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Biomedical subjects

H J Hermens

Publications and source records attributed to H J Hermens.

At least 37 records · Page 2Linked to original sources
PubMed2002

Application of a dual channel peroneal nerve stimulator in a patient with a "central" drop foot.

Dropped foot is a common mobility problem amongst patients after a cerebro vascular accident. The condition arises from paresis of the muscles that control the foot movement during the swing phase of gait. If the abnormal movement is not compensated for, it results in a significant decrease in the mobility and hence quality of life. Compensation for the drop foot can be achieved through the application of functional electrical stimulation. To date, in the clinical environment, the stimulation has been applied through electrodes placed on the skin over the common peroneal nerve, and using a single channel implant device. It is well known that with these techniques it is difficult to establish a balanced response of the foot. An implantable dual channel system for stimulation of the deep and superficial peroneal nerve has now been developed for patients with a drop foot following a stroke. By stimulation of the two branches of the common peroneal nerve separately it is possible to achieve a precisely balanced dorsal flexion and eversion of the foot. Stimulation occurs via small bipolar electrodes which are placed subepineural. After successful tests on animals we have now started the two channel peroneal nerve stimulator implantation in patients. The preliminary results of the first implants are presented.

Cerebrovascular Disorders↗
PubMed2002

Assessment of activities of daily living with an ambulatory monitoring system: a comparative study in patients with chronic low back pain and nonsymptomatic controls.

OBJECTIVE: The aim of this study was twofold: (1) to investigate whether differences in activities of daily living exist between patients with chronic low back pain (CLBP) and nonsymptomatic controls; (2) to investigate the day-to-day variability in daily activities. DESIGN: Physical activities were measured over a 24-hour period with an ambulant monitoring system. SETTING: Measurements were carried out in the subject's own environment. SUBJECTS: Forty-seven CLBP patients and 10 nonsymptomatic controls participated in this study. RESULTS: On group level, CLBP patients show a lower activity pattern compared with controls, especially during the evening. This is reflected in a lower walking step frequency during the day and evening, more lying time during the day and a lower physical activity level, less standing time and more lying time during the evening. The day-to-day variability in activity pattern is high and similar for both the patient and control group. CONCLUSION: The lower activity level especially found during the evening might indicate that patients need all their capacity to perform the tasks imposed during the day and as a consequence have less capacity left for their leisure time, in general the evening. This suggests the existence of an imbalance between the patient's physical capacity and the imposed environmental load. The large but similar day-to-day variability in activity pattern, which does not support the clinical findings of 'bad days' in CLBP patients, suggests the need for repeated measures.

Activities of Daily Living↗
PubMed2001

Differences in treatment outcome between subgroups of patients with chronic low back pain using lumbar dynamometry and psychological aspects.

OBJECTIVE: To investigate whether subgroups of patients with chronic low back pain show differences in treatment outcome, measured with the Roland Disability Questionnaire. (RDQ). SETTING: The study was carried out in a rehabilitation centre. SUBJECTS: Eighty-four patients with chronic low back pain participated in this study. INTERVENTION: Patients followed a multidisciplinary treatment programme that primarily targets physical aspects. DESIGN AND MAIN OUTCOME MEASURE: Based on pretreatment lumbar dynamometry results and Symptom Checklist (SCL-90) scores, patients were divided into subgroups. The dynamometry subgroups were: performances lower than healthy subjects (expected performance), performances comparable with those of healthy subjects (normal performance) and inconsistent performances (submaximal performance). The SCL-90 subgroups were: a total score of 'average' or lower compared with a population of chronic pain patients (low psychological score) and a total score of 'above average' or higher compared with this population (high psychological score). Patients answered the RDQ in the week before (RDQ1; n = 84) and after treatment (RDQ2; n = 78) to investigate whether the subgroups show differences in outcome expressed as the percentage change between RDQ2 and RDQ1, (%RDQ2-1). A %RDQ2-1 > or = 20% was classified as an improvement. RESULTS: Improvement on disability level > or = 20% is shown in 64% and 55% of the patients with 'normal' and 'expected' lumbar dynamometry performances and low psychological scores compared with only 33% and 25% of those with high psychological scores. Patients with submaximal performances show hardly any changes in disability level and there are no differences betweenthose with low psychological scores (14%) and those reporting high scores (0%). CONCLUSION: The fact that patient subgroups with differences in treatment outcome can be defined using lumbar dynamometry and psychological questionnaires suggests that these instruments might facilitate treatment indication in clinical practice.

