Medical Engineering & Physics - Articles in Press

Nonlinear analysis of actigraphic signals for the assessment of the attention-deficit/hyperactivity disorder (ADHD) - Corrected Proof

2012-02-02

Abstract: Attention-deficit/hyperactivity disorder (ADHD) is the most common neurobehavioral disorder in children and adolescents; however, its etiology is still unknown, which hinders the existence of reliable, fast and inexpensive standard diagnostic methods. In this paper, we propose a novel methodology for automatic diagnosis of the combined type of ADHD based on nonlinear signal processing of 24h-long actigraphic registries. Since it relies on actigraphy measurements, it constitutes an inexpensive and non-invasive objective diagnostic method. Our results on real data reach 96.77% sensitivity and 84.38% specificity by means of multidimensional classifiers driven by combined features from different time intervals. Our analysis also reveals that, if features from a single time interval are used, the whole 24-h interval is the only one that yields classification figures with practical diagnostic capabilities. Overall, our figures overcome those obtained by actigraphy-based methods reported and are comparable with others based on more expensive (and not so convenient) adquisition methods.

Deformation behavior of the iliotibial tract under different states of fixation - Corrected Proof

2012-02-01

Abstract: Background and objective: The iliotibial tract (tract) is an important structure for the biomechanics of both the hip and knee joint. While a detailed characterization of its mechanical properties might help to better understand its specific role in the load transfer from the pelvis to femur and tibia, determination of those properties is complicated by its particular structure of thin fibers in the fresh state. Moreover, although the tracts mechanical properties are often derived from cadaveric material chemically fixed with either ethanol or formaldehyde, the influence of such fixation methods remains to be elucidated. Aim of this study was to determine Young's modulus (tensile modulus, YM) of the tract. We hypothesized that either ethanol or formaldehyde fixation would significantly increase the YM compared to the tracts condition in a fresh state.Material and methods: 13 specimens of tract were gained from donators. The ends of the probes were plastinated with resin creating a sharp interface between the clamp and the probe to prevent material slippage. The specimens were measured in their fresh state, under ethanol- and formaldehyde-fixed conditions and re-measured after rinsing with tap water.Results: The YM of the fresh probes averaged 397.3N/mm2 with a standard deviation (SD) of 151.5N/mm2. The YM of the ethanol-fixed specimens was significantly higher (673.2N/mm2, SD 328.5N/mm2, p<0.05). After rinsing with tap water, the YM decreased to 95% of the fresh condition value (377.4N/mm2, SD 144.5N/mm2, non-significant change from fresh). After formaldehyde fixation, the YM reached 490.3N/mm2 (SD 143.0N/mm2, p<0.05). When the formaldehyde-fixed specimens were rinsed, the YM was 114% of the value of the fresh condition (452.6N/mm2, SD 115.1N/mm2, non-significant change from fresh).Conclusions: This study found a significant influence of the chemical fixation method on the YM of the IT tract. If such fixation is required, our results suggest using a treatment with ethanol and subsequent rinsing that results in minimal changes to the tracts YM. Furthermore, plastination of the ends of the specimens could be crucial to allow in vitro determination of valid YM of ligaments data that can then be integrated with confidence in further finite element analyses.

The accuracy and repeatability of an automatic 2D–3D fluoroscopic image-model registration technique for determining shoulder joint kinematics - Corrected Proof

Zhonglin Zhu, Daniel F. Massimini, Guangzhi Wang, Jon J.P. Warner, Guoan Li — 2012-01-30

