Backrest Position Research Articles

An analysis of three dimensional changes to comprehensively evaluate the occlusion time, disclusion time, point of first contact and force distribution at various head positions using Tekscan III: An in vivo study

Aim: This study aims to evaluate the changes in occlusal contacts resulting from variations in head postures (supine[S], semi-supine [SS], upright with head rest support [HR], and without head rest support [WHR]) after occlusal adjustment of conventional fixed dental prostheses using Tekscan III. Settings and Design: A cross-sectional study on 15 patients with missing single molars and undergone replacement with a fixed dental prosthesis. Materials and Methods: Fifteen patients with a three-unit tooth-supported fixed dental prosthesis replacing a missing single posterior tooth were included. Tekscan III was used to analyze occlusion time (OT), disclusion time (DT), initial tooth contact, and relative bite force in different head postures by adjusting the backrest position before and after equilibration. Occlusal adjustments were performed to achieve the balance between the right and left halves. Statistical Analysis Used: The data were statistically analyzed using ANOVA and paired t-test. Results: Posterior shift of initial tooth contact was observed from SS to supine and upright positions, whereas an anterior shift occurred from SS to WHR support posture. High-intensity forces were observed before the occlusal adjustment in various head positions, and these forces changed after adjustments in SS position. However, medium-intensity force occlusal prematurities persisted in other head postures even after corrections in SS position. There was a significant difference in OT but not in DT in all head postures after equilibration. When OT was compared from SS to remaining posture after equilibration, the major difference was found from SS to head rest (HR) and supine to HR posture which infers the need for selective grinding in these postures. Conclusion: Considering the various changes while changing the head position from the SS position to the other functional position, it can be inferred that there is a need to consider recalibration of occlusal contacts in all the functional postures.

Study on the influence of seating orientation during frontal impacts by child occupant human body model response analysis

Objective Autonomous driving cars must be developed to ensure that children will have the highest level of protection in case of collision. Changes to the vehicle cabin design (different seat orientations, fully reclining seats, etc.) may significantly impact child occupant safety. Understanding child occupant responses under these new conditions is necessary to decrease risk and enhance child safety. In this study, child occupant response in different seating orientations exposed to frontal impacts with a focus on the head injuries and kinematics was analyzed. Methods Finite elements simulations were performed using the PIPER 6-year-old human body model (HBM). All simulations were carried out in a generic full vehicle environment. The child model was positioned in an adequate generic car restraint system (CRS) in the left rear vehicle seat in 4 seating orientations: 0° (forward-facing position), 30°, 60°, and 90° (living room position). Two scenarios were evaluated for all seating orientations according to the left front seat backrest position: reclined position nominal upright and rest position (55°). All seat configurations were subjected to the mobile progressive deformable barrier frontal impact (European New Car Assessment Programme [Euro NCAP] frontal impact testing protocol). A total of 8 scenarios were simulated in LS-DYNA. Results Based on the Euro NCAP injury risk rate, 90° seating orientation (living room position) was the safest among all selected scenarios independent of the left front seat backrest position. The worst case was found in 60° seat rotation. The highest values for Head Injury Criterion (HIC) and head acceleration (Acc 3 ms) were noted for this case. Higher Brain Injury Criterion (BrIC) values were observed at higher seat rotation angles. Hence, a 90° seating orientation showed the highest BrIC value. Attending to the skull stress, greater head injuries were caused principally by contact with the vehicle interior (seat headrest). Maximum stress values were reached at 30° and 60° seating orientations with the front seat in rest position. In 90° seating orientation, high stress values were also identified. Conclusions These results show that attending to these new seating orientations, current child safety standards are not sufficient to ensure children the highest level of protection. Other additional criteria such as BrIC or skull stress that offer a way to capture brain injuries should be used.

A model-based approach for the analysis of aircraft seating comfort.