Adult↗
PubMed2000

Cervical muscle dysfunction in the chronic whiplash associated disorder grade II (WAD-II).

STUDY DESIGN: In a cross-sectional study, surface electromyography measurements of the upper trapezius muscles were obtained during different functional tasks in patients with a chronic whiplash associated disorder Grade II and healthy control subjects. OBJECTIVES: To investigate whether muscle dysfunction of the upper trapezius muscles, as assessed by surface electromyography, can be used to distinguish patients with whiplash associated disorder Grade II from healthy control subjects. SUMMARY OF BACKGROUND INFORMATION: In the whiplash associated disorder, there is need to improve the diagnostic tools. Whiplash associated disorder Grade II is characterized by the presence of "musculoskeletal signs." Surface electromyography to assess these musculoskeletal signs objectively may be a useful tool. METHODS: Normalized smoothed rectified electromyography levels of the upper trapezius muscles of patients with whiplash associated disorder Grade II (n = 18) and healthy control subjects (n = 19) were compared during three static postures, during a unilateral dynamic manual exercise, and during relaxation after the manual exercise. Coefficients of variation were computed to identify the measurement condition that discriminated best between the two groups. RESULTS: The most pronounced differences between patients with whiplash associated disorder Grade II and healthy control subjects were found particularly in situations in which the biomechanical load was low. Patients showed higher coactivation levels during physical exercise and a decreased ability to relax muscles after physical exercise. CONCLUSIONS: Patients with whiplash associated disorder Grade II can be distinguished from healthy control subjects according to the presence of cervical muscle dysfunction, as assessed by surface electromyography of the upper trapezius muscles. Particularly the decreased ability to relax the trapezius muscles seems to be a promising feature to identify patients with whiplash associated disorder Grade II. Assessment of the muscle (dys)function by surface electromyography offers a refinement of the whiplash associated disorder classification and provides an indication to a suitable therapeutic approach.

Adult↗
PubMed2000

Surface EMG models: properties and applications.

After a general introduction on the kind of models and the use of models in the natural sciences, the main body of this paper reviews potential properties of structure based surface EMG (sEMG) models. The specific peculiarities of the categories (i) source description, (ii) motor unit structure, (iii) volume conduction, (iv) recording configurations and (v) recruitment and firing behaviour are discussed. For a specific goal, not all aspects conceivable have to be part of a model description. Therefore, finally an attempt is made to integrate the 'question level' and the 'model property level' in a matrix providing direction to the development and application of sEMG models with different characteristics and varying complexity. From this overview it appears that the least complex are models describing how the morphological muscle features are reflected in multi-channel EMG measurements. The most challenging questions in terms of model complexity are related to supporting the diagnosis of neuromuscular disorders.

Electromyography↗
PubMed2000

Development of recommendations for SEMG sensors and sensor placement procedures.

