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Biomedical subjects

R Aissaoui

Publications and source records attributed to R Aissaoui.

12 recordsLinked to original sources
PubMed2004

A 3D generic inverse dynamic method using wrench notation and quaternion algebra.

In the literature, conventional 3D inverse dynamic models are limited in three aspects related to inverse dynamic notation, body segment parameters and kinematic formalism. First, conventional notation yields separate computations of the forces and moments with successive coordinate system transformations. Secondly, the way conventional body segment parameters are defined is based on the assumption that the inertia tensor is principal and the centre of mass is located between the proximal and distal ends. Thirdly, the conventional kinematic formalism uses Euler or Cardanic angles that are sequence-dependent and suffer from singularities. In order to overcome these limitations, this paper presents a new generic method for inverse dynamics. This generic method is based on wrench notation for inverse dynamics, a general definition of body segment parameters and quaternion algebra for the kinematic formalism.

Acceleration↗
PubMed2001

Analysis of pressure distribution at the body-seat interface in able-bodied and paraplegic subjects using a deformable active contour algorithm.

In this paper, a semi-automatic method for segmenting pressure distribution image-based data at the body-seat interface is presented. The purpose of this work was to estimate the surface and the load supported by the ischial tuberosity (IT) region. The proposed method involves three steps: (1) detecting the IT region using a pressure-distribution image gradient; (2) estimating the contour of the IT region by an iterative active contour algorithm and finally (3) estimating the percentage of the surface and the weight-bearing of the IT region in a group of able-bodied (AB) and spinal-cord injury (SCI) subjects. It was found in this study that the weight bearing on the IT for the spinal-cord injured group is distributed on half the surface in comparison with the AB group or the powered wheelchair users groups. The findings of this study provide insights concerning pressure distribution in sitting for the paraplegic and able-bodied.

Adult↗
PubMed2001

Effect of seat cushion on dynamic stability in sitting during a reaching task in wheelchair users with paraplegia.

OBJECTIVES: To examine the effects of seat cushions on dynamic stability in sitting during a controlled reaching task by wheelchair users with paraplegia. DESIGN: A randomized, controlled test. SETTING: Rehabilitation center. PARTICIPANTS: Nine wheelchair users with paraplegia. INTERVENTIONS: Three types of cushions--an air flotation, a generic contoured, and a flat polyurethane foam--were tested during a controlled reaching task in ipsilateral and contralateral directions, at 45 degrees from the sagittal plane in the anterolateral direction. Center of pressure (COP) coordinates were monitored by using a pressure measurement system as well as a force platform under seat. MAIN OUTCOME MEASURES: Trajectory of COP, maximal distance covered by COP, maximal velocity of COP; and the index of asymmetry between right and left maximal pressure under ischial tuberosities. RESULTS: The generic contoured cushion allowed the COP to cover significantly (p <.02) a larger distance (81 +/- 28mm) when compared with the air flotation (63 +/- 25mm) or the flat foam (61 +/- 29mm) cushions. The COP velocity was significant (p <.05) for the generic contoured cushion (.14 +/-.05m/s) versus the air flotation (.10 +/-.04m/s) or the flat-foam (.10 +/-.03m/s) cushions. The index of asymmetry was higher for the generic contoured and the flat foam cushions. During reaching, maximal pressure under ipsilateral ischial tuberosity was significantly higher for the flat foam (275 +/- 70mmHg) and the generic contoured (235 +/- 81mmHg) cushions, when compared with the air flotation cushion (143 +/- 51mmHg). CONCLUSION: Seat cushions can significantly affect sitting balance during reaching tasks. This study provided an objective method to assess the dynamic stability of wheelchair users when they perform activities of daily living requiring reaching. These findings have implications for wheelchair seating recommendations, especially seat cushion selection.

Activities of Daily Living↗
PubMed2001

Analysis of sliding and pressure distribution during a repositioning of persons in a simulator chair.

