Strap Tension Research Articles

Evaluating the effective pressure applied by a valgus knee orthosis in individuals with medial knee osteoarthritis based on the dose–response relationship

BackgroundThere is evidence that valgus knee orthosis improves clinical and biomechanical outcomes in individuals with medial knee osteoarthritis (MKOA). It is unclear whether variations in pressure application by orthosis straps can affect the biomechanical outcomes. This study aimed to determine the dose–response relationship between different orthosis straps tensions and changes in knee adduction moment (KAM) parameters in individuals with MKOA. MethodTwenty-four individuals with symptomatic MKOA were enrolled in this quasi-experimental study. Five tension conditions in orthosis straps were tested in 20-mmHg increments, from 0 (no pressure) to 100 (maximal pressure) mmHg. Patients were asked to adjust the orthosis strap tension based on their perceived comfort. After each condition, a 3D gait analysis was performed, and KAM parameters were calculated. The participants also reported their satisfaction with knee orthosis adjustment for each pressure condition. ResultsWith successive increases in strap tension from 40 to 80 mmHg, the first peak, second peak, and angular impulse of KAM decreased nonlinearly (from 6 % to 25 %). Increasing the orthosis strap tension to 100 mmHg significantly decreased (P < 0.05) the participants’ satisfaction level. The effective dosages (IC50) of pressure for the first peak, second peak, and angular impulse of KAM as responses were 58, 65, and 69 mmHg, respectively. ConclusionThe KAM decline was not linear as the strap pressure increased. Patients were dissatisfied with orthosis adjustment when strap tension was above 80 mmHg. The optimum dosage of pressure on the knee joint's lateral side for adjusting an orthosis' strap tension is approximately 69 mmHg.

Reducing Mask-Related Pressure Injuries in Pediatric Patients During Noninvasive Ventilation by Targeting Patient Mask Leak: A Quality Improvement Initiative.

To compare outcomes following implementation of patient mask leak range of 25 to 55 liters per minute (lpm) to guide strap tension of sleep masks during noninvasive ventilation against baseline data with no patient mask leak range on number of noninvasive mask-related pressure injuries (PIs). All noninvasively ventilated pediatric acute care patients admitted to general wards and intensive care units between February 1, 2018, and February 1, 2019, in a quaternary hospital in the southwest United States. Using the Plan Do Study Act model, we employed an intervention to examine the rate of PIs per noninvasive positive pressure ventilation (NIPPV) days and patient-days before and after implementation of patient mask leak parameters between 25 and 55 lpm to guide mask strap tension. Since patients are at an increased risk of sleep mask-related PIs only when on NIPPV, we sought to describe that as number or PIs per number of days at risk, described as NIPPV days, and patient days which is the traditional denominator for wounds and hospital-acquired conditions. Preintervention, 6 out of 115 subjects (5.2 %) incurred PI at a rate of 0.51 per 100 NIPPV days or 0.26 per 1000 patient-days. Of the 1932 NIPPV days since education was completed, only 1 subject out of 87 (1.1%) incurred a high-stage PI (0.05/100 NIPPV days-a 96.79% reduction or 0.05/1000 patient-days-a 92.86% reduction). Upon reaching more than 90% compliance with patient mask leak range in December 2018, 1221 NIPPV days resulted in 0 noninvasive mask-related PIs. Greater than 90% compliance with a patient mask leak of 25 to 55 lpm allowed us to successfully achieve our hospital's operating plan goal of 0.15 of 1000 patient-days within this group. Maintaining a patient mask leak range between 25 and 55 lpm should be considered as part of proper fit for pediatric patients using NIPPV with a mask. Additional work is needed to assess this leak range in more children and in studies conducted at multiple sites.

