathy, and thirteen who had diabetes without neuropathy, and thirteen who had neither diabetes nor neuropathy [controls]). Except for two anatomical regions, the plantar pressure associated with the Oxford-style shoes were not different from those associated with walking without shoes. In comparison, the inexpensive running shoes relieved plantar pressure in the forefoot and heel by a mean (and standard deviation) of 31 +/- 9.1 per cent, with the most relief occurring in the feet that had the highest pressures when they were unshod. There were significant reductions in pressure in all regions of the foot except for the midfoot (p < 0.01), and there were no significant differences between the groups. Individuals who have insensate feet should be discouraged from wearing leather-soled Oxford-style shoes because of the risk of ulceration due to elevated plantar pressures. Inexpensive running shoes should be viewed as the very minimally acceptable choice for footwear for these individuals if the feet are free of deformity.

Adult↗
PubMed1994

Assessment and management of foot disease in patients with diabetes.

Limb- or life-threatening complications in patients with diabetes can be prevented with an integrated, multidisciplinary approach. Most patients seen in clinical practice are in the early stages of the disease process. Glycemic control retards the progression of neuropathy, which is the most important risk factor for ulceration. Early detection of the loss of protective sensation and implementation of strategies to prevent ulceration will reduce the rates of limb-threatening complications. Clinicians should routinely examine the feet of diabetic patients. Education in foot care, proper footwear, and close follow-up are required to prevent or promptly detect neuropathic injury. If ulceration occurs, removal of pressure from the site of the ulcer and careful management of the wound will allow healing in most cases. The failure to heal despite these measures should prompt a search for associated arterial insufficiency. If infection is present, appropriate antimicrobial therapy combined with immediate surgical intervention, including revascularization when necessary, will increase the chances of saving the limb. With this comprehensive approach, it is possible to achieve the goal of a 40 percent decrease in amputation rates among diabetic patients by the year 2000.

Anti-Bacterial Agents↗
PubMed1994

Foot inversion-eversion and knee kinematics during walking.

The purpose of this study was to monitor selected aspects of the three-dimensional kinematics of the knee during walking with regular shoes and with modified shoes that induced either pronation or supination of the foot. Steinmann traction pins were inserted into the right tibia and femur of five adult men who had apparently normal lower extremities. Target clusters mounted onto the pins were filmed by four cine cameras operating at 100 frames/sec. Two trials per subject were analyzed for each of the three experimental conditions: regular running shoes, running shoes with a 10 degree valgus wedge, and running shoes with a 10 degree varus wedge. The different types of footwear induced only minor kinematic changes at the knee during the stance phase of walking. The angular patterns of the tibiofemoral joint were modified by less than 1 degree, whereas the translatory patterns were altered by 2 mm. Immediately following foot-strike, the valgus-wedge shoes caused the tibia to rotate internally 4 degrees more than the varus-wedge shoes, but at the tibiofemoral joint no consistent differences in the pattern of internal-external rotation between normal and modified footwear were measureable. These findings suggest that, in the healthy lower extremity, increased internal and external tibial rotation is resolved at the hip joint, with changes at the tibiofemoral joint that barely are detectable with the techniques used in this study.

Adult↗
PubMed1994

Locomotion in a rotating space station: a synthesis of new data with established concepts.

Despite technical problems associated with designing a rotating space station it is still thought that such a device may provide a more tolerable work environment and prevent some of the physiological changes that currently pose a threat to long-duration space missions. In the present analysis four case studies are presented and the results show that centrifugal and Coriolis effects could hinder one's ability to walk or run in a natural way in such an environment. In a rotating station that has a nominal 'G-level' equal to that on earth it can be shown that a person running at 3.8 m s -1 could experience foot 'heaviness' effects that range from 1 to 3 g and fore-aft foot 'forces' that range fom -0.5 to +0.5 g. In contrast the hip region could sense a relatively constant 'force' equal to 2 g. With regard to the body as a whole there would be 'weight changes' that depended on the direction of gait. While these conditions imply that locomotion in a rotating space station would be different from normal gait, it is likely that given sufficient training, astronauts could learn optimal strategies to account for centrifugal and Coriolis effects on individual body segments. The learning process would also entail developing strategies on which route to take when moving from one location to another, since in many cases the shortest route would not be the least energy consuming. Such training would be justified if it were shown that artificial gravity was an effective countermeasure to the problems of muscle atrophy and bone loss.

