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Biomedical subjects

T Mulder

Publications and source records attributed to T Mulder.

At least 19 recordsLinked to original sources
PubMed2004

Step characteristics during obstacle avoidance in hemiplegic stroke.

Whereas several animal studies have indicated the important role of the motor cortex in the control of voluntary gait modifications, little is known about the effects of cortical lesions on gait adaptability in humans. Obstacle avoidance tasks provide an adequate paradigm to study the adaptability of the stepping pattern under controlled, experimental conditions. In the present study, an exploratory assessment was made of the failure rate, the preferred stepping strategies (step lengthening vs step shortening), and the spatiotemporal stride characteristics (percentage increases in stride length, duration, and velocity of the crossing and postcrossing strides) during obstacle avoidance in 11 hemiplegic stroke patients and seven healthy controls. Patients were less successful in avoiding obstacles than controls (14% failure rate vs 0.5% in controls), independent of whether the affected or the unaffected leg led the obstacle avoidance. The number of failed trials increased systematically when the available response time became shorter. During successful trials, lengthening of the step was generally preferred over shortening. This bias towards step lengthening was more pronounced in stroke patients (step lengthening in 91% of the trials vs 75% in controls), irrespective of the side of obstacle presentation. For both groups, overall strategy preference did not adhere to a principle of minimal foot displacement, since step lengthening was used even if it would be more spatially efficient to shorten the step. No statistically significant group differences were found for the increases in length, duration, and velocity of the crossing and postcrossing strides. However, for a subgroup of more slowly walking patients, large percentage increases were found in crossing stride length, duration, and velocity. Similar results were obtained for the postcrossing stride, indicating that, for this subgroup of patients, restoration of the normal walking cadence was more difficult. Overall, no systematic differences were found between the affected and the unaffected leg in stroke patients with respect to failure rates, stepping strategies, or spatiotemporal measures of obstacle avoidance. The present findings suggest that the ability to adequately modify the stepping pattern in response to imposed spatiotemporal constraints is impaired in persons with stroke, especially when modifications have to be performed under time pressure. In addition, the stepping strategies employed by subjects with stroke are different from those found in controls, possibly to reduce the complexity of the avoidance maneuver and to enhance safety. Finally, unilateral cortical damage results in an impaired ability to avoid obstacles on both sides of the body, suggesting that the reduced ability of stroke patients to negotiate obstacles may be related to problems of a more general coordinative nature.

Adult↗
PubMed2004

Older women strongly prefer stride lengthening to shortening in avoiding obstacles.

In the present study the obstacle avoidance strategy during treadmill walking was investigated in ten young (aged 19-32) and ten older females (aged 65-78). Minimisation of displacement of the foot from its original landing position has been proposed to be the main criterion for the selection of alternate foot placement. Each participant performed 60 obstacle avoidance trials. Foot-obstacle configurations were varied in order to obtain both lengthening and shortening avoidance reactions. For each trial it was calculated how much lengthening and how much shortening of the stride was required minimally for successful avoidance. The difference between required lengthening and required shortening was expressed as a percentage of the control stride length and was used as a measure of minimal displacement. The behavior of young females was in agreement with the minimal displacement criterion. The older females, however, exhibited a strong preference for stride lengthening, even in situations in which stride shortening would be highly favorable. The explanation for the long step strategy preference of the older females is discussed in terms of age-related changes in decision-making, differences between young and older persons in the unobstructed gait pattern, and safety considerations.

Adult↗
PubMed2004

Speed related changes in muscle activity from normal to very slow walking speeds.

The study of neuromuscular activity at very slow walking speeds may lead to a better understanding of the mechanisms underlying speed regulation during walking, and may aid the interpretation of gait data in patients who walk slowly. Extreme reductions in walking speed will cause changes in locomotor task demands that may eventually result in modifications of the patterning of muscle activity that underlies walking. The aim of the present study was to investigate patterns of lower limb muscle activity during very slow walking (< 0.28 m s(-1)), and to study the neuromuscular gain functions that reflect the phase dependent effects of walking speed on electromyographic (EMG) amplitude. Nine healthy young adults walked at seven different walking speeds (1.39, 0.83, 0.28, 0.22, 0.17, 0.11, and 0.06 m s(-1)) while EMG was recorded from eight lower extremity muscles. Results showed that the phasing of muscle activity remained relatively stable over walking speeds despite substantial changes in its amplitude. However, between 1.39 and 0.28 m s(-1), epochs of Rectus femoris, Biceps femoris and Tibialis anterior activities were found that were typical for specific speed ranges. When walking speed decreased further to almost standing still (0.06 m s(-1)), negative gain values were found in Peroneus longus during midstance and Rectus femoris in late swing, indicating the emergence of new bursts of activity with decreasing walking speed. It is proposed that these extra activities may be attributed to increased demands on postural stability, and the altered dynamics of the swinging limb at very slow speeds.