ストラップ張力の微調整機構によるNPPVマスクフィッティングの安定化

ストラップ張力の微調整機構によるNPPVマスクフィッティングの安定化

The effects of the tension of figure-8 straps of a soft ankle orthosis on the ankle joint kinematics while walking in healthy young adults: A pilot study

BackgroundFigure-8 straps are commonly used in ankle orthoses, which are provided to reduce the risks of primary and recurrent sprain by providing functional support. Functional treatment with ankle orthoses can provide better rehabilitation than immobilization for a mild ankle sprain. However, it is not known how much tension should be applied to the straps while donning the orthosis to optimize its effectiveness. Research questionThe aim of this study was to investigate the effects of figure-8 strap tension of a soft ankle orthosis on ankle joint kinematics in the sagittal, coronal, and transverse planes during gait in healthy young adults. MethodsTen healthy adults (five males and five females) were enrolled in this study. The 3-dimensional motion analysis system was used to evaluate the ankle kinematics of the participants during gait under five conditions: no soft ankle orthosis, soft ankle orthosis with no figure-8 straps tension (lace-up only), 50 N, 80 N, and 110 N tension of the figure-8 straps, respectively. All participants walked in a straight path at a comfortable speed. ResultsPlantarflexion angles were significantly reduced with 110 N of tension in the figure-8 straps when compared to the lace-up only and a moderate correlation with r = 0.34 (p = 0.03) was observed between the tensions of figure-8 straps and maximum plantarflexion angles at pre-swing of a gait cycle. No significant effects on ankle joint angles were demonstrated in the coronal and transverse planes. SignificanceThis study showed that increasing the tension of the figure-8 straps could restrict the ankle joint plantarflexion angle during pre-swing in gait. However, it might not affect inversion/eversion or internal/external rotation angles of the ankle joint in individuals without ankle pathologies.

Workflow to develop 3D designed personalized neonatal CPAP masks using iPhone structured light facial scanning

BackgroundContinuous positive airway pressure (CPAP) is a common mode of respiratory support used in neonatal intensive care units. In preterm infants, nasal CPAP (nCPAP) therapy is often delivered via soft, biocompatible nasal mask suitable for long-term direct skin contact and held firmly against the face. Limited sizes of nCPAP mask contribute to mal-fitting related complications and adverse outcomes in this fragile population. We hypothesized that custom-fit nCPAP masks will improve the fit with less skin pressure and strap tension improving efficacy and reducing complications associated with nCPAP therapy in neonates.MethodsAfter IRB approval and informed consent, we evaluated several methods to develop 3D facial models to test custom 3D nCPAP masks. These methods included camera-based photogrammetry, laser scanning and structured light scanning using a Bellus3D Face Camera Pro and iPhone X running either Bellus3D FaceApp for iPhone, or Heges application. This data was used to provide accurate 3D neonatal facial models. Using CAD software nCPAP inserts were designed to be placed between proprietary nCPAP mask and the model infant’s face. The resulted 3D designed nCPAP mask was form fitted to the model face. Subsequently, nCPAP masks were connected to a ventilator to provide CPAP and calibrated pressure sensors and co-linear tension sensors were placed to measures skin pressure and nCPAP mask strap tension.ResultsPhotogrammetry and laser scanning were not suited to the neonatal face. However, structured light scanning techniques produced accurate 3D neonatal facial models. Individualized nCPAP mask inserts manufactured using 3D printed molds and silicon injection were effective at decreasing surface pressure and mask strap pressure in some cases by more than 50% compared to CPAP masks without inserts.ConclusionsWe found that readily available structured light scanning devices such as the iPhone X are a low cost, safe, rapid, and accurate tool to develop accurate models of preterm infant facial topography. Structured light scanning developed 3D nCPAP inserts applied to commercially available CPAP masks significantly reduced skin pressure and strap tension at clinically relevant CPAP pressures when utilized on model neonatal faces. This workflow maybe useful at producing individualized nCPAP masks for neonates reducing complications due to misfit.