Coriolis Force↗
PubMed1994

Postural instability in patients with diabetic sensory neuropathy.

OBJECTIVE: Recent survey evidence suggests that sensory ataxia due to diabetic neuropathy may be a more frequent and serious problem than is commonly recognized. This view is further supported by research that confirms the major contribution of the somatosensory system to the control of posture. We therefore sought to determine the effects of significant diabetic distal symmetrical polyneuropathy on the control of posture. RESEARCH DESIGN AND METHODS: Fifty-one subjects, divided into three groups, participated in this study. Seventeen had diabetes and significant sensory neuropathy, 17 had diabetes and no neuropathy, and 17 had neither diabetes nor neuropathy. The subjects were matched across groups, and stringent exclusion criteria were applied. Postural stability during quiet standing was measured using a force platform. In addition to electrophysiological and quantitative sensory tests of neuropathy, a number of physical and functional characteristics were measured for all subjects. RESULTS: Postural instability was found to be significantly associated with sensory neuropathy, but not with diabetes per se. Patients with sensory neuropathy demonstrated between 66 and 117% more instability than did control subjects (depending on the testing condition). Based on multiple linear regression analyses, the most significant correlates of instability were the quantitative sensory measures of neuropathy and age. CONCLUSIONS: The loss of sensory perception secondary to diabetic distal symmetrical sensory neuropathy has a markedly detrimental effect on postural stability. The deficit is greatest when visual or vestibular cues are absent or degraded. Patients with neuropathy need to be informed of the postural consequences of this condition to limit the potential morbidity caused by falls.

Aging↗
PubMed1994

Radiographic abnormalities in the feet of patients with diabetic neuropathy.

OBJECTIVE: To investigate the prevalence of radiographic bone and joint abnormalities in the feet of diabetic patients. RESEARCH DESIGN AND METHODS: In a blinded randomized study, 94 diabetic patients with peripheral neuropathy (54 with a history of foot ulcers) and 43 non-neuropathic patients were drawn at random from the data base of a large university diabetes clinic in the United Kingdom. Fifty nondiabetic age-matched control subjects also were studied. Lateral and dorsi-plantar weight-bearing plain radiographs of the foot and ankle were taken by a single radiographer. Abnormalities in the bones and joints were determined according to a structured reading of the radiographs by a single radiologist. RESULTS: Diabetes per se resulted in no excess of bony abnormality. Diabetic patients with neuropathy had significantly more radiographic abnormalities of the bones and joints than non-neuropathic and age-matched nondiabetic control subjects. However, except for periosteal reaction, this was predominantly caused by an excess of abnormalities in diabetic patients with a history of foot ulceration. Traumatic fractures (most previously unrecognized) were found in 12 (22%) of the 54 neuropathic patients with previous foot ulceration, and 9 (16%) patients who had experienced foot ulcers exhibited characteristic Charcot changes. CONCLUSIONS: These results suggest that bony abnormalities, particularly Charcot changes and traumatic fractures, are more frequent than previously recognized in neuropathic diabetic patients, especially in those with a history of foot ulceration. Early recognition of bony abnormality and appropriate treatment may prevent progression of foot deformity and thereby reduce the morbidity caused by ulceration or reulceration.

Adult↗
PubMed1993

Medial arterial calcification in the feet of diabetic patients and matched non-diabetic control subjects.