Aircraft seating comfort has a significant impact on passenger on-board experience. Its assessment requires the adoption of well-designed strategies for data collection as well as appropriate data analysis methods in order to obtain accurate and reliable results. This paper focuses on the assessment of aircraft seating comfort based on subjective comfort responses collected during laboratory experiments and taking into account seat features and passenger characteristics. The subjective comfort evaluations have been analyzed using a model-based approach to investigate the relationship between overall seating comfort and specific seat/user characteristics. The results show that the overall seating comfort perception is significantly influenced by the thickness of the seat pan, the backrest position (upright or reclined), the age of the passenger and the passenger perception of being comfortably supported at the lumbar region. The adopted model-based approach allows the analysis of subjective seating comfort data taking into account their ordinal nature as well as the dependency between evaluations provided by the same subject.

Influence of backrest angle on swallowing musculature activity and physical strain during the head lift exercise in elderly women compared with young women.

The head lift exercise (HLE) is the most common exercise for strengthening the swallowing musculature in clinical situations. This study investigated whether a change in the backrest angle of a bed influences swallowing musculature activity and physical strain during the HLE and whether it can generate an appropriate exercise load for swallowing musculature activity for older women compared with younger women. Participants were 10 elderly women and 10 young women, each of whom performed the HLE with a backrest randomly angled at 0°, 15°, 30° and 45°. The activity of the suprahyoid, infrahyoid and sternocleidomastoid muscles was assessed with electromyography. The perception of fatigue was measured with the Borg Rating of Perceived Exertion Scale. The activity of the infrahyoid and sternocleidomastoid muscles in elderly women was significantly lower when the angle of the backrest was raised to 45° vs 0°. In both groups, the Borg rating decreased significantly at the 30° and 45° backrest positions vs the 0° and 15° positions. The activity required for the suprahyoid and infrahyoid muscles in elderly women at a 30° backrest position was almost equal to the activity required by these muscles in young women at a 0° backrest position. In elderly women, it is possible that the HLE with the backrest at a 30° angle may be easier and provide a more appropriate exercise load for strengthening the swallowing muscles.

End user evaluation of a Kneeling Wheelchair with “on the fly” adjustable seating functions

A “kneeling” ultralight wheelchair prototype has been developed that allows users to adjust seat position “on the fly” for different activities throughout the day. The wheelchair includes independent adjustment functions for rear seat height, front seat height (“kneeling”) and backrest angle. Aim: This work aimed to gather feedback about the wheelchair’s functionality and performance through end user evaluation trials. Methods: Eight manual wheelchair users evaluated the prototype Kneeling Wheelchair for a range of activities. User perspectives on parameters such as usability, comfort, stability and effectiveness were obtained through both open-ended and Likert-scale rating questions. Results: Results indicate several potential benefits of the adjustment functions of the Kneeling Wheelchair. Rear seat height adjustment may facilitate a number of activities of daily living, as well as provide benefits for comfort and social interactions. Back rest adjustment may increase comfort and stability on slopes. Front seat height adjustment may be beneficial for transfers and conducting sustained low-to-the-ground activities. While benefits of this adjustment function were described by many participants, some struggled with usability of the kneeling mechanism and rated this function less favourably than the other two. Conclusion: The findings of this study will inform future iterations of the Kneeling Wheelchair design and may spur future developments in wheeled mobility. In the long-term, it is anticipated that novel wheelchair solutions, such as the one described in this paper, may support improved health, quality of life and community participation for people with mobility impairments.Implications for rehabilitationWheelchairs that allow users to easily adjust seat and backrest position “on the fly” to better suit different tasks throughout the day may provide benefits such as facilitating activities of daily living.A front seat height adjustment feature on a new wheelchair prototype may be beneficial for transfers and conducting sustained low-to-the ground activities.End user evaluations can provide valuable insight to direct future design modifications and innovation.

The Effect of Backrest Roller on Warp Tension in Modern Loom

The Backrest roller is one of the key parts of the weaving machine. In this study, the effect of the various position of backrest and dropper has been assessed. The tension is measured by using the integrated tension measuring device of the loom. The tension can be found on the display board. The effect of backrest position can be described in two different ways viz. keeping constant dropper position (distance between dropper line and backrest roller) and keeping constant dropper depth (distance between held frame and dropper line). If dropper position (distance between backrest roller to dropper line) is kept constant then the backward movement of backrest roller will entail low tension. The reason behind this is, the dropper weight will be moved toward the backrest roller and will lose its influence on warp tension. But if dropper depth is kept constant (i,e dropper line is kept intact) then the backward movement of backrest will require more tension as the influence of dropper will more on warp length. On the other hand, when backrest height is lowered then, the downward movement of backrest roller will need low tension and upward movement of backrest roller will need more tension. As the warp length and lap angle increases with the backrest height. In this paper, the whole phenomenon is explained with illustration.