Effect of UV-C germicidal irradiation (UVGI) on the structural integrity of N95 and KN95 respirators

This study focuses on reprocessing a group of filtering facepiece respirators (FFR) using ultraviolet germicidal irradiation (UVGI). The aim is to explore the possibility of disinfecting selected KN95 FFRs, in comparison with the N95 FFRs, and assess their viability for reusage. For this purpose, five models of unused N95 and KN95 FFR models obtained from the hospital were exposed to UV-C light using a customized UVGI chamber. The material integrity of treated FFRs was examined in terms of particle penetration and strap tension. The surface morphology of all models is inspected to determine the visible changes of each FFR upon exposure to 1–100 cycles (1 cycle is equivalent to 1 J/cm2 UV dose). The penetration test results indicate that the physical properties of the KN95 and N95 FFRs remain within permissible limits despite being reprocessed by up to 100 cycles (100 J/cm2). Using a microscope, the physical observations also reveal that no visible damage can be seen even after 100 J/cm2 exposure. Apart from the filter bodies, the tension of each strap was also found to not be significantly affected by UV radiation by at least 10 disinfection cycles (10 J/cm2). This confirms that KN95, as well as N95 FFRs, can be subjected to UV treatment as a means of disinfection.

Combat helmet liner design for blunt impact absorption using multi-output Gaussian process surrogates

A finite element based computational model simulating the standard drop tower test for military helmets was created and used in conjunction with a multi-output Gaussian process surrogate to seek different designs of helmets for improved blunt impact performance. Experimental drop test results were used for the validation of the model’s ability to simulate impact. The influence of foam stiffness, impact velocity, strap tension, as well as pad placement and size on parameters on the peak linear acceleration (PLA) of the headform was investigated for the first time through a surrogate model trained by strategically choosing simulation points. Impact velocity was found to have the greatest effect. The strap tension and foam pad stiffness ranges examined within this sampling plan were found to have less of an effect on the performance of the helmet than the pad size and shape parameters examined. The surrogate modeling approach was used to quantify the influence of design parameters and can lead to not only improved helmet designs but also new data-driven design metrics and testing standards to accelerate the development of TBI-mitigating helmets.

3D printed mask extenders as a supplement to isolation masks to relieve posterior auricular discomfort: an innovative 3D printing response to the COVID-19 pandemic

PurposeMany commonly used mask designs are secured by elastic straps looping around the posterior auricular region. This constant pressure and friction against the skin may contribute to increased wearer pain, irritation, and discomfort. The purpose of this work is to report a modified 3D printed mask extender to alleviate discomfort and increase mask wearability by relieving posterior auricular pressure from isolation masks.MethodsOur institutional review board designated this project as non-human research and exempt. As part of resourcing 3D printing laboratories along with individual 3D printers to provide resources to healthcare workers, mask extenders were printed to relieve posterior auricular pressure from individuals wearing isolation masks. The authors modifed an existing mask extender, increasing its length with accompanying peripheral rungs for isolation mask securement. 3D printing was performed with Ultimaker S5 (Ultimaker B.V.; Geldermalsen, Netherlands) and CR-10 (Creality3D; Shenzhen, China) 3D printers using polylactic acid filaments. The author’s modified extended mask extenders were printed and freely delivered to healthcare workers (physicians, nurses, technologists, and other personnel) at the authors’ institution.ResultsThe final mask extender design was printed with the two 3D printers with a maximum 7 straps printed simultaneously on each 3D printer. Mean print times ranges from 105 min for the Ultimaker S5 printer and 150 min for the CR-10. Four hundred seventy-five mask extenders were delivered to healthcare workers at the authors’ institution, with the demand far exceeding the available supply.ConclusionWe offer a modification of a 3D printed mask extender design that decreases discomfort and increases the wearability of isolation mask designs with ear loops thought to relieve posterior auricular skin pressure and ability to control strap tension. The design is simple, produced with inexpensive material (polylactic acid), and have been well-received by healthcare providers at our institution.

Analysis of the interface pressure exerted by the Chêneau brace in patients with double-curve adolescent idiopathic scoliosis.