The prevalence and distribution of medial arterial calcification was assessed in the feet of four subject groups; 54 neuropathic diabetic patients with previous foot ulceration (U), median age 60.5 (50.5-67 interquartile range) years, duration of diabetes 19.5 (9.9-29.9) years; 40 neuropathic diabetic patients without a foot ulcer history (N), age 68 (62-73) years, duration of diabetes 14.0 (8.0-28.0) years; 43 non-neuropathic diabetic patients (NN), age 60.5 (52-68.5) years, duration of diabetes 14.0 (8.0-28.0) years and 50 non-diabetic control subjects, age 62.5 (53.7-70) years. A single radiologist graded medial arterial calcification as absent, mild or severe, at the ankle, hind-foot, mid-foot, metatarsals and toes on standardised plain lateral and antero-posterior foot radiographs taken by a single radiographer. Diabetes history, vibration perception threshold, ankle systolic pressure and serum creatinine were also assessed. Medial arterial calcification was significantly greater (total score 18 [3-31]) in neuropathic diabetic patients with previous ulceration (U vs N p < 0.01, U vs NN p < 0.001). Non-neuropathic diabetic patients did not have significantly higher arterial calcification scores than age-matched non-diabetic control subjects. Medial arterial calcification correlated with vibration perception threshold (r = 0.35), duration of diabetes (r = 0.32) and serum creatinine (r = 0.41), (all p < 0.01). Logistic regression models showed vibration perception and duration of diabetes to predict the probability of any calcification. Serum creatinine level was added to predict severe calcification.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1993

Ulceration, unsteadiness, and uncertainty: the biomechanical consequences of diabetes mellitus.

Diabetes mellitus, which results from a failure of the endocrine system to control blood glucose levels within normal limits, affects approximately 15% of the population over the age of 65 in developed countries. Between 20-50% of people with diabetes for more than 10 years will experience symmetrical distal sensory neuropathy resulting in a progressive, distal to proximal, loss of sensation in the lower extremities. The most common consequence is plantar ulceration that too often results in partial or total amputation of the foot. While neuropathy is a major permissive factor, plantar ulcers occur at locations of high plantar pressures. The measurement of pressure using tools developed and refined in the field of biomechanics has been shown to be a valuable asset to the management of the foot at risk for ulceration. In particular, the use of in-shoe measuring techniques has the potential to revolutionize the prescription of therapeutic footwear. Biomechanical techniques have also helped to evaluate other consequences of diabetic neuropathy on the foot such as callus formation, foot deformity, limited joint mobility and bony abnormalities. The reduction of afferent information from the lower extremities implies a lack of active feedback thought to be necessary for the control of human movements such as posture and gait. Our results show that diabetic neuropathy results in a significant increase in sway during standing that is not compensated for by other sensory systems. The study of the sagittal plane movements of the same individuals walking on a treadmill showed little effect on the kinematic control of gait when compared to age matched nonneuropathic control groups. This may indicate the dominance of efferent input over afferent feedback during gait. We believe that the study of the biomechanical consequences of diabetes can act as a model for many other diseases that have yet to come under the scrutiny of a multidisciplinary team.

Biomechanical Phenomena↗
PubMed1993

Simulating reduced gravity: a review of biomechanical issues pertaining to human locomotion.

In the decade preceding Apollo missions to the Moon, extensive studies were conducted on human locomotion in reduced gravity. These investigations focused primarily on issues of maneuverability and energy expenditure and not on musculoskeletal loading, which is of more interest to planners of long-duration space missions. The techniques have included water immersion, parabolic aircraft flights, supine and erect cable suspension and centrifugal methods. The practical implications of the findings from these studies are: 1) the present shuttle treadmill running surface would not suffice if one wanted to run with a natural style at levels greater than 0.6 G; 2) in terms of attempting to replicate typical ground reaction force profiles during locomotor exercise at reduced gravity levels, it appears as though it is easier to match the peak rates of change of force (maxDFDT) than it is to match values for the peak force magnitudes (maxGRF).

Biomechanical Phenomena↗
PubMed1993

The computer era in gait analysis.