The knowledge of surface electromyography (SEMG) and the number of applications have increased considerably during the past ten years. However, most methodological developments have taken place locally, resulting in different methodologies among the different groups of users.A specific objective of the European concerted action SENIAM (surface EMG for a non-invasive assessment of muscles) was, besides creating more collaboration among the various European groups, to develop recommendations on sensors, sensor placement, signal processing and modeling. This paper will present the process and the results of the development of the recommendations for the SEMG sensors and sensor placement procedures. Execution of the SENIAM sensor tasks, in the period 1996-1999, has been handled in a number of partly parallel and partly sequential activities. A literature scan was carried out on the use of sensors and sensor placement procedures in European laboratories. In total, 144 peer-reviewed papers were scanned on the applied SEMG sensor properties and sensor placement procedures. This showed a large variability of methodology as well as a rather insufficient description. A special workshop provided an overview on the scientific and clinical knowledge of the effects of sensor properties and sensor placement procedures on the SEMG characteristics. Based on the inventory, the results of the topical workshop and generally accepted state-of-the-art knowledge, a first proposal for sensors and sensor placement procedures was defined. Besides containing a general procedure and recommendations for sensor placement, this was worked out in detail for 27 different muscles. This proposal was evaluated in several European laboratories with respect to technical and practical aspects and also sent to all members of the SENIAM club (>100 members) together with a questionnaire to obtain their comments. Based on this evaluation the final recommendations of SENIAM were made and published (SENIAM 8: European recommendations for surface electromyography, 1999), both as a booklet and as a CD-ROM. In this way a common body of knowledge has been created on SEMG sensors and sensor placement properties as well as practical guidelines for the proper use of SEMG.

Electrodes↗
PubMed1999

Validity and reproducibility of crutch force and heart rate measurements to assess energy expenditure of paraplegic gait.

OBJECTIVE: To determine the validity and reproducibility of heart rate (HR) and crutch force measurements to estimate energy expenditure during paraplegic walking. Usefulness of these outcome measures in comparative trials was assessed in terms of responsiveness. DESIGN: Cross-sectional validity was determined using one single (first) measurement. Longitudinal validity as well as reproducibility were calculated using repeated measurements. SETTING: Oxygen uptake and HR during steady state as well as axial crutch load were measured at subjects' self-selected walking speeds. PATIENTS: Ten subjects with thoracic-level spinal cord injury were included in the study. All subjects had considerable experience with ambulation in the advanced reciprocating gait orthosis (ARGO). MAIN OUTCOME MEASURES: Oxygen uptake (VO2, mL/min) and oxygen cost (EO2, mL/m) were used as criterion standards. Crutch peak force (CPF), crutch force time integral (CFTI), HR, and physiological cost index (PCI) were used to estimate energy expenditure. RESULTS: The PCI was found to be sensitive to detect differences between sessions in criterion standard (r = .86). Smallest detectable difference (ie, point where difference exceeds measurement error) ranged from approximately 15% for CPF to 33.7% and 41.8% for EO2 and PCI, respectively. CONCLUSIONS: Although PCI is expected to be a valid measure for within-patient differences in VO2, responsiveness was lower compared to EO2 and CPF. The limited number of patients who can be included in studies on paraplegic locomotion requires reproducible outcome measures. Therefore, CPF and EO2 are advocated in favor of PCI.

Adult↗
PubMed1999

Demand for and use of functional electrical stimulation systems and conventional orthoses in the spinal lesioned community of the UK.

The use of and demand for functional electrical stimulation (FES) systems and conventional orthoses in the spinal cord lesioned population was assessed. The assessment was conducted by a postal survey of the members of the spinal injury associations in the U.K. Out of all the respondents, only 2% had used an FES system for walking. In comparison, 13% had used some kind of orthosis. Of the small numbers who had used an FES system for walking, more than half had no functional walking abilities. The majority of orthosis users had some independent walking ability. The demand for walking improvements was high among the respondents although this was not matched by the demand for improved orthotic solutions. In conclusion, it would appear that there is a need for simple FES systems offering walking improvement to the incomplete spinal cord lesioned (SCI) subject.

Age Factors↗
PubMed1999

Distribution of psychological aspects in subgroups of chronic low back pain patients divided on the score of physical performance.

This study investigates whether different subgroups of chronic low back pain patients (CLBPs) differ in psychological aspects assessed with the Symptom Checklist (SCL-90) and the Multidimensional Pain Questionnaire (MPI-DLV). Four subgroups of CLBPs are discerned using the results of lumbar dynamometry: 1. Patients with performances lower than healthy subjects (expected performance; n = 45). 2. Patients with performances comparable to healthy subjects (normal performance; n = 18). 3. Patients with inconsistent test behaviour (submaximal performance; n = 6). 4. Patients with performances that could be either maximal or submaximal (gray-zone performance; n = 10). Significant differences in psychological aspects were found between patients with submaximal and patients with expected performances but not between patients with normal and patients with expected performances. All patients with submaximal performance report a high degree of psychological distress, in contrast to 30% of those with normal performance and 20% of those with expected performance. Because of the differences found in psychological aspects between the CLBP subgroups, it is thought that a physical screening together with a psychological screening provides better insight in the two aspects of the deconditioning syndrome and thus can give better treatment indications than a physical screening alone.