The Chêneau brace has proven its effectiveness in treating the adolescent idiopathic scoliosis patients. However, no studies reported on the analysis of interface pressure in double-curve adolescent idiopathic scoliosis patients. In this study, we evaluated the interface pressure of the Chêneau brace action in double-curve adolescent idiopathic scoliosis patient treatment. A total of 72 (60 girls and 12 boys) patients aged 10 years and above participated in the study. The F-Socket transducers (9811E) were used to evaluate the pressure on the right thoracic and left thoracolumbar curves between normal and maximum strap tension and variation in these interface pressures with other tasks. Each patient was asked to do nine different tasks corresponding to daily activities, and the interface pressures for each activity were recorded for both normal and maximum tension. The resultant mean peak pressure in double-curve adolescent idiopathic scoliosis was higher for right thoracic curves than left thoracolumbar curves in all tasks. The pressure significantly increased at the task of maximal inspiration (p < 0.0001) for both types of curves for normal and maximum tension. The degrees of correction for the thoracic and thoracolumbar curves were 23.2% and 34.5%, respectively, after 6 months of brace use (23 h per day). Hence, we could not find any substantial correlation between mean peak pressure in the standing position and degree of scoliosis correction for two curves having r = 0.158, p = 0.356 and r = -0.024, p = 0.889 values.

Epoxy Resin Systems for Rapid Repair of Steel Members with Carbon Fibre

The repair of steel members with carbon fibre has applications in a broad variety of disciplines. Experimental work in the literature has typically identified high strength epoxy resins to bond the carbon fibre to the steel surface, with requirements of up to two weeks curing at ambient temperature, as recommended by the epoxy manufacturer. However, there may be applications in which repair in the field would require more rapid curing, so as to minimize disruptions to the service of the member or structure. This study presents an experimental program assessing four different epoxy resins for their strength and cure time. Double strap tension tests were undertaken, and the results indicated that certain epoxy resins reached full strength much more rapidly than others, while their strengths varied notably. Recommendations are made with respect to rapid strength repair of steel members with carbon fibre.

Investigating the effects of cervical collar design and fit on the biomechanical and biomarker reaction at the skin.

BackgroundResearch has shown that up to 33% of pressure ulcers (PUs) acquired in hospitals result from the application of a medical device. Cervical collars (C-collars) have been implicated in causing PUs, due to the mechanical force they apply to the skin. In order to improve our understanding of collar-related PUs, the present study aimed to assess the biomechanical, biochemical, and microclimate effects of C-collar design and fitting tension.MethodsA cohort of 15 healthy volunteers was fit with two different C-collars according to the manufacturer guidelines. Two further collar tensions were also defined as loose and tight for each device. Each collar condition was applied for 15 minutes, with a 10 minute refractory period. Measurements at the device–skin interface included interface pressures, inflammatory biomarkers, microclimate, range of cervical motion, and comfort scores.ResultsThe interface pressures at each tissue site increased monotonically with greater collar tension (p<0.01), irrespective of collar design. Biomarker analysis revealed that inflammatory cytokines (IL-1a) were elevated during collar application, with the highest increase during the tight fit condition, representing over a fourfold increase from unloaded conditions. Regardless of collar tension or type, there was an increase in temperature 1.5°C ±0.8°C compared to baseline values. Range of motion significantly decreased with greater strap tension (p<0.05), with an associated increase in discomfort.ConclusionThe present findings revealed that increasing C-collar tensions caused elevated contact pressures at the device–skin interface, with a corresponding inflammatory response at the skin. These peak contact pressures were highest at the occiput, corresponding with reported PU locations. Devices should be designed to uniformly distribute pressures, and appropriate guidance is needed for their application.

Investigating the effects of strap tension during non-invasive ventilation mask application: a combined biomechanical and biomarker approach.