This article traces the history of the use of computers in the analysis of human gait. Following a brief retrospective review of the precomputer era, the topics of motion, force, and pressure analysis using computers are discussed. The need for careful justification of clinically applied techniques is stressed throughout, and some future trends are anticipated.

Foot↗
PubMed1992

Three-dimensional kinematics of the human knee during walking.

Three-dimensional kinematics of the tibiofemoral joint were studied during normal walking. Target markers were fixed to tibia and femur by means of intra-cortical traction pins. Radiographs of the lower limb were obtained to compute the position of the target markers relative to internal anatomical structures. High-speed cine cameras were used to measure three-dimensional coordinates of the target markers in five subjects walking at a speed of 1.2 m s-1. Relative motion between tibia and femur was resolved according to a joint coordinate system (JCS). The measurements have identified that substantial angular and linear motions occur about and along each of the JCS axes during walking. The results do not, however, support the traditional view that the so-called 'screw home' mechanism of the knee joint operates during gait.

Adult↗
PubMed1992

The effects of visual factors and head orientation on postural steadiness in women 55 to 70 years of age.

This study was designed to establish reference data for the effects of head position and visual conditions on the standing posture of healthy women ages 55 to 70. Center of pressure (CoP) data were analyzed using ANOVA models. Total CoP displacement was 45% greater (significant, p less than .05) when the subjects stood with their heads back and their eyes closed, as compared to standing looking straight ahead. Visual surrounds consisting of vertical visual cues resulted in less postural sway (PS) than surrounds made of horizontal visual cues (significant, p less than .05 for anteroposterior CoP range). Experimentally reduced visual acuity resulted in greater PS, while changes in ambient lighting and spatial frequency of visual cues affected PS minimally. These results suggest that a reduction in the height of shelving, and the provision of high-contrast visual cues and vertical geometric patterns are potential intervention strategies to optimize vestibular sensory input and visual orientational cues for the maintenance of stability during stance.

Aged↗
PubMed1992

Problems with gait and posture in neuropathic patients with insulin-dependent diabetes mellitus.

Peripheral neuropathy secondary to diabetes mellitus is believed to cause postural instability and uncoordinated gait, although this is not well documented. Two groups of patients from the Pittsburgh Epidemiology of Diabetes Complications Study, matched for age and duration of Type 1 diabetes, but with significantly different vibratory sensation thresholds as determined by Vibratron II testing, were therefore surveyed. The mean ages were 32.9 and 31.9 years and durations of diabetes were 22.0 and 18.8 years for the neuropathic and control groups, respectively. Patients provided details of fall injuries, and perception of safety during standing and walking. Multiple linear and logistic regression models were used to account for potentially associated variables such as gender, retinopathy, and duration of diabetes. The neuropathic group had adjusted odds ratios for reported injuries during gait of 15.0 relative to the control group (95% confidence intervals 1.04-216.59). The neuropathic group also reported significantly lower scores (less safe, p = 0.004) than the control group on perceived safety in unusual conditions. It is concluded that peripheral neuropathy has an effect on gait and posture which is clinically significant and that this effect merits further biomechanical study in neuropathic patients.

Accidental Falls↗
PubMed1992

A biomechanical perspective on exercise countermeasures for long term spaceflight.

Many systems of the body undergo adaptation on exposure to hypogravity, with the lower extremity skeleton experiencing considerable mineral loss during relatively short periods of hypogravic exposure. To date, a variety of countermeasures have had limited success in preventing demineralization, though it is now accepted that mechanical deformation is critical for bone homeostasis on Earth. In the present study, three exercises under active consideration for use in the Space Station were compared in 1 G in terms of the peak loads and rates of change of load elicited under the feet. Peak loading rates were in the ratio of 34.7:1.9:1 for running, rowing, and cycling, respectively. With regard to peak foot loads, the corresponding values were in the ratio of 5.3:1:1.2. These results suggest that exercise during spaceflight must be considered from both biomechanical and physiological perspectives if optimal response is to be obtained.

Adult↗