Influence of dental chair backrest inclination on the registration of the mandibular position

Statement of problemVarying the inclination of the dental chair backrest might alter the distribution of occlusal contact points. PurposeThe purpose of this study was to identify the influence of backrest inclination on the registration of the mandibular position. Material and methodsTen participants aged between 18 and 30 years with a complete permanent dentition, uncompromised motor function, no tooth mobility, and no temporomandibular disorders were selected. To register interocclusal contacts, an autopolymerizing methylmethacrylate device was adapted to the maxillary anterior teeth and a composite resin increment was added to the mandibular central incisors. Contacts were registered with the following variations in the inclination of the dental chair backrest: 90 degrees, 120 degrees, and 180 degrees. A standardized digital photograph was made of each mark in each backrest position, and the images were superimposed to measure the distances in registration from 90 to 120 and from 90 to 180 degrees. Data were analyzed with the Student paired t test (α=.05). ResultsWhen the chair was inclined from the 90-degree to the 120-degree position, the mandible was repositioned posteriorly by a mean of 0.67 mm, but the difference was not statistically significant. When the chair was inclined from the 90-degree to the 180-degree position, however, the mandible was repositioned posteriorly by a statistically significant mean of 1.41 mm. ConclusionsMandibular position is influenced by increasing inclination, and this influence was statistically significant at a 180-degree incline.

Influence of Different Seating and Crank Positions on Muscular Activity in Elite Handcycling - A Case Study

Due to rising public focus scientific analysis of performance parameters is getting more and more important in paralympic sports. Several studies have been performed to investigate different design parameters of handcycles (e.g. crank length) already; however, most of those were done with able-bodied subjects, widely unfamiliar to handcycling. In this study bilateral surface electromyography (sEMG) of several muscles of the upper body and arms of an elite handcyclist (multiple medal-winner in Paralympic Games and World Championships) is performed with different crank lengths, crank positions and backrest positions at power levels of 130, 160 and 190W resulting in a total of 22 measurements. sEMG data were recorded bilaterally at a recording frequency of 1000Hz using Ag/AgCl electrodes. Concurrently the crank position was acquired with ten Vicon Bonita infrared cameras recording at 100Hz. EMG data were rectified, smoothed and normalized to crank-cycle duration (0-360 deg) for each single crank-cycle. Phases of activity for each muscle (i.e. EMG amplitude exceeds 30% of maximum amplitude) and integrated EMG (iEMG) as an indicator for net muscular e ort were calculated. Results showed that amplitude and iEMG were higher for higher power output and shorter cranks, crank and backrest position influenced several muscles but results were always similar for similar shoulder-crank-distances. It could be shown, that muscular effort is clearly influenced by the handcycle parameters investigated and that these measurements can be used to individually optimize the position in a handcycle with regard to muscular effort.

Influence of posture on the ventilatory pattern and the thoraco-abdominal kinematics of patients with chronic obstructive pulmonary disease (COPD)

Objective: Evaluate the influence of posture on ventilatory pattern, compartmental distribution of volume of chest wall and thoraco-abdominal kinematics of patients with severe chronic obstructive pulmonary disease (COPD). Design: Cross-sectional study. Methods: Twelve, male patients with severe COPD (Forced Expiratory Volume in the first second (FEV1) = 24.35 ± 4.52%, Forced Vital Capacity% (FVC%) = 60 ± 13.39% and relationship FEV1/FVC = 53.42 ± 14.47). The distribution of the volume of the ribcage [pulmonary rib cage (Rcp), abdominal ribcage (Rca) and abdomen (Ab)] during quiet breathing in a sitting position without back support (SWB), sitting with backrest (SB) and supine position (SUP) was determined using an opto-electronic plethysmograph. Results: The following differences were observed: a greater tidal volume in the SWB position when compared to the SB position (p = 0.01); greater expiratory time in the SUP position in relation to the SWB (p = 0.03) and SB (p = 0.01); and increased abdominal contribution to the tidal volume in the SUP position in relation to the SWB (p < 0.01) and SB (p < 0.001). No difference was found in the thoraco-abdominal synchrony among the positions. Conclusion: Sitting position without back support enhances the activation of respiratory muscles by increasing the tidal volume and supine position seems to favor lung deflation by increasing the expiratory time. It seems appropriate to adopt these positions to optimize the ventilation/perfusion relationship and physiotherapeutic intervention in different clinical conditions.