Non-invasive ventilation is commonly used for respiratory support. However, in some cases, mask application can cause pressure ulcers to specific features of the face, resulting in pain and reduced quality of life for the individual. This study investigated the effects of mask strap tension on the biomechanical and biomarker responses at the skin interface. Healthy participants (n = 13) were recruited and assigned two different masks in a random order, which were fitted with three strap conditions representing increments of 5 mm to increase tension. Masks were worn for 10 minutes at each tension followed by a 10-minute refractory period. Assessment at the device–skin interface included measurements of pressures at the nose and cheeks, temperature and humidity, a selection of inflammatory cytokine concentrations collected from sebum and scores of comfort. The results indicated significantly higher interface pressures at the bridge of the nose compared to the cheeks for both masks (p < 0.05), with nasal interface pressures significantly increasing with elevated strap tension (p < 0.05). One inflammatory cytokine, IL-1α, increased following mask application at the highest tension, with median increases from baselines ranging from 21 to 33%. The other cytokines revealed a less consistent trend with strap tension. The participants reported statistically greater discomfort during elevated strap tension. Temperature and humidity values under the mask were elevated from ambient conditions, although no differences were observed between mask type or strap tension. The bony prominence on the bridge of the nose represented a vulnerable area of skin during respiratory mask application. This study has shown that mask strap tension has a significant effect on the pressure exerted on the nose. This can result in discomfort and an inflammatory response at the skin surface. Further studies are required to investigate respiratory mask application for appropriate individuals with comorbidities.

Initial Tourniquet Pressure Does Not Affect Tourniquet Arterial Occlusion Pressure

Effective nonelastic strap-based tourniquets are typically pulled tight and friction or hook-and-loop secured before engaging a mechanical advantage system to reach arterial occlusion pressure. This study examined the effects of skin surface initial secured pressure (Friction Pressure) on the skin surface pressure applied at arterial occlusion (Occlusion Pressure) and on the use of the mechanical advantage system.Combat Application Tourniquets(®) (CATs; combattourniquet.com) and Tactical Ratcheting Medical Tourniquets (RMTs; www .ratchetingbuckles.com) were applied to 12 recipient thighs with starting Friction Pressures of 25 (RMT only), 50, 75, 100, 125, 150, 175 (CAT only), and 200mmHg (CAT only). The CAT strap was single threaded. Pressure was measured with an air-filled, size #1, neonatal blood pressure cuff under the Base (CAT), Ladder (RMT), and Strap (CAT and RMT) of each 3.8cm-wide tourniquet.Base or Ladder pressure and Strap pressure were related but increasingly different at increasing pressures, with Strap pressures being lower (Friction Pressure, r > 0.91; Occlusion Pressure, r > 0.60). Friction Pressure did not affect Occlusion Pressure for either design. Across the 12 thighs, the correlation coefficient for Strap Friction Pressure versus CAT windlass turns was r = -0.91 ± 0.04, and versus RMT ladder distance traveled was r = -0.94 ± 0.06. Friction Pressures of 150mmHg or greater were required to achieve CAT Occlusion with two or fewer windlass turns. CAT and RMT Strap Occlusion Pressures were similar on each recipient (median, minimum - maximum; CAT: 318mmHg, 260 - 536mmHg; RMT: 328mmHg, 160 - 472mmHg).Achieving high initial strap tension is desirable to minimize windlass turns or ratcheting buckle travel distance required to reach arterial occlusion, but does not affect tourniquet surface-applied pressure needed for arterial occlusion. For same-width, nonelastic strap-based tourniquets, differences in the mechanical advantage system may be unimportant to final tourniquet-applied pressure needed for arterial occlusion.

Component Analysis of Respirator User Training

Respirators must be properly used to be effective. In an experimental protocol, 145 subjects were trained and then observed donning and doffing respirators. Filtering facepiece and dual cartridge half face mask types were studied. Subjects were then tested for knowledge and for proper performance using video recording analysis. Knowledge tests showed adequate learning, but performance was often poor. Inspection, strap tension (half mask), seal checking, and avoiding mask contact during doffing were particularly problematic. Mask positioning was generally well done. Correlation between knowledge and performance for specific items was generally poor, although there was a weak correlation between overall knowledge and overall performance (rho = 0.32) for the half mask users. Actual unprompted performance as well as knowledge and fit-testing should be assessed for user certification. Respirator design approval should consider users' ability to learn proper technique.