Abstract: Fluoroscopic imaging, using single plane or dual plane images, has grown in popularity to measure dynamic in vivo human shoulder joint kinematics. However, no study has quantified the difference in spatial positional accuracy between single and dual plane image-model registration applied to the shoulder joint. In this paper, an automatic 2D–3D image-model registration technique was validated for accuracy and repeatability with single and dual plane fluoroscopic images. Accuracy was assessed in a cadaver model, kinematics found using the automatic registration technique were compared to those found using radiostereometric analysis. The in vivo repeatability of the automatic registration technique was assessed during the dynamic abduction motion of four human subjects. The in vitro data indicated that the error in spatial positional accuracy of the humerus and the scapula was less than 0.30mm in translation and less than 0.58° in rotation using dual plane images. Single plane accuracy was satisfactory for in-plane motion variables, but out-of-plane motion variables on average were approximately 8 times less accurate. The in vivo test indicated that the repeatability of the automatic 2D–3D image-model registration was 0.50mm in translation and 1.04° in rotation using dual images. For a single plane technique, the repeatability was 3.31mm in translation and 2.46° in rotation for measuring shoulder joint kinematics. The data demonstrate that accurate and repeatable shoulder joint kinematics can be obtained using dual plane fluoroscopic images with an automatic 2D–3D image-model registration technique; and that out-of-plane motion variables are less accurate than in-plane motion variables using a single plane technique.

Shear force measurements on low- and high-stiffness posterior fusion devices - Corrected Proof

2012-01-27

Abstract: Low-stiffness posterior fusion devices for the lumbar spine have been developed to treat degenerative spinal conditions. However, the demands on an implant vary between a stable motion segment and one which exhibits a significant degree of sagittal plane instability. Shear motion in the antero-posterior direction is a relevant mode of instability for clinical conditions such as degenerative lumbar spondylolisthesis. Shear load-sharing between the implant and spine in conditions of antero-posterior instability has not been studied, nor have there been comparisons between traditional rigid implants and novel low-stiffness implants. The objective of this study was to develop a method to measure in vitro shear forces on three clinically relevant fusion implants when they are applied to an unstable model of degenerative spondylolisthesis in a human cadaver spine. Uniaxial strain gauges were affixed to the surface of the implants and a spine-segment-specific calibration method was used to calibrate the strain output to an applied shear force. The accuracy of the force measurements was within 3.4N for all implant types and the repeatability was within 5.4N. The force measurement technique was sufficiently accurate and reliable to conclude that it is suitable for use in in vitro experiments to measure implant shear force.

Mechanical and functional assessment of the wrist affected by rheumatoid arthritis: A finite element analysis - Corrected Proof

M.N. Bajuri, Mohammed Rafiq Abdul Kadir, Murali Malliga Raman, T. Kamarul — 2012-01-25

Abstract: Understanding the pathomechanics involved in rheumatoid arthritis (RA) of the wrist provides valuable information, which will invariably allow various therapeutic possibilities to be explored. The computational modelling of this disease permits the appropriate simulation to be conducted seamlessly. A study that underpins the fundamental concept that produces the biomechanical changes in a rheumatoid wrist was thus conducted through the use of finite element method. The RA model was constructed from computed tomography datasets, taking into account three major characteristics: synovial proliferation, cartilage destruction and ligamentous laxity. As control, a healthy wrist joint model was developed in parallel and compared. Cartilage was modelled based on the shape of the articulation while the ligaments were modelled with linear spring elements. A load-controlled analysis was performed simulating physiological hand grip loading conditions. The results demonstrated that the diseased model produced abnormal wrist extension and stress distribution as compared to the healthy wrist model. Due to the weakening of the ligaments, destruction of the cartilage and lower bone density, the altered biomechanical stresses were particularly evident at the radioscaphoid and capitolunate articulations which correlate to clinical findings. These results demonstrate the robust finding of the developed RA wrist model, which accurately predicted the pathological process.