Adult↗
PubMed1999

Comparative trials on hybrid walking systems for people with paraplegia: an analysis of study methodology.

A new orthosis (SEPRIX) which combines user friendliness with low energy cost of walking has been developed and will be subject to a clinical comparison with conventional hip-knee-ankle-foot orthoses. In designing such comparative trials it was considered it may be worthwhile to use previous clinical studies as practical examples. A literature search was conducted in order to select all comparative trials which have studied two walking systems (hip-knee-ankle-foot orthoses) for patients with a complete thoracic lesion. Study population, intervention, study design, outcome measurement and statistical analyses were examined. Statistical power was calculated where possible. Of 12 selected studies, 7 were simple A-B comparisons, 2 A-B comparisons with a replication, 2 cross-over trials and 1 nonrandomised parallel group design, the last of which was considered internally invalid due to severe confounding by indication. All A-B comparisons were considered internally invalid as well, since they have not taken into account that a comparison of two orthoses requires a control for aspecific effects (like test effects) which may cause a difference. Statistical power could only be examined in 4 studies and the highest statistical power achieved in one study was 47%. It is concluded that statistical power was too low to be able to detect differences. Even analysis through interval estimation showed that the estimation of the difference was too imprecise to be useful. Since the majority of the surveyed papers have reported small studies (of only 4-6 patients), it is assumed that lack of statistical power is a more general problem. Three possibilities are discussed in order to enhance statistical power in comparative trials, i.e. multicentre studies, statistical pooling of results and improving the efficiency of study design by means of interrupted time series designs.

Equipment Design↗
PubMed1998

Relationships between isoinertial lumbar dynamometry parameters and demographic parameters in chronic low back pain patients.

The purpose of this study was to investigate which demographic parameters are most important in relation to lumbar dynamometry performance in patients with chronic low back pain (LBP). Forty-five chronic LBP patients participated in this study. Gender, age, weight and height were determined and a lumbar dynamometry measurement was carried out, using the Isostation B200. Student's t-test, ANOVA techniques and correlation coefficients were used to investigate the relationships between each demographic parameter and lumbar dynamometry performance. Stepwise multiple linear regression analyses were performed afterwards to determine which demographic parameters are most important in relation to lumbar dynamometry performance. Results indicate significant relationships (1) between gender, height, weight and all lumbar dynamometry parameters and (2) between age and three of the six isometric torque parameters. No significant relationship was found between age and maximum velocity parameters. Results of the stepwise multiple linear regression analyses show that the demographic parameters explain 27-47% of the variance in maximum isometric strength parameters and 19-25% of the variance in maximum velocity parameters. Gender is the most important demographic parameter, being related to nearly all maximum isometric torque parameters (percentage explained variance 6-37%) and height is the only important demographic parameter related to the velocity parameters (percentage explained variance 19-25%). Weight and age account for only a small amount of variance in lumbar dynamometry parameters (percentage explained variance 5-7%), meaning that these parameters are non-relevant predictors.

Adult↗
PubMed1998

Speed dependence of crutch force and oxygen uptake: implications for design of comparative trials on orthoses for people with paraplegia.