Scapular Bracing and Alteration of Posture and Muscle Activity in Overhead Athletes With Poor Posture

Overhead athletes commonly have poor posture. Commercial braces are used to improve posture and function, but few researchers have examined the effects of shoulder or scapular bracing on posture and scapular muscle activity. To examine whether a scapular stabilization brace acutely alters posture and scapular muscle activity in healthy overhead athletes with forward-head, rounded-shoulder posture (FHRSP). Randomized controlled clinical trial. Applied biomechanics laboratory. Thirty-eight healthy overhead athletes with FHRSP. Participants were assigned randomly to 2 groups: compression shirt with no strap tension (S) and compression shirt with the straps fully tensioned (S + T). Posture was measured using lateral-view photography with retroreflective markers. Electromyography (EMG) of the upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA) in the dominant upper extremity was measured during 4 exercises (scapular punches, W's, Y's, T's) and 2 glenohumeral motions (forward flexion, shoulder extension). Posture and exercise EMG measurements were taken with and without the brace applied. Head and shoulder angles were measured from lateral-view digital photographs. Normalized surface EMG was used to assess mean muscle activation of the UT, MT, LT, and SA. Application of the brace decreased forward shoulder angle in the S + T condition. Brace application also caused a small increase in LT EMG during forward flexion and Y's and a small decrease in UT and MT EMG during shoulder extension. Brace application in the S + T group decreased UT EMG during W's, whereas UT EMG increased during W's in the S group. Application of the scapular brace improved shoulder posture and scapular muscle activity, but EMG changes were highly variable. Use of a scapular brace might improve shoulder posture and muscle activity in overhead athletes with poor posture.

Validation of a Miniature Thermochron for Monitoring Thoracolumbosacral Orthosis Wear Time

Prospective validation study. To establish the accuracy of miniature thermochrons for estimating thoracolumbosacral orthosis (TLSO) wear time in patients with adolescent idiopathic scoliosis. There has been an emphasis in recent years on measuring wear time as opposed to using subjective methods such as relying on the patient or parent estimation. By measuring the amount of time that was spent in the orthosis, uncertainty is reduced and the validity of the research is improved. Several types of devices have been employed for direct monitoring of orthosis wear time including strap tension monitors, pressure sensors, and temperature-time sensors (thermochrons). Direct monitoring studies have shown that relying on patient or parent report is inaccurate; the patient/parent report is clearly biased towards overestimation of wear time. Three miniature thermochrons (DS1922L iButton, Maxim Integrated Products, Inc., Sunnyvale, CA) were mounted underneath padding in the TLSOs of 7 participants diagnosed with adolescent idiopathic scoliosis. The participants wore their TLSO for 1 month. During this time, participants kept meticulous records of wear time in diaries. An algorithm was developed to automatically detect donning/doffing of the orthosis, and the results of the data reduction algorithm were compared with the diary (gold standard). Total wear time accuracy was 98.5% (0.37 hours/day), while the precise timing of donning/doffing was 92% accurate. An inexpensive, commercially available miniature thermochron and a simple robust algorithm can estimate TLSO wear time to a high degree of accuracy. This method is suitable for large-scale prospective studies examining the efficacy of bracing in adolescent idiopathic scoliosis, which remains a topic of controversy.

Study of the corrective forces applied by a dynamic derotation brace (DDB)

Background and purpose The direct forces exerted by the brace pad were analysed, on 44 idiopathic scoliotic patients (38 girls, 6 boys) treated with a DDB [1]. Twenty seven patients had a single right thoracic curve and 17 had a single left or right thoracolumbar curve. The aim was the analysis of the corrective forces, exerted at the skin-brace interface, by altering the posture, activity and strap tension [2-7].