The effect of weaving machine setting on fabric skewness

The effect of air-jet loom settings, such as initial warp tension, back rest position, shed closing time and shed height, on fabric skewness has been investigated. Skewness was related with loom setting parameters during commercial weaving machine trials. Adjustment of loom settings was carried out at different levels without changing the properties of warp and weft yarns and fabric construction. It has been found that initial warp tension and shed height are the most significant factors affecting on fabric skewness. Skewness is decreased with an increase of the initial warp tension, especially when the shed height is 26°, but this effect is non-linear; when adjusting the shed height from 22° to 26°, fabric skewness is increased. Adjustment of the shed closing time from normal to late decreased fabric skewness, whilst raising the backrest roller over zero position did not have a significant effect on fabric skewness.

Taguchi analysis of fabric shrinkage

This article reports on the effects of fabric constructional factors such as fabric sett, warp tension, back rest position, and pick insertion rate, on the warp-way and weft-way shrinkages of a three-up-one-down twill woven fabric using a Taguchi design of experiments. It was observed that the fabric shrinkage in the warp direction was mostly affected by the change in the number of picks per inch, followed by warp tension, number of ends per inch, number of picks per minute, and back rest position, respectively. The fabric shrinkage in the weft direction was found to be mostly affected by the change in number of ends per inch, followed by number of picks per inch, back rest position, number of picks per minute, respectively and least affected by warp tension. It was observed that the aforesaid five factors were able to explain 99.02 % and 82.81 % of the total variation of fabric shrinkage in the warp and weft directions, respectively.

The effect of crank position and backrest inclination on shoulder load and mechanical efficiency during handcycling

Handbikes come in different models and setups, but only limited knowledge is available on the handbike-user interface. The aim of this study was to identify optimal handbike setups, assuming that in such a setup mechanical efficiency is high, while shoulder load is low. Thirteen subjects with a spinal cord injury (paraplegia) performed handcycling with different handbike setups at constant power output: four crank positions (two distances, two heights) and four backrest inclinations. The O2-consumption, kinetics, and kinematics were measured to calculate mechanical efficiency and shoulder load (glenohumeral contact force, net shoulder moments, and rotator cuff force). The analysis showed that more upright backrest positions resulted in lower shoulder load compared with the most reclined position [glenohumeral contact force (260 vs 335 N), supraspinatus (14.4% vs 18.2%), and infraspinatus force (5.4% vs 9.8%)], while there was no difference in efficiency. Except for a reduction in subscapularis force at the distant position, no differences in shoulder load or efficiency were found between crank positions. Recreational handbike users, who want to improve their physical capacity in a shoulder-friendly way, should set up their handbike with a more upright backrest position and a distant crank placement.

Changes in Head and Neck Posture Using an Office Chair With and Without Lumbar Roll Support

A repeated measures observational study. To investigate change in sagittal alignment of head and neck posture in response to adjustments of an office chair with and without a lumbar roll in situ. Forward head posture has been identified as a risk factor for neck pain, and there is evidence to show that ergonomic correction in sitting may reduce the incidence of pain. The effect placement of a lumbar roll has on cervical spine posture has not been previously investigated experimentally but rather, is assumed to have a positive influence on head and neck posture. Thirty healthy male participants (18-30 years) were photographed while registered in the natural head resting position in each of 4 sitting positions with and without a lumbar roll in situ. Two positions incorporated adjustments to the back rest and 1 to the seat pan of the office chair. The craniovertebral (CV) angle, as a determinant of head and neck posture was measured from the set of digitized photographs obtained for each participant. Comparisons between the CV angle in all postural registrations were made using a mixed model analysis adjusted for multiple comparisons. Of the positions examined, significant differences in the mean CV angles were found with the backrest of the chair at 100 degrees and at 110 degrees (P < 0.001). With the lumbar roll in situ and the backrest position at 110 degrees , there was a significant increase in the mean CV compared with the angle without the lumbar roll in situ (2.32 degrees , 95% confidence interval: 1.31-3.33; P < 0.001). The degree of angulation of the backrest support of an office chair plus the addition of lumbar roll support are the 2 most important factors to be taken into account when considering seating factors likely to favorably change head and neck postural alignment, at least in asymptomatic subjects.