OBJECTIVE: To determine speed dependence of crutch force and oxygen uptake, and to discuss the implications of differences in self-selected walking speed between orthoses in a comparative trial. DESIGN: Cross-sectional comparison. SETTING: Treadmill experiments and gait laboratory experiments were performed at five and three different imposed walking speeds, respectively. PATIENTS: Five paraplegic subjects with lesions between T9 and T12 were included. All subjects had experience with ambulation using the advanced reciprocating gait orthosis (ARGO) as well as walking on a treadmill. MAIN OUTCOME MEASURES: Crutch force time integral (CFTI), crutch peak force on stance and swing side (CPFstance and CPFswing), oxygen uptake (VO2), oxygen cost (EO2). RESULTS: VO2, EO2, and CFTI were strongly dependent on walking speed. CPFstance and CPFswing were less dependent. However, depending on the clinically relevant difference that should be detected in a comparative trial, the peak forces can still be confounded by walking speed. CONCLUSION: CFTI, CPFswing, VO2, and EO2 should be adjusted for walking speed if differences in walking speed between orthoses are found, but this correction is relevant only if there is no effect modification. Such modification (different slopes between orthoses) cannot be excluded for the studied outcome measures. In addition, because determination of effect modification is difficult in small studies, standardization of walking speed, by means of a three-point design, is recommended.

Adult↗
PubMed1997

Reliability of lumbar dynamometry measurements in patients with chronic low back pain with test-retest measurements on different days.

Lumbar dynamometry is a potentially useful method for assessing the state of trunk muscles in low back pain (LBP) patients. The purpose of this study was to assess the reliability of lumbar dynamometry measurements in chronic LBP patients by conducting test-retest measurements on different days. Thirty-one men and 14 women with chronic LBP participated in this study. The experiments consisted of three sets of lumbar dynamometry measurements (Isostation B200) carried out on three different days with a 2- to 3-day interval. A standard protocol was administered to all subjects, consisting of a range-of-motion measurement about each axis, a 5 s maximum isometric trial about each axis and five dynamic repetitions about each axis against a resistance set at 25% and at 50% of the maximum isometric torque. Correlation coefficients and regression analysis were used to detect possible learning effects. One-way anova and regression analysis were used to assess the reliability of the measurements. High coefficients were found for the correlation between the first and second lumbar dynamometry measurements. Regression analysis showed that the differences between those measurements were not significant. This means that there was no learning effect operating between the first and second lumbar dynamometry measurements. One-way anova showed a reliability higher than 0.90 for the torque and velocity parameters. Reliability for the range-of-motion parameters was somewhat lower: between 0.76 and 0.94. Regression analysis showed no significant differences between the second and third measurements for the torque and velocity parameters. For range-of-motion parameters significant differences were found. From this study it can be concluded that the Isostation B200 provides reliable measures of torque and velocity parameters, but measures of the range-of-motion parameters are unreliable. No learning effect operates between the first and second lumbar dynamometry measurements, which means that a single measurement, with prior warming up and practice, is sufficient to assess the performance of the LBP patient.

Adult↗
PubMed1997

Energy storage and release of prosthetic feet. Part 1: Biomechanical analysis related to user benefits.

The energy storing and releasing behaviour of 2 energy storing feet (ESF) and 2 conventional prosthetic feet (CF) were compared (ESF: Otto Bock Dynamic Pro and Hanger Quantum; CF: Otto Bock Multi Axial and Otto Bock Lager). Ten trans-tibial amputees were selected. The study was designed as a double-blind, randomised trial. For gait analysis a VICON motion analysis system was used with 2 AMTI force platforms. A special measuring device was used for measuring energy storage and release of the foot during a simulated step. The impulses of the anteroposterior component of the ground force showed small, statistically non-significant differences (deceleration phase: 22.7-23.4 Ns; acceleration phase: 17.0-18.4 Ns). The power storage and release phases as well as the net results also showed small differences (maximum difference in net result is 0.03 J kg-1). It was estimated that these differences lead to a maximum saving of 3% of metabolic energy during walking. It was considered unlikely that the subjects would notice this difference. It was concluded that during walking differences in mechanical energy expenditure of this magnitude are probably not of clinical relevance. Ankle power, as an indicator for energy storage and release gave different results to the energy storage and release as measured with the special test device, especially during landing response. In the biomechanical model (based on inverse dynamics) used in the gait analysis the deformation of the material is not taken into consideration and hence this method of gait analysis is probably not suitable for calculation of shock absorption.