Adult↗
PubMed2003

[Physiotherapy interventions in osteoporosis].

Osteoporosis is an increasing public health problem which ultimately causes fractures and a significant reduction in patient's health-related quality of life. In this context, physiotherapists are involved in a wide range of therapies related both to prevention and treatment of osteoporosis. The reduction of the risk of falling by elderly patients with osteoporosis is a very important goal for physiotherapists because it is known to significantly decrease fracture incidence. Indeed, exercise programs including elements of muscle strengthening and better body balance control have a positive effect on the risk of falling, hence reducing the incidence of fractures and increasing the health-related quality of life of osteoporotic patients. As a further consequence, the decreased fracture incidence has a key roll in reducing health care costs. Once a patient presents with an osteoporotic fracture, he may be assisted with various forms of passive, active-assisted and active therapies. This treatment will help reduce pain, increase patient's mobility and prevent the occurrence of additional fractures. In addition, a good and well-balanced education process regarding secondary osteoporosis prevention may also help to modify the behavior of patients and help to improve skeletal health in the longer term. The physiotherapist has definitively a major role to play in the interdisciplinary team aimed at preventing osteoporotic fractures in both primary and secondary prevention levels.

Accidental Falls↗
PubMed2001

[Psychiatric illness does not protect against a somatic disease].

In four patients, two women aged 68 and 73 years and two men aged 65 and 57 years, serious diseases were not recognised because of more prominent psychiatric symptoms. Three of the patients had malignancies and one was suffering from dehydration with a urinary tract infection and de novo diabetes mellitus. The patient with a meningioma recovered after surgery, the other three patients died despite treatment. Somatic diseases may not be recognised in patients with psychiatric illness because doctors may be more likely to ascribe the symptoms to a psychiatric cause. Patients may also present their symptoms in an unusual way. It is important not only to diagnose the psychiatric disease but also to check the patient's physical condition. This applies particularly to elderly patients, because they are more likely to have somatic diseases. Good education of psychiatrists in terms of somatic diseases remains important.

Aged↗
PubMed2001

Coordination between arm and leg movements during locomotion.

To evaluate the contrasting dynamical and biomechanical interpretations of the 2:1 frequency coordination between arm and leg movements that occurs at low walking velocities and the 1:1 frequency coordination that occurs at higher walking velocities, the authors conducted an experiment in which they quantified the effect of walking velocity on the stability of the frequency and phase coordination between the individual limb movements. Spectral analyses revealed the presence of 2:1 frequency coordination as a constant feature of the data in only 3 out of 8 participants at walking velocities ranging from 1.0 to 2.0 km/h, in spite of the fact that the eigenfrequencies of the arms were rather similar across participants. The degree of interlimb coupling, as indexed by weighted coherence and variability of relative phase, was lower for the arm movements and for ipsilateral and diagonal combinations of arm and leg movements than for the leg movements. Furthermore, the coupling between all pairs of limb movements was found to increase with walking velocity, whereas no clear signs were observed that the switches from 2:1 to 1:1 frequency coordination and vice versa were preceded by loss of stability. Therefore, neither a purely biomechanical nor a purely dynamical model is optimally suited to explain these results. Instead, an integrative model involving elements of both approaches seems to be required.

Adult↗
PubMed2001

Tea flavonoids: bioavailability in vivo and effects on cell signaling pathways in vitro.