Effects of backrest positioning and gear ratio on nondisabled subjects' handcycling sprinting performance and kinematics

Backrest position is a significant parameter in handcycling that one must consider when seeking to optimize the user-to-chair interface. We studied the effects of backrest position on handcycle propulsion kinematics. Ten nondisabled partici pants with no handcycle propulsion experience repeated an 8 s sprint with three backrest positions (backrest angle between 45 degrees and 50 degrees to the horizontal, backrest angle between 65 degrees and 70 degrees to the horizontal, and without backrest) and three gear ratios (GRs) (GR22/21 = low, GR32/21 = medium, and GR44/21 = high). We used three-dimensional movement analysis to calculate the average maximal velocity, cycle frequency, and angle parameters for the arms and trunk. Our results showed statistically higher trunk flexion/extension (p < 0.001) and maximal velocity (p < 0.001) when a backrest was not used. Moreover, these differences were accentuated as the GR increased (GR44/21). Our results suggest that handcycle users with unimpaired upper-body and trunk function can improve handcycling performance by removing the backrest. Nevertheless, future studies on specific groups of subjects with spinal cord injury should be conducted.

Investigation of the transmission of fore and aft vibration through the human body

Understanding the behavior of human body under the influence of vibration is of great importance for the optimal motor vehicle system design. Therefore, great efforts are being done in order to discover as many information about the influence of vibration on human body as possible. So far the references show that the major scientific attention has been paid to vertical vibration, although intensive research has been performed lately on the other sorts of excitation. In this paper, the results of the investigation of behavior of human body, in seated position, under the influence of random fore and aft vibration are shown. The investigation is performed by the use of an electro-hydraulic simulator, on a group of 30 healthy male occupants. Experiments are performed in order to give results to improve human body modeling in driving conditions. Excitation amplitudes (1.75 and 2.25 m/s(2) rms) and seat backrest conditions (with and without inclination) were varied. Data results are analyzed by partial coherence and transfer functions. Analyses have been performed and results are given in detail. The results obtained have shown that the human body under the influence of random excitations behaves as a non-linear system and its response depends on spatial position. Obtained results give necessary data to define structure and parameters of human biodynamic model with respect to different excitation and seat backrest position.

Effects of Backrest Position on Central Venous Pressure and Intracranial Pressure in Brain Surgery Patients

This study was done to investigate the effects of backrest elevation of 0 degree and 30 degrees that minimize the risk of increasing ICP when CVP is measured. Subjects were sixty-four patients who stayed in the neurosurgical intensive care unit after brain surgery at two university-based hospitals. CVP, blood pressure, heart rate and ICP were measured along with position changes in order of backrest position with primary 30 degrees backrest position, 0 degree backrest position and secondary 30 degrees backrest position. For data analysis, one-group, repeated-measures analysis of variance design was used in SAS program. Backrest elevations from 0 degree to 30 degrees did not alter the CVP without increasing the ICP. Therefore, 30 degrees backrest position is a preventive position without increasing ICP. 30 degrees backrest position might be appropriate for brain injury patients when CVP is measured.