Developing an efficient and reliable dry powder inhaler for pulmonary drug delivery – A review for multidisciplinary researchers - Corrected Proof

Nazrul Islam, Matthew J. Cleary — 2012-01-25

Abstract: Pulmonary drug delivery is the focus of much research and development because of its great potential to produce maximum therapeutic benefit. Among the available options the dry powder inhaler (DPI) is the preferred device for the treatment of an increasingly diverse number of diseases. However, as drug delivery from a DPI involves a complicated set of physical processes and the integration of drug formulations, device design and patient usage, the engineering development of this medical technology is proving to be a great challenge. Currently there is large range of devices that are either available on the market or under development, however, none exhibit superior clinical efficacy. A major concern is the inter- and intra-patient variability of the drug dosage delivered to the deep lungs. The extent of variability depends on the drug formulation, the device design and the patient's inhalation profile. This article reviews recent advances in DPI technology and presents the key factors which motivate and constrain the successful engineering of a universal, patient-independent DPI that is capable of efficient, reliable and repeatable drug delivery. A strong emphasis is placed on the physical processes of drug powder aerosolisation, deagglomeration, and dispersion and on the engineering of formulations and inhalers that can optimise these processes.

Correlation of the experimental and numerical results for the holding power of dental, traumatic, and spinal screws - Corrected Proof

Chia-Ching Lee, Shang-Chih Lin, Shu-Wei Wu, Yu-Ching Li, Ping-Yuen Fu — 2012-01-24

Abstract: The holding power of the bone–screw interfaces is one of the key factors in the clinical performance of screw design. The value of the holding power can be experimentally measured by pullout tests. Historically, some researchers have used the finite-element method to simulate the holding power of the different screws. Among them, however, the assumed displacement of the screw withdrawal is unreasonably small (about 0.005–1.0mm). In addition, the chosen numerical indices are quite different, including maximum stress, strain energy, and reaction force. This study systematically uses dental, traumatic, and spinal screws to experimentally measure and numerically simulate their bone-purchasing ability within the synthetic bone. The testing results (pullout displacement and holding power) and numerical indices (maximum stress, total strain energy, and reaction forces) are chosen to calculate their correlation coefficients. The pullout displacement is divided into five regions from initial to final withdrawal. The experimental results demonstrate that the pullout displacement consistently occurs at the final region (0.6–1.6mm) and is significantly higher than the assumed value of the literature studies. For all screw groups, the measured holding power within the initial region is not highly or even negatively correlated with the experimental and numerical results within the final region. The observation from the simulative results shows the maximum stress only reflects the loads concentrated at some local site(s) and is the least correlated to the measured holding power. Comparatively, both energy and force are more global indices to correlate with the gross failure at the bone–screw interfaces. However, the energy index is not suitable for the screw groups with rather tiny threads compared with the other specifications. In conclusion, the underestimated displacement leads to erroneous results in the screw–pullout simulation. Among three numerical indices the reaction-force is the optimal index for the screw–pullout problem.

Investigation on the load-displacement curves of a human healthy heel pad: In vivo compression data compared to numerical results - Corrected Proof

2012-01-24

Abstract: The aims of the present work were to build a 3D subject-specific heel pad model based on the anatomy revealed by MR imaging of a subject's heel pad, and to compare the load–displacement responses obtained from this model with those obtained from a compression device used on the subject's heel pad. A 30 year-old European healthy female (mass=54kg, height=165cm) was enrolled in this study. Her left foot underwent both MRI and compression tests. A numerical model of the heel region was developed based on a 3D CAD solid model obtained by MR images. The calcaneal fat pad tissue was described with a visco-hyperelastic model, while a fiber-reinforced hyperelastic model was formulated for the skin. Numerical analyses were performed to interpret the mechanical response of heel tissues. Different loading conditions were assumed according to experimental tests. The heel tissues showed a non-linear visco-elastic behavior and the load–displacement curves followed a characteristic hysteresis form. The energy dissipation ratios measured by experimental tests (0.25±0.02 at low strain rate and 0.26±0.03 at high strain rate) were comparable with those evaluated by finite element analyses (0.23±0.01 at low strain rate and 0.25±0.01 at high strain rate). The validity and efficacy of the investigation performed was confirmed by the interpretation of the mechanical response of the heel tissues under different strain rates. The mean absolute percentage error between experimental data and model results was 0.39% at low strain rate and 0.28% at high strain rate.