The elucidation of the potential health benefits of tea beverage continues to be a focus of research in many laboratories. Beneficial effects of tea have been particularly evident in animal tumorigenesis models, with green and black tea frequently demonstrating similar effectivity. Human data are now emerging to support a beneficial role for tea in cardiovascular disease, but the data with respect to cancer risk at various sites remain inconclusive. The constituent flavonoids of green and black tea beverage are known to be potent antioxidants, and although this may be a major factor in explaining their biological activity, it appears that the gallated flavonoids in particular (e.g., epigallocatechin gallate and the gallated theaflavins) impact on a wide range of molecular targets that influence cell growth and more specifically pathways such as those involving angiogenesis. Data on the pharmacokinetic properties of tea flavonoids, primarily on the catechins and therefore related most closely to green tea, have provided indications of the plasma levels and circulating molecular forms that may be expected in humans following tea consumption. The structural complexity of black tea flavonoids, in particular the thearubigins, has hindered efforts to describe their bioavailability and to perform mechanistic studies. Recent studies on the effects of catechins and theaflavins on growth factor-, nuclear factor-kappaB-, and stress-mediated signal transductions are described in this review, where possible in relation to their bioavailability in vivo. These studies indicate that effects that may be relevant to both cancer and atherosclerosis are often observed at tea flavonoid levels that could realistically be encountered in vivo. However, more studies need to be performed using those molecular forms of tea flavonoids (methylated, sulfated, and glucuronidated conjugates) that are the major circulating species encountered following tea consumption. Such studies, combined with further human epidemiological and interventional data, should ultimately elucidate the full beneficial potential of tea beverage on human health.

Cell Cycle↗
PubMed2001

The regulation of fine movements in patients with Charcot Marie Tooth, type Ia: some ideas about continuous adaptation.

The flexibility of the human motor system is remarkable. Even when parts of the system are damaged, the output often remains optimal or near optimal. The neuromotor system is designed to keep the output optimal by shifting between input sources. This capability is termed the principle of continuous adaptation. This article describes an experiment in which patients suffering from a hereditary motor and sensory neuropathy, type 1a (Charcot Marie Tooth disease, type 1a), had to perform fine motor movements. We examined whether they were able to regulate these movements in spite of the fact that the somatosensory input and motor output was substantially impaired as a result of the chronic, slowly progressing neuropathy. It was predicted that these patients were able to perform fine movements as long as the movements were well known and over-learned. Furthermore, it was predicted that these patients would compensate for the loss of somatosensory information by becoming more dependent on vision. A second prediction was that the quality of the motor performance would break down when these patients had to perform a novel motor pattern. The performance of the patients (n=10) was contrasted with the performance of 20 healthy subjects. The results indicated that the patients, indeed, were able to perform the over-learned movements and that their performance deteriorated significantly when they had to perform a novel motor pattern. No indication, however, could be found for visual compensation.

Acceleration↗
PubMed2001

Adaptability and flexibility of the human motor system: implications for neurological rehabilitation.

This article stresses the plasticity of the adult sensorimotor cortex in response to various injuries or environmental changes. The dominant role of sensory input is discussed. A number of studies are presented that show how input may lead to learning and change. Learning is discussed in relation to recovery. It is shown how concepts from the field of motor control and learning may be used for improving neurological rehabilitation. Specific attention is given to the variability of input, the meaningfulness of input, and the role of the learning context. The learning context and the application context should have essential characteristics in common, otherwise transfer of learning will be non-optimal. It is argued that learning landscapes are necessary in order to treat patients in such a way that the learned skills are transferable to situations outside the hospital.

Humans↗
PubMed2000

Gait and electromyographic analysis of patients recovering after limb-saving surgery.

OBJECTIVE: Control of gait after limb-saving surgery.Design. Case series study. BACKGROUND: At the moment little is known about adaptations in patients' gait after limb-saving surgery. METHODS: Nineteen patients who underwent limb-saving surgery at least 1 yr earlier and 10 normal subjects were studied during treadmill walking. The main outcome measures were walking speed, step parameters and angular displacement of both legs and EMG of the biceps femoris, rectus femoris and medial gastrocnemius in the affected leg. RESULTS: Preferred walking speed in the patients was lower than in the controls (0.7 versus 1.1 m/s). Furthermore, stance phase of the non-affected leg was lengthened. All patients showed reduced stance phase knee flexion in the affected leg, while during the swing phase no difference was seen. The EMG signals of the rectus femoris and biceps femoris show changes, which are related to the location of surgery. CONCLUSIONS: The results showed that the gait pattern of the patients differed compared to normal gait. The reduced stance phase knee flexion in the hip group is based on a high degree of co-contraction between quadriceps and hamstring activity, while in the knee group this is based on the quadriceps avoidance pattern. The finding that there is still side-to-side asymmetry indicates that there is no complete reorganisation following the massive loss of input and output of the leg. It is possible that some reprogramming of the locomotor process occur. RELEVANCE: Gait and electromyographic analysis are essential for the quantitative assessments of the functional outcome in this type of surgery.

Adult↗
PubMed2000

Postural control in rheumatoid arthritis patients scheduled for total knee arthroplasty.