This study was undertaken to investigate the effect of system tilt and back recline angles on sliding and pressure distribution of seated subjects. Ten able-bodied subjects adopted successively 12 postures on a multiadjustable simulator chair. The system tilt angle was varied from 0 degrees to 45 degrees posterior tilt, while the seat to back angle varied from 90 degrees to 120 degrees. A maximum of 40.2% of weight shift was found when combining a system tilt angle of 45 degrees to a seat to back angle of 120 degrees. Maximum value of 74 mm of sliding was observed for the acromion marker during repositioning. Significant weight shift at the level of the seat is obtained only when the system tilt angle exceeds 15 degrees in a posterior direction. We can put forward here that a small tilt < or =15 degrees can be used to adjust back pressure distribution, whereas large posterior tilts are used for an effective weight shift at the seat level. The peak pressure gradient remains in general in the interval of +/-30% from the neutral posture for the able-bodied subjects and is fairly constant at 15 degrees of tilt. A significant amount of displacement along the back and seat reference plane were found for the shoulder and hip markers, but this displacement does not necessarily correspond to a pure translation motion of the pelvic segment.

Adult↗
PubMed2001

Kinematic modeling for the assessment of wheelchair user's stability.

A computer kinematic model was developed to simulate the lateral and transverse stabilities of wheelchair users in order to compare the effect of different backrests. This model is composed of ellipsoids and parallelepipeds representing the main components of the human body, the seating devices and the wheelchair. A fifteen-segment three-dimensional (3-D) model linked by spherical and revolute joints was created using the ADAMS software (Mechanical Dynamics, Inc.). Torsional springs and dampers are used at the joints to represent four sets of articulation stiffness. Seating devices are represented with 45 rectangular surface patches. The interface between human body and seating devices is modeled by contact elements, which included the specification of stiffness, damping, and deformation of cushions and buttocks. Simulations of a user and his wheelchair moving at 1.4 m/s on a tilted pathway were performed. Different indexes [trunk lateral tilt (TLT) and trunk transverse rotation (TTR)] were measured and compared to those of a similar experimental study on four subjects. The effect of joint stiffness was quantified and a sensitivity study showed the importance of the hip, neck, lumbar, and thoracic joint stiffness on model response (between 16% and 68%). Two backrests (standard and highly contoured) were tested with the kinematic model and their stability compared. Overall, the coherence between the simulations and the experiments shows that this approach is appropriate to compare various seating devices (maximal difference of 1.3 degrees between the simulated and experimental curves for the intermediate joint stiffness sets). The smallest rotations of the highly contoured backrest (6.3 degrees versus 8.9 degrees for TLT and 3.9 degrees versus 6.7 degrees for TTR) suggest that the contouring of the mid torso is more efficient than the lower torso to provide stability to the wheelchair user. This model is an adequate tool to test and improve the design of seating aids.

Biomechanical Phenomena↗
PubMed2000

Biomechanical analysis of legrest support of occupied wheelchairs: comparison between a conventional and a compensatory legrest.

This study was undertaken to investigate the effects of elevating legrest on posture and pressure distribution in a group of ten able-bodied subjects sitting in a manual wheelchair. Two types of legrest were tested: a conventional elevating legrest with a fixed axis of rotation, and a compensatory elevating legrest with a moving axis of rotation. A three-dimensional (3-D) kinematics analysis was carried out to assess body posture simultaneously with pressure measurement data collected at the back, seat, calf and foot supports. The compensatory legrest enables to lengthen foot support as the legrest proclines. This compensation at the knee joint level has a beneficial effect in minimizing pelvic and thigh motion as well as in reducing pressure distribution under seat and foot supports. In contrast, the use of a conventional legrest modifies significantly the subject's posture and induces a substantial increase of 40% on pressure data under ischial tuberosities in procline position. These findings are important for disabled and elderly people who need to elevate their lower leg frequently.

Adaptation, Physiological↗
PubMed2000

Determination of generic body-seat interface shapes by cluster analysis.

The purpose of this study was to determine typical or generic shape patterns of the buttock-seat interface for elderly wheelchair users. The group of subjects was composed of 30 elderly people (aged 65 or older) and the shapes of the body-seat interface were measured by the electronic shape sensor (ESS). By analyzing the dissimilarity in geometrical shape descriptors or parameters, four distinct generic shapes were identified by means of the cluster analysis method. The results suggest that the generic shapes were mainly characterized by the lateral symmetry of the shapes. The determination of elderly people's seat interface shapes into distinct clusters may lead to a more comprehensive understanding of the seat support interface and more effective seat cushion designs.

