Biomedical subjects

Peter H Veltink

Publications and source records attributed to Peter H Veltink.

12 recordsLinked to original sources

PubMed2006

Evaluation of instrumented shoes for ambulatory assessment of ground reaction forces.

Currently, force plates or pressure sensitive insoles are the standard tools to measure ground reaction forces and centre of pressure data during human gait. Force plates, however, impose constraints on foot placement, and the available pressure sensitive insoles measure only one component of force. In this study, shoes instrumented with two force transducers measuring forces and moments in three dimensions were evaluated. Technical performance was assessed by comparing force measurement and centre of pressure reconstructions of the instrumented shoes against a force plate. The effect of the instrumented shoes on gait was investigated using an optical tracking system and a force plate. Instrumented shoes were compared against normal shoes and weighted shoes. The ground reaction force measured with force plate and instrumented shoes differed by 2.2+/-0.1% in magnitude and by 3.4+/-1.3 degrees in direction. The horizontal components differed by 9.9+/-3.8% in magnitude and 26.9+/-10.0 degrees in direction. Centre of pressure location differed by 13.7+/-2.4mm between measurement systems. A MANOVA repeated measures analysis on data of seven subjects, revealed significant differences in gait pattern between shoe types (p</=0.05). A subsequent univariate analysis showed significant differences only in maximum ground reaction force but these could not be attributed to specific shoe types by pair-wise comparison. This study indicates that shoes instrumented with force transducers can be a valuable alternative to current measurement systems if accurate sensing of position and orientation of the force transducers is improved. They are applicable in ambulatory settings and suitable for inverse dynamics analysis.

Foot↗

PubMed2006

Comparison of electric stimulation methods for reduction of triceps surae spasticity in spinal cord injury.

OBJECTIVES: To compare the effect of 3 methods of electric stimulation to reduce spasticity of the triceps surae in patients with complete spinal cord injury (SCI) and to investigate the carryover effect. DESIGN: Placebo-controlled study with repeated measurements after the interventions. SETTING: Research department affiliated with a rehabilitation hospital in the Netherlands. PARTICIPANTS: Ten patients with a complete SCI were recruited from the outpatient population of the rehabilitation hospital. All subjects had American Spinal Injury Association grade A impairment scores, except for one, who had grade C. The patients had no voluntary triceps surae contractibility. INTERVENTIONS: Forty-five minutes of cyclic electric stimulation of the agonist, antagonist, or dermatome of the triceps surae or a placebo approach. MAIN OUTCOME MEASURES: Outcome measures were the Modified Ashworth Scale (MAS), clonus score, and the H-reflex and M wave (H/M) ratio. The electromyographic response to a stretch of the soleus over the whole range of motion was also determined. The magnitude and ankle angle at which the electromyographic response started were calculated. RESULTS: Stimulation of the agonist provided a significant reduction in the MAS compared with the placebo approach (P<.001). There was no significant change in the H/M ratio or the electromyographic response amplitude after any of the stimulation methods, whereas stimulation of the antagonist muscle resulted in a significant reduction in the ankle angle at which the electromyographic response started, compared with the placebo approach (P<.037). CONCLUSIONS: Triceps surae stimulation reduces the MAS for that specific muscle, whereas the angle at which the reflex starts changes after antagonist stimulation.

Adult↗

PubMed2005

Development of a new method for objective assessment of spasticity using full range passive movements.

OBJECTIVE: To develop a method for assessment of spasticity, in which the whole range of motion (ROM) at a wide variation of speeds is applied. DESIGN: Cross-sectional design to study construct validity. SETTING: Research department affiliated with a rehabilitation hospital in The Netherlands. PARTICIPANTS: Nine patients with complete spinal cord injury recruited from the rehabilitation hospital. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Thirty to 45 stretches over the whole ROM were applied to the triceps surae muscle at varying velocities measuring from 30 degrees to 150 degrees/s. Electromyographic responses were measured in order to assess reflex excitability. The torque over the ankle joint was measured during the whole stretch. The angle and velocity at which the reflex was initiated was also determined. RESULTS: The electromyographic responses increased significantly at increasing stretch velocities (P<.001). The applied maximum angles are reproducible (intraclass correlation coefficient, .81) and provide representative torque responses. CONCLUSIONS: The assessment method of spasticity using full range passive movements provides objective outcomes. The angular velocity is responsible for an exponential increase in amplitude of the electromyographic response.

Adult↗

PubMed2005

Compensation of magnetic disturbances improves inertial and magnetic sensing of human body segment orientation.