OBJECTIVE: To investigate the use of compensatory visual and attentional control strategies for standing balance in patients with rheumatoid arthritis (RA) with severe knee joint impairment. DESIGN: Experimental 2-group design. SETTING: Specialized clinic for orthopedics, rheumatology, and rehabilitation in The Netherlands. PARTICIPANTS: Eighteen patients without comorbidity (age range, 65 +/- 7.7 yr; 16 women, 2 men) from a consecutive sample of patients with RA scheduled for total knee arthroplasty; 23 controls of the same age group also were tested (13 women, 10 men). MAIN OUTCOME MEASURES: By means of a dual-plate force platform, the velocity of center of pressure (COP) fluctuations were analyzed in the anteroposterior and lateral sway directions during quiet standing with eyes open, eyes closed, and while performing a secondary attention-demanding arithmetic task. RESULTS: Patients showed an average 80% greater COP velocity in both directions of sway compared with controls. In addition, stability deteriorated substantially more in patients than controls when deprived of visual information, which was associated with the degree of knee destruction. The effect of the arithmetic task was small and similar in patients and controls. CONCLUSION: RA patients with severe knee joint impairment can have a substantial basic postural instability; their relatively high reliance on visual information suggests impaired sensory feedback from the lower limbs. Current research is aimed at determining whether these postural deficits can be improved by total knee replacement.

Activities of Daily Living↗
PubMed2000

Kinematic assessment of manual skill following functional hand surgery in tetraplegia.

To determine whether surgical key grip reinforcement actually leads to a better movement ability we developed a procedure for the kinematic analysis of manual skill following hand surgery in tetraplegia. The functional results of surgery in 5 cases were examined by the kinematic analysis of drawing movements using an electronic pen and a digitizer under 3 conditions: with eyes open, with eyes closed, and while performing a concurrent arithmetic task. Movement velocity and dysfluency (ie, the number of velocity changes per centimeter) were measured before and at several moments after surgery during subsequent rehabilitation. Both movement velocity and dysfluency showed good stability across repeated trials and were consistently affected by visual deprivation. Movement velocity showed a 39% increment between the first and last assessment. Although grip strength increased in all patients, it was not associated with the change of movement velocity. These results suggest that other factors (eg, deep sensibility, cognition, muscle coordination) play a critical role in the ability to use improved grip force for controlling drawing movements and emphasize the value of a kinematic assessment besides measuring isolated grip force in the evaluation of functional hand surgery.

Adult↗
PubMed2000

Muscular responses and movement strategies during stumbling over obstacles.

Although many studies have investigated reflexes after stimulation of either cutaneous or proprioceptive afferents, much less is known about responses after more natural perturbations, such as stumbling over an obstacle. In particular, the phase dependency of these responses and their relation to the stumbling behavior has received little attention. Hence response strategies during stumbling reactions after perturbations at different times in the swing phase of gait were studied. While subjects walked on a treadmill, a rigid obstacle unexpectedly obstructed the forward sway of the foot. All subjects showed an "elevating strategy" after early swing perturbations and a "lowering strategy" after late swing perturbations. During the elevating strategy, the foot was directly lifted over the obstacle through extra knee flexion assisted by ipsilateral biceps femoris (iBF) responses and ankle dorsiflexion assisted by tibialis anterior (iTA) responses. Later, large rectus femoris (iRF) activations induced knee extension to place the foot on the treadmill. During the lowering strategy, the foot was quickly placed on the treadmill and was lifted over the obstacle in the subsequent swing. Foot placement was actively controlled by iRF and iBF responses related to knee extension and deceleration of the forward sway. Activations of iTA mostly preceded the main ipsilateral soleus (iSO) responses. For both strategies, four response peaks could be distinguished with latencies of approximately 40 ms (RP1), approximately 75 ms (RP2), approximately 110 ms (RP3), and approximately 160 ms (RP4). The amplitudes of these response peaks depended on the phase in the step cycle. The phase-dependent modulation of the responses could not be accounted for by differences in stimulation or in background activity and therefore is assumed to be premotoneuronal in origin. In mid swing, both the elevating and lowering strategy could occur. For this phase, the responses of the two strategies could be compared in the absence of phase-dependent response modulation. Both strategies had the same initial electromyographic responses till approximately 100 ms (RP1-RP2) after perturbation. The earliest response (RP1) is assumed to be a short-latency stretch reflex evoked by the considerable impact of the collision, whereas the second (RP2) has features reminiscent of cutaneous and proprioceptive responses. Both these responses did not determine the behavioral response strategy. The functionally important response strategies depended on later responses (RP3-RP4). These data suggest that during stumbling reactions, as a first line of defense, the CNS releases a relatively aspecific response, which is followed by an appropriate behavioral response to avoid the obstacle.