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

Andrew Chan, Edmond Lou, Doug Hill, Gary Faulkner — 2012-01-20

Abstract: 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.

An optimized method for tremor detection and temporal tracking through repeated second order moment calculations on the surface EMG signal - Corrected Proof

Cristiano De Marchis, Maurizio Schmid, Silvia Conforto — 2012-01-18

Abstract: In this study, the problem of detecting and tracking tremor from the surface myoelectric signal is addressed. A method based on the calculation of a Second Order Moment Function (SOMF) inside a window W sliding over the sEMG signal is here presented. An analytical formulation of the detector allows the extraction of the optimal parameters characterizing the algorithm. Performance of the optimized method is assessed on a set of synthetic tremor sEMG signals in terms of sensitivity, precision and accuracy through the use of a properly defined cost function able to explain the overall detector performance. The obtained results are compared to those emerging from the application of optimized versions of traditional detection techniques. Once tested on a database of synthetic tremor sEMG data, a quantitative assessment of the SOMF algorithm performance is carried out on experimental tremor sEMG signals recorded from two patients affected by Essential Tremor and from two patients affected by Parkinson's Disease. The SOMF algorithm outperforms the traditional techniques both in detecting (sensitivity and positive predictive value >99% for SNR higher than 3dB) and in estimating timings of muscular tremor bursts (bias and standard deviation on the estimation of the onset and offset time instants lower than 8ms). Its independence from the SNR level and its low computational cost make it suitable for real-time implementation and clinical use.

Needle-free jet injection using real-time controlled linear Lorentz-force actuators - Corrected Proof

Andrew Taberner, N. Catherine Hogan, Ian W. Hunter — 2012-01-16

Abstract: Needle-free drug delivery by jet injection is achieved by ejecting a liquid drug through a narrow orifice at high pressure, thereby creating a fine high-speed fluid jet that can readily penetrate skin and tissue. Until very recently, all jet injectors utilized force- and pressure-generating principles that progress injection in an uncontrolled manner with limited ability to regulate delivery volume and injection depth. In order to address these shortcomings, we have developed a controllable jet injection device, based on a custom high-stroke linear Lorentz-force motor that is feed-back controlled during the time-course of an injection.Using this device, we are able to monitor and modulate continuously the speed of the drug jet, and regulate precisely the volume of drug delivered during the injection process. We demonstrate our ability to control injection depth (up to 16mm) and repeatably and precisely inject volumes of up to 250μL into transparent gels and post-mortem animal tissue.

A new method for the evaluation of dental implant stability using an inductive sensor - Corrected Proof

2012-01-12

Abstract: We developed a new method for the measurement of dental implant stability by analyzing the impulse response of the implant. The movement of the implant was measured by an inductive sensor with a dedicated adaptor. The large inductance of the adapter amplified the small displacement signal of the implant. The Periotest (Siemens, Bensheim, Germany) was used as a source of excitation force to acquire the impact response of the implant. Power spectrum analysis was applied to the impact response of the implant. The peak frequency of the spectrum was used as a measure of the implant stability. The performance of the system was tested and verified through simulation of the implant–bone interface in an in vitro model. Various implant–bone interfacial conditions were assessed. Holes of varying depth and diameter were drilled into a dental implantation model. Two types of impression materials (EXAMIXFINE, Regisil Rigid) with different degrees of hardness were used to fix the implant into the hole. The implant stability was also measured using the ISQ (implant stability quotient) by resonance frequency analysis on the Osstell Mentor (Integration Diagnostics AB, Goteborgsvagen, Sweden) for comparison. Linear regression analysis of the peak frequency as a stability parameter showed a linear relationship with both the depth and the diameter of the hole (p<0.05). When EXAMIXFINE was used, the peak frequency was linearly associated with the depth (R2=0.443) and diameter (R2=0.396) of the hole. When Regisil Rigid was used, the peak frequency also showed a linear relationship with the depth (R2=0.555) and diameter (R2=0.350) of the hole. The peak frequency also increased as the hardness of the impression material increased. Differentiability of the system was evaluated by an ANOVA test. A statistically significant difference (p<0.01) was found between all implantation conditions, except in one case using the Regisil Rigid material. In contrast, the ISQ value did not consistently differentiate under several implantation conditions. The developed method could differentiate the stability changes in simulated implantation conditions with a wider dynamic range and with higher resolution than the ISQ value.