This paper describes a complementary Kalman filter design to estimate orientation of human body segments by fusing gyroscope, accelerometer, and magnetometer signals from miniature sensors. Ferromagnetic materials or other magnetic fields near the sensor module disturb the local earth magnetic field and, therefore, the orientation estimation, which impedes many (ambulatory) applications. In the filter, the gyroscope bias error, orientation error, and magnetic disturbance error are estimated. The filter was tested under quasi-static and dynamic conditions with ferromagnetic materials close to the sensor module. The quasi-static experiments implied static positions and rotations around the three axes. In the dynamic experiments, three-dimensional rotations were performed near a metal tool case. The orientation estimated by the filter was compared with the orientation obtained with an optical reference system Vicon. Results show accurate and drift-free orientation estimates. The compensation results in a significant difference (p < 0.01) between the orientation estimates with compensation of magnetic disturbances in comparison to no compensation or only gyroscopes. The average static error was 1.4 degrees (standard deviation 0.4) in the magnetically disturbed experiments. The dynamic error was 2.6 degrees root means square.

Acceleration↗

PubMed2005

Ambulatory measurement of ground reaction forces.

The measurement of ground reaction forces is important in the biomechanical analysis of gait and other motor activities. Many applications require full ambulatory measurement of these forces, but this is not supported by current measurement systems. We propose the use of two six-degrees-of-freedom force and moment sensors under each shoe, which enables the ambulatory measurement of ground reaction forces and centers of pressure (CoP). The feasibility of this method is illustrated by experimental results in a healthy subject, using a force plate as a reference. The ground reaction forces and CoP recordings show good correspondence when they are evaluated for forces above 40 N and when it is simply assumed that the sensors are flat on the ground when they are loaded. The root mean square (rms) difference of the magnitude of the ground reaction force over 12 gait trials was 15 +/- 2 N, corresponding to 1.9 +/- 0.3% of the maximum ground reaction force magnitude. The rms difference of the horizontal component of the ground reaction force was 3 +/- 2 N, corresponding to 0.4 +/- 0.2% of the maximum ground reaction force magnitude and to 2 +/- 1% of the maximum of the horizontal component of the ground reaction force. The rms distance between both CoP recordings is 2.9 +/- 0.4 mm, corresponding to 1.1 +/- 0.2% of the length of the shoe, when the trajectories are optimally aligned.

Equipment Design↗

PubMed2005

Gait impairments in a group of patients with incomplete spinal cord injury and their relevance regarding therapeutic approaches using functional electrical stimulation.

The purpose of this study is to determine the most important impairments affecting the gait pattern of the incomplete spinal cord injury (SCI) patient and the potential impact of their treatment. The study consists of two parts. Firstly, a survey amongst 16 professionals was done to find out the impact of the impairments in incomplete-SCI patients. Secondly, gait data from 21 individuals were analyzed to determine the most common impairments. Frequently observed and relevant impairments were: inadequate hip extension (occurrence 76%), limited hip flexion (52%), limited knee flexion (71%), excess of plantar flexion (76%), and impaired foot contact (52%). In conclusion, for gait improvement in incomplete spinal cord injured patients not only ankle movements must be treated, which is done frequently, but also hip extension/flexion and knee flexion are important for gait restoration. The impact on the gait and potential solutions of these impairments are discussed.

Adolescent↗

PubMed2004

Inclination measurement of human movement using a 3-D accelerometer with autocalibration.

In the medical field, accelerometers are often used for measuring inclination of body segments and activity of daily living (ADL) because they are small and require little power. A drawback of using accelerometers is the poor quality of inclination estimate for movements with large accelerations. This paper describes the design and performance of a Kalman filter to estimate inclination from the signals of a triaxial accelerometer. This design is based on assumptions concerning the frequency content of the acceleration of the movement that is measured, the knowledge that the magnitude of the gravity is 1 g and taking into account a fluctuating sensor offset. It is shown that for measuring trunk and pelvis inclination during the functional three-dimensional activity of stacking crates, the inclination error that is made is approximately 20 root-mean square. This is nearly twice as accurate as compared to current methods based on low-pass filtering of accelerometer signals.

Acceleration↗

PubMed2003

A model-based approach to stabilizing crutch supported paraplegic standing by artificial hip joint stiffness.