Adult↗
PubMed1999

Widespread short-latency stretch reflexes and their modulation during stumbling over obstacles.

The present study investigated whether short-latency stretch reflexes are present during human stumbling reactions. While subjects walked on a treadmill, the forward sway of the foot was unexpectedly obstructed with an obstacle. All subjects showed reflex responses with average latencies of 34-42 ms in both the upper and the lower leg flexors and extensors of the obstructed leg. The amplitudes of these responses depended on the phase in the step cycle and were not strictly related to either the background activity of the corresponding muscles or variations in the perturbation. Hence, mechanisms at a premotoneuronal level might play a role in the active phase-dependent control of these responses. The coactivation of antagonists as well as the lack of obvious kinesiologic consequences following the responses suggest that the short-latency responses may generate joint stiffness. This may be a first line of defense in preparing for the functional reaction, which is generated by longer latency responses, in order to take appropriate action concerning the obstacle.

Adult↗
PubMed1999

Establishment of reference values for endocrine tests. II: Hyperprolactinemia.

BACKGROUND: In patients with hyperprolactinemia, the thyrotropin-releasing hormone (TRH) stimulation test is widely applied to distinguish prolactinoma from other causes of hyperprolactinemia. In the present study, we established reference values for the plasma concentration of prolactin (PRL) and its response to TRH. METHODS: Basal PRL and the PRL response to 400 micrograms TRH i.v. was determined in 50 subjects recruited from the general population, equally distributed according to sex and age between 20 and 69 years. PRL was determined by a fluoroimmunometric assay. Reference values are given as the observed range. RESULTS: Plasma concentrations of PRL were 4.0-25 micrograms/l (median: 10.0 micrograms/l) in women and 0.5-19.0 micrograms/l (median: 8.5 micrograms/l) in men (p = 0.11). The peak PRL concentration after stimulation with TRH was slightly higher in women (median: 51 micrograms/l) than in men (median: 41 micrograms/l; p = 0.04) and was reached at t = 20 min in all subjects. The relative increase in plasma PRL (median: 440%) did not show a statistically significant effect of age or sex. In 12 subjects (24%), the relative increase in plasma PRL was lower than 250%, which has traditionally been considered the minimum cutoff for a normal response. There were no effects of smoking and alcohol, but regular ingestion of liquorice was associated with lower basal (p = 0.03) and lower stimulated (p = 0.05) plasma concentrations of PRL. CONCLUSIONS: The present study provides reference values for basal and TRH-stimulated plasma concentrations of PRL.

Adult↗
PubMed1999

Neuropsychology and the relearning of motor skills following stroke.

Regaining independent mobility is one of the most important goals in physical therapy with patients suffering from the consequences of stroke. Both physical therapy and occupational therapy are learning processes in which the patient has to remaster old skills or has to learn novel skills. It is argued that the (re-)learning of motor control is a process in which motor aspects continuously interact with sensory and cognitive processes. It is therefore necessary that neuropsychological knowledge should be integrated in the therapy in order to create the most optimal situation for learning. In this article the most prominent neuropsychological consequences are described and suggestions are given as to how a therapist may use this knowledge to improve the therapy.

Cerebrovascular Disorders↗
PubMed1998

Neural control of locomotion: sensory control of the central pattern generator and its relation to treadmill training.

Many studies have shown that a special treadmill training is effective in restoring locomotor function in cats with a complete spinal lesion. In the last few years it has become possible to regain some locomotor activity in patients suffering from a spinal cord injury through an intense training on a treadmill, as in cats. The ideas behind this approach owe much to insights derived from studies on spinalized animals. The neural system responsible for the locomotor restoration in both cats and humans is thought to be located at spinal level and is referred to as the central pattern generator. The evidence for such a spinal central pattern generator is reviewed in part 1. An important element in the treadmill training for both spinal injured cats and humans is the provision of adequate locomotor related sensory input, which can possibly activate and/or regulate the spinal locomotor circuitry. This part of the review deals with the afferent control of the central pattern generator. Furthermore, the results of treadmill training for both cats and humans and their relation to sensory input are treated. These insights can possibly contribute to the design of a better treadmill training program for the rehabilitation of gait in spinal cord injured patients. Copyright 1998 Elsevier Science B.V. All rights reserved

Journal Article↗