Adult↗
PubMed1997

Energy storage and release of prosthetic feet. Part 2: Subjective ratings of 2 energy storing and 2 conventional feet, user choice of foot and deciding factor.

This paper is the second part of a study on biomechanical and functional properties of prosthetic feet. The first part dealt with a biomechanical analysis related to user benefits. This part deals with subjective ratings and deciding factors for trans-tibial amputees using 2 energy storing feet (ESF) and 2 conventional feet (CF). The Otto Bock Dynamic Pro and Hanger Quantum feet were used as ESF and the Otto Bock Multi Axial and Otto Bock Lager feet were used as CF. Ten trans-tibial amputees, active walkers, without stump problems, were selected (mean age: 49 years old). The study was designed as a double-blind, randomised trial and for each foot there was a habituation period of 2 weeks. Two questionnaires were designed. (A) concerned information about the preference of the subjects and (B) concerned the order of importance of difference aspects concerning a prosthesis. Results indicated that no clear preference for either the ESF or the CF existed and that the individual preference is not related to age. The items 'ability to walk fast' and 'no fatigue during walking', score statistically significantly worse for the CF2. With the small contrast between the ESF and CF, in relation to energy storing capacities, the subjects cannot distinguish between the ESF and CF. The 'absence of stump pain' and 'stability while walking' are ranked as most important aspects concerning a prosthesis. The perception of stability is likely to be related to the level and kind of activities the subject performs.

Adult↗
PubMed1997

The influence of the reciprocal cable linkage in the advanced reciprocating gait orthosis on paraplegic gait performance.

A wide variety of mechanical orthoses is available to provide ambulation to paraplegic patients. Evaluation of energy cost during walking in each of these devices has been acknowledged as an important topic in this field of research. In order to investigate the benefits of a ballistic swing on gait performance in the Advanced Reciprocating Gait Orthosis (ARGO) a study was conducted in which the ARGO was compared with an orthosis with freely swinging legs. This Non Reciprocally linked Orthosis (NRO) was obtained by removing the reciprocal linkage in the subjects' own ARGOs. Subsequently, flexion/extension limits were mounted to permit adjustment of stride length. Six male paraplegic subjects with lesions ranging from T4 to T12 were included in the study. A single case experimental design (B-A-B-A) was conducted in order to improve internal validity. Biomechanical and physiological parameters were assessed and the subjects' preference for either ARGO or NRO was determined. It was found that large inter-individual differences produced insufficient evidence in this study to draw general conclusions about difference in energy expenditure between both orthoses. However, individual analysis of the results showed a reduction of oxygen cost (range: 4%-14%) in the NRO in T9 and T12 lesions, while oxygen cost in subjects with T4 lesions increased markedly (22% and 40%). It is concluded that patients with low level lesions could benefit in terms of oxygen lost from removing the reciprocal cable linkage in the ARGO. However, only one subject preferred the NRO for walking, whereas none of the subject chose the NRO for use in daily living activities. Removal of the reciprocal cable linkage in the ARGO may not be desirable for these patients.

Adult↗
PubMed1997

The influence of the reciprocal hip joint link in the Advanced Reciprocating Gait Orthosis on standing performance in paraplegia.

The effect of reciprocally linking the hip hinges of a hip-knee-ankle-foot orthosis on standing performance was studied in a comparative trial of the Advanced Reciprocating Gait Orthosis (ARGO) and an ARGO in which the Bowden cable was removed (A_GO). Six male subjects with spinal cord injury (SCI) at T4 to T12 level participated in the study, which was conducted using a single case experimental design. Standing balance, the ability to handle balance disturbances (standing stability), and the performance of a functional hand task during standing were assessed in both orthosis configurations in the order A_GO-ARGO-A_GO-ARGO. No significant differences with respect to standing performance were found for the two orthosis configurations. However, the results indicate that the crutch force needed for maintaining balance during various tasks, especially for quiet standing with two crutches, may be much higher in the orthosis without Bowden cable. Therefore, it is very likely that the reciprocal hip joint link in the ARGO provides a substantial and clinically relevant reduction of upper body effort required for standing under functional conditions.

Adult↗