Movement quantification in epileptic seizures: A feasibility study for a new 3D approach - Corrected Proof

2012-01-09

Abstract: Movement quantification of the human body is presently used for analyzing deficits resulting from Central Nervous System (CNS) pathologies or exploring the insights of the human motor system behaviour. Following our previous work on 2D movement quantification of epileptic seizures, we now present a feasibility study for a newly developed 3D technique. In order to validate this new 3D approach we made a comparison with the previous method. Both techniques were tested in two different datasets: a simple motor execution performed by a volunteer and a complex motor motion induced by a real epileptic seizure. The results obtained showed, as expected, the superior robustness and precision of the 3D approach but also confirmed the validity of the 2D method, given certain constraints. We conclude that the newly developed 3D system will highly improve our capacity of pursuing the clinical research on quantitative characterization of seizure semiology to support epilepsy diagnosis.

Influences of supra-physiological temperatures on microstructure and mechanical properties of skin tissue - Corrected Proof

Min Lin, Xiao Zhai, Shuqi Wang, Zhengjin Wang, Feng Xu, Tian Jian Lu — 2012-01-09

Abstract: Thermal therapies under supra-physiological temperatures are increasingly used to treat skin diseases (e.g., superficial melanoma, removal of port-wine stains pigmented and cutaneous lesions). The efficacy of these therapies depends on the thermal and mechanical loadings that skin experiences during the treatment process. Therefore, it is of great significance to better understand the role of thermally induced changes in skin mechanical behavior and microstructure. In this study, rabbit belly skin was thermally damaged by immersing skin samples into saline solutions with controlled temperatures. We investigated the effect of thermal damage on skin mechanical behavior. We quantified the changes in skin microstructure (i.e., fiber, fibril) using histological staining and transmission electron microscopy (TEM). The results indicate that (i) the elastic modulus of skin, obtained by the uniaxial tensile test, decreased with increasing heating temperature; (ii) the skin tensile behavior was correlated with its microstructure changes induced by thermal denaturation of collagen fibers under supra-physiological temperatures; (iii) skin thermal damage predicted using the Arrhenius burn integration quantitatively agrees well with the evolution of the microstructure (i.e., percentage of the collagen area in Hematoxylin and Eosin (H&E) staining results). This study provides a better understanding of the coupled bio-thermo-mechanical behavior of skin tissue that could help to improve clinical thermal therapies.

Evaluation of migration forces of a retrievable filter: Experimental setup and finite element study - Corrected Proof

2012-01-09

Abstract: The aim of this paper is to provide a computational study of migration forces of a retrievable filter (Günther Tulip inferior vena cava filter). Using an experimental setup and finite element simulation, the migration forces and stress at the end of the anchored hooks in the struts were estimated. After that, the estimation value of migration stress (τrup) was used to analyze the effect of different mechanical factors (strut thickness, vena cava diameter) in the migration of the IVC filter.Our results show that the migration stress is τrup=4.37N/mm2. Using this value we obtain that the filter with higher strut diameter (ϕstrut=0.45mm) shows the maximal migration forces in every cava diameter. On the other hand, the value of the migration force decreases when the cava diameter increases. In addition, the finite element simulations also show that there are contact between the struts of the filter and the vein in regions close to the anchors.