Design and validation of transducers to measure interface force distribution in a spinal orthosis

Scoliosis is a spinal deformity that affects millions of adolescents in the United States. Bracing is the most common non-surgical treatment method for scoliosis, but the biomechanics of such treatment is unclear. The objective of this study is to develop and validate a force logging system that can record forces at multiple locations inside a brace, as well as brace strap tension, and correlate these forces with different body positions. The force logging system can be used to investigate the biomechanics function of a brace to treat scoliosis during the treatment period.Two phases were completed in this study: design phase, involving custom development and calibration of strap tension transducers and modifications of in-brace force transducers; and validation phase, including preliminary testing on a subject with different postures.In-brace force load cell and tension transducer were tested and validated. Their sensitivities were 193.5±4.9mV/N and 35.5±0.2mV/N, respectively, with both linear correlation coefficients were 0.99, reflecting high repeatability and linearity. Qualitative validation was also completed, allowing general relationships to be found between subject posture and force distribution. This study shows an excellent functionality and utility of the developed system.

Analysis of the corrective forces exerted by a dynamic derotation brace (DDB)

Discrepancies exist in the current literature for bracing of spinal curvature conditions. This can be explained by the diversity of brace types, the different curve patterns and the various measurement methods and instruments. The aim of this study was the analysis of the corrective forces exerted by a dynamic derotation brace (DDB), at the skin-brace interface, altering the strap tension and body posture. We analysed the direct forces exerted by a DDB's main pad, on 44 (38 girls, 6 boys) idiopathic scoliotic patients. Twenty-seven patients had a single right thoracic and 17 a single left or right thoracolumbar curve. We used the F-Socket 9801 pressure sensor and the MatScan Research BETA STAM 6.30 software, while patients adopted nine different postures. The patients were divided into three different groups: those who wore the brace for the first time, those who were changing their brace for a new one, and those who were having adjustments made to their existing brace. These patients who were having adjustments made to their existing brace caused the highest mean exerted force. Changes in strap tension and body posture resulted in statistically significant alterations of the interface pressure and the forces exerted on the patient's body. Tightening the brace's straps always produces a significant force increase, independent of the body posture and the curve type. Also there are some body postures which significantly modify the exerted force. The body posture of maximum inspiration for thoracolumbar curves and, additionally, prone and lying left for thoracic curves.

Sensitivity analysis of important parameters affecting contact pressure between a respirator and a headform

Respirator comfort and fit are two important parameters for respirator design, usage, and standard development. The contact pressure (as measured between a respirator and the wearer) plays an important role in comfort and fit. This work attempts to investigate the contact mechanism and factors that affect the contact pressure. This paper focuses on mechanical factors such as strap tension, strap orientation, strap location, friction, and seal material. A finite element (FE) model-based method was developed to assess the contact pressure. The FE models for both the headform and the respirator have multiple layers. The headform is a medium size headform developed by the National Institute for Occupational Safety and Health (NIOSH) and the respirator is an MSA Affinity Ultra respirator. The results show that the positive Z directional force of strap tension that forces the respirator to move towards the headform is the most important parameter for measuring pressure distribution. Other factors such as strap orientation, friction, strap location, and softness of the seal material were found to affect the contact pressure distribution in this study. Strap orientation and friction coefficient have no significant effect on maximum pressure and maximum shear stress. The dispersive strap location increased the contact pressure on the nose-bridge area of the wearer, while concentrated location had no considerable effect on contact pressure. A softer seal material causes larger deformations and transfers the location of the maximum pressure from the nose-bridge to the tip of the nose. Relevance to industry This study investigates the effect of important parameters on contact pressure between a respirator and a headform. The sensitivity analysis can provide insights of the interaction between a respirator and a headform. The findings are critical to respirator designers, users, and standard developers to ensure maximal respirator fit and comfort.