Effect of Backrest Elevation on the Development of Ventilator-Associated Pneumonia

Ventilator-associated pneumonia is a common complication of mechanical ventilation. Backrest position and time spent supine are critical risk factors for aspiration, increasing the risk for pneumonia. Empirical evidence of the effect of backrest positions on the incidence of ventilator-associated pneumonia, especially during mechanical ventilation over time, is limited. To describe the relationship between backrest elevation and development of ventilator-associated pneumonia. A nonexperimental, longitudinal, descriptive design was used. The Clinical Pulmonary Infection Score was used to determine ventilator-associated pneumonia. Backrest elevation was measured continuously with a transducer system. Data were obtained from laboratory results and medical records from the start of mechanical ventilation up to 7 days. Sixty-six subjects were monitored (276 patient days). Mean backrest elevation for the entire study period was 21.7 degrees . Backrest elevations were less than 30 degrees 72% of the time and less than 10 degrees 39% of the time. The mean Clinical Pulmonary Infection Score increased but not significantly, and backrest elevation had no direct effect on mean scores. A model for predicting the Clinical Pulmonary Infection Score at day 4 included baseline score, percentage of time spent at less than 30 degrees on study day 1, and score on the Acute Physiology and Chronic Health Evaluation II, explaining 81% of the variability (F=7.31, P=.003). Subjects spent the majority of the time at backrest elevations less than 30 degrees . Only the combination of early, low backrest elevation and severity of illness affected the incidence of ventilator-associated pneumonia.

Effect of Backrest Position on Intracranial Pressure and Cerebral Perfusion Pressure in Individuals with Brain Injury

Head elevation is a conventional nursing procedure for brain-injured individuals with intracranial hypertension; it is performed with the intent of reducing intracranial pressure (ICP) by means of a noninvasive physical intervention. However, in certain circumstances, head elevation puts the brain-injured individual at risk for secondary cerebral injury because of impaired arterial blood pressure and compromised cerebral perfusion pressure (CPP). A systematic literature search was conducted to evaluate existing evidence regarding the effect of changing the backrest position on ICP and CPP in brain-injured individuals. Eleven articles were retrieved. In nine articles it was concluded that ICP significantly decreased at 30 degrees of head elevation compared with a flat position. Five of the nine articles showed no statistical significance in the magnitude of change in CPP from a flat position to 30 degrees of head elevation. Major limitations in the 11 articles were small sample sizes and unclear study protocols, which may have caused a failure to detect the effect of head elevation. In clinical practice, intensive care unit staff members need to cautiously perform head elevation with a thorough understanding of its physiologic effect and potential hazard. Future research should investigate the effects of therapeutic positions on different neurological and neurosurgical populations and explore the combination of head elevation and lateral side-lying positions.

Predictors of backrest elevation in critical care.

Low backrest and supine positions are associated with increased mortality and ventilator associated pneumonia (VAP). Data are not available across ICU settings about the level of backrest position used and its relationship to enteral feeding and hemodynamic status. The purpose of this descriptive study was to document the level of backrest elevation and position and identify factors associated with and predict positioning in a medical, surgical and neuroscience intensive care unit. Data were collected randomly in each unit over a 6-week period, resulting in 506 observations for170 patients. Backrest elevation was determined by electronic bed read-out or bed frame elevation gauge. BP, HR and enteral feeding status were retrieved from the medical record. Results showed that mean backrest elevation was 19.2 degrees and 70% of subjects were supine. No difference in backrest elevation among units was found. Significant correlations between backrest elevation and systolic BP (r=0.15, P=0.006); and backrest and diastolic BP (r=0.13, P=0.02) were found. There was no difference in backrest elevation between patients being fed and not being fed. Differences in backrest elevation for intubated versus nonintubated patients approached significance (P=0.07) with intubated patients at lower backrest elevations. In summary, use of higher backrest elevations (>30 degrees ) is minimal, is not related to feeding and minimally related to hemodynamic status. Strategies to meet published recommendations for backrest elevation (30-45 degrees ) must include repeated feedback about nurse's use of backrest elevation and estimates of elevation.

Effect size: utility and application in neuroscience nursing.

Effect size is used in single studies to complement inferential statistical analysis. It also is used to compare and synthesize data across studies in meta-analysis. Effect size provides information about clinical importance of differences found in research observations. For researchers, effect size is useful in establishing support for the theoretical framework of a story and in planning for future research. Application of effect size to data in three studies about the effects of backrest position on ICP and CPP in brain-injured adults illustrates the utility of effect size analysis in neuroscience nursing research.