Aged↗
PubMed1999

Assessment of geometric and mechanical parameters in wheelchair seating: a variability study.

A measurement method has been developed to quantify the posture of able-bodied subjects seated in their wheelchair. Fourteen geometric parameters were measured in order to represent the pelvis, trunk and lower limbs orientations. They were defined by digitizing the three-dimensional (3-D) position of 23 anatomical landmarks using a mechanical articulated arm (Microscribe3D, Immersion Corporation). Mechanical parameters were used to measure the maximum pressure, mean pressure and peak pressure gradient on the seat and the back of the wheelchair using a force sensing array (Vista Medical, Inc.). A third set of parameters combining mechanical and geometric measurements were defined to represent pelvic tilt and ischial pressure orientations. However, different types of errors are associated to the measurement of these geometric and mechanical parameters. The purpose of this study was to evaluate these errors and their impact on the precision of the various parameters on a sample group of five able-bodied subjects. Results showed that variability of most of the geometric parameters is below 2 degrees with the sagittal rotation of the pelvis presenting the highest variability (3.8 degrees) and the thigh angle the lowest one (0.5 degrees). The variability of the mechanical parameters were respectively equal to 4.9% for the mean pressure, 9.3% for the peak pressure gradient and 16.9% for the maximum pressure under ischial tuberosities. It is suggested that the method proposed in this paper could be used as an accurate procedure to characterize the posture of subjects sitting in a wheelchair.

Adult↗
PubMed1996

Internal work estimation in three-dimensional gait analysis.

Many studies concerning the internal work of human motion have used two-dimensional kinematic models to estimate kinetic energy of the segments. The generalised co-ordinate concept has been applied here to a simultaneous and bilateral gait analysis. A three-dimensional kinematic model based on quaternions has been developed. To estimate the kinetic energy of a multi-body system, only two constants and two variables are needed: the segment body mass, the inertia tensor, the position and the orientation of the local co-ordinate system with respect to the inertial co-ordinate system. The variation of the kinetic energy is used in the calculation of the internal work for an able-bodies subject during the gait cycle. Both the internal work and the instantaneous energy correlation coefficient enable the determination of a conservative phase delimited by the beginning of the single support phase until the flat-foot phase, and a non-conservative phase corresponding to the period from heel-off to contralateral heel-strike including the double support phase.

Adult↗
PubMed1993

Comparison of gait between young adults fitted with the space foot and nondisabled persons.

Prosthetic feet having new keel configurations were specially designed to store deformation energy during early and midstance and release it at push-off. These prosthetic components display longitudinal symmetry favoring good energy storage/release capability in the sagittal plane. The need for inverters/everters either as independent components or within the foot structure has long been recognized. This article documents the walking and slow jogging performances of six young adults wearing below-knee prostheses fitted with the Space Foot, a flexible foot prosthesis that provides medio-lateral control at heel-strike and lateral and forward propulsion at push-off. Results indicate that the Space Foot behaves as a flexible keel foot prosthesis. Its gait performances are also good for fast walking; however, the Space Foot's actual design should be modified if used in sporting activities involving running.

Adult↗
PubMedDate not supplied

Evaluation of the new flexible contour backrest for wheelchairs.

A new flexible contour backrest for wheelchairs was designed with the objectives of offering adequate posture, uniform pressure distribution, and comfort to the users while keeping the advantages of conventional sling backrests, such as easy to fold, light weight, unobtrusive, and airy. The purpose of this study is to compare the new backrest with two commercially available wheelchair backrests, an adjustable-tension (AT) backrest and a back cushion on a rigid support (RS), in terms of pressure distribution, back profile accommodation, and short-term comfort. Evaluations were done with 15 nonimpaired subjects in a static position. It was shown that the new backrest distributes pressure in a more uniform way than the AT and in a way similar to the RS, while giving a better fit to subjects' trunks than other backrests because of its multiple adjustments. Finally, subjects felt that the new backrest is as comfortable as the RS and more comfortable than the AT.

Adult↗