Design and evaluation of a novel microphone-based mechanomyography sensor with cylindrical and conical acoustic chambers - Corrected Proof

A.O. Posatskiy, T. Chau — 2012-01-09

Abstract: Mechanomyography has recently been proposed as a control modality for alternative access technologies for individuals with disabilities. However, MMG recordings are highly susceptible to contamination from limb movements. Pressure-based transducers are touted to be the most robust to external movement although there is some debate about their optimal chamber geometry, in terms of low frequency gain and spectral flatness.To investigate the question of preferred geometry, transducers with cylindrical and conical chambers of varying dimensions were designed, manufactured and tested. Using a computer-controlled electrodynamic shaker, the frequency response of each chamber geometry was empirically derived.Of the cylindrical chambers, the highest gain and the flattest frequency response was exhibited by a chamber 10mm in diameter and 5–7mm in height. However, conical chambers offered an average rise in gain of 6.79±1.06dB/Hz over that achievable with cylindrical geometries. The highest gain and flattest response was achieved with a transducer consisting of a low-frequency MEMS microphone, a 4μm aluminized mylar membrane and a rigid conical chamber 7mm in diameter and 5mm in height. This design is recommended for MMG applications where limb movement is prevalent.

Multiclass classification of subjects with sleep apnoea–hypopnoea syndrome through snoring analysis - Corrected Proof

Jordi Solà-Soler, José Antonio Fiz, José Morera, Raimon Jané — 2012-01-09

Abstract: The gold standard for diagnosing sleep apnoea–hypopnoea syndrome (SAHS) is polysomnography (PSG), an expensive, labour-intensive and time-consuming procedure. Accordingly, it would be very useful to have a screening method to allow early assessment of the severity of a subject, prior to his/her referral for PSG. Several differences have been reported between simple snorers and SAHS patients in the acoustic characteristics of snoring and its variability. In this paper, snores are fully characterised in the time domain, by their sound intensity and pitch, and in the frequency domain, by their formant frequencies and several shape and energy ratio measurements. We show that accurate multiclass classification of snoring subjects, with three levels of SAHS, can be achieved on the basis of acoustic analysis of snoring alone, without any requiring information on the duration or the number of apnoeas. Several classification methods are examined. The best of the approaches assessed is a Bayes model using a kernel density estimation method, although good results can also be obtained by a suitable combination of two binary logistic regression models. Multiclass snore-based classification allows early stratification of subjects according to their severity. This could be the basis of a single channel, snore-based screening procedure for SAHS.

An innovative approach of QRS segmentation based on first-derivative, Hilbert and Wavelet Transforms - Corrected Proof

2012-01-09

Abstract: The QRS detection and segmentation processes constitute the first stages of a greater process, e.g., electrocardiogram (ECG) feature extraction. Their accuracy is a prerequisite to a satisfactory performance of the P and T wave segmentation, and also to the reliability of the heart rate variability analysis. This work presents an innovative approach of QRS detection and segmentation and the detailed results of the proposed algorithm based on First-Derivative, Hilbert and Wavelet Transforms, adaptive threshold and an approach of surface indicator. The method combines the adaptive threshold, Hilbert and Wavelet Transforms techniques, avoiding the whole ECG signal preprocessing. After each QRS detection, the computation of an indicator related to the area covered by the QRS complex envelope provides the detection of the QRS onset and offset. The QRS detection proposed technique is evaluated based on the well-known MIT-BIH Arrhythmia and QT databases, obtaining the average sensitivity of 99.15% and the positive predictability of 99.18% for the first database, and 99.75% and 99.65%, respectively, for the second one. The QRS segmentation approach is evaluated on the annotated QT database with the average segmentation errors of 2.85±9.90ms and 2.83±12.26ms for QRS onset and offset, respectively. Those results demonstrate the accuracy of the developed algorithm for a wide variety of QRS morphology and the adaptation of the algorithm parameters to the existing QRS morphological variations within a single record.

Bone remodelling analysis of the humerus after a shoulder arthroplasty - Corrected Proof

Carlos Quental, João Folgado