The prerequisites for stable crutch supported standing were analyzed in this paper. For this purpose, a biomechanical model of crutch supported paraplegic stance was developed assuming the patient was standing with extended knees. When using crutches during stance, the crutches will put a position constraint on the shoulder, thus reducing the number of degrees of freedom. Additional hip-joint stiffness was applied to stabilize the hip joint and, therefore, to stabilize stance. The required hip-joint stiffness for changing crutch placement and hip-joint offset angle was studied under static and dynamic conditions. Modeling results indicate that, by using additional hip-joint stiffness, stable crutch supported paraplegic standing can be achieved, both under static as well as dynamic situations. The static equilibrium postures and the stability under perturbations were calculated to be dependent on crutch placement and stiffness applied. However, postures in which the hip joint was in extension (C postures) appeared to the most stable postures. Applying at least 60 N x m/rad hip-joint stiffness gave stable equilibrium postures in all cases. Choosing appropriate hip-joint offset angles, the static equilibrium postures changed to more erect postures, without causing instability or excessive arm forces to occur.

Computer Simulation↗

PubMed2003

Static and dynamic evaluation of the influence of supplementary hip-joint stiffness on crutch-supported paraplegic stance.

Paraplegic persons can stand with hip-knee-ankle-foot orthoses (HKAFO) and crutches. However, current HKAFOs restrict body movement extensively, which may impede functional upper-body movements. A more compliant body support using a more compliant orthosis or well-controlled functional electrical stimulation system may increase freedom of movement to the user, but should not impede stability and required arm support. In the current study, we investigated the consequences of varying stiffness applied at the hip to postural stability and required crutch force during paraplegic stance. Experiments were performed on five paraplegic persons with spinal cord lesions varying from T1 to T12. Static postures and dynamic responses to perturbations were tested for varying hip stiffness and crutch placements. The minimal hip-joint stiffness for stable stance appeared to depend on lesion level. In contrast to the predictions of a previous modeling study, no statistically significant influences of hip-joint stiffness or crutch-to-foot distance on posture and applied crutch forces were found. It is hypothesized that the main reasons of this discrepancy are the active upper-body efforts the paraplegic HKAFO users are still able to exert and the remaining flexibility of the upper trunk and shoulder region, which is present despite the restrictions of the orthosis.

Computer Simulation↗

PubMed2002

Accelerometer and rate gyroscope measurement of kinematics: an inexpensive alternative to optical motion analysis systems.

A general-purpose system to obtain the kinematics of gait in the sagittal plane based on body-mounted sensors was developed. It consisted of four uniaxial seismic accelerometers and one rate gyroscope per body segment. Tests were done with 10 young healthy volunteers, walking at five different speeds on a treadmill. In order to study the system's accuracy, measurements were made with an optic, passive-marker system and the body-mounted system, simultaneously. In all the comparison cases, the curves obtained from the two systems were very close, showing root mean square errors representing <7% full range in 75% of the cases (overall mean 6.64%, standard deviation 4.13%) and high coefficients of multiple correlation in 100% of cases (overall mean 0.9812, standard deviation 0.02). Calibration of the body-mounted system is done against gravity. The body-mounted sensors do not hinder natural movement. The calculation algorithms are computationally demanding and only are applicable off-line. The body-mounted sensors are accurate, inexpensive and portable and allow long-term recordings in clinical, sport and ergonomics settings.

Acceleration↗

PubMed2002

Standing balance evaluation using a triaxial accelerometer.

This paper presents a new inherently triaxial accelerometer-based system for determining the ability to maintain balance while standing. In this study, the accelerometer was placed at the back of the subject at the approximate height of the centre of mass. The data were processed to obtain five performance parameters. Paired t-tests indicated that the accelerometer measurements were able to distinguish between the different test conditions as well as or better than simultaneous AMTI force platform measurements (P < or = 0.05). The accelerometer system is fully portable, independent of inclination in space, low-cost and allows long term measurements of standing balance.

Electrophysiology↗

PubMed2002

The optimal stimulation pattern for skeletal muscle is dependent on muscle length.

Stimulation patterns can be optimized by maximizing the force-time integral (FTI) per stimulation pulse of the elicited muscle contraction. Such patterns, providing the desired force output with the minimum number of pulses, may reduce muscle fatigue, which has been shown to correlate to the number of pulses delivered. Applications of electrical stimulation to use muscle as a controllable biological actuator may, therefore, be improved. Although muscle operates over a range of lengths, optimized patterns have been determined only at optimal muscle length. In this study, the patterns with up to four pulses that produced the highest isometric FTI were determined at 10 muscle lengths for 11 rabbit tibialis anterior muscles. The interpulse intervals (IPIs) used ranged from 4 to 54 ms. At high muscle length, the optimal stimulation pattern consisted of an initial short IPI (doublet) followed by longer IPIs, in agreement with previous studies. However, at low length, the third pulse still elicited more than linear summation (triplet); furthermore, the relative enhancement of the FTI per pulse was considerably larger at low length than at high length, suggesting that optimal stimulation patterns are length dependent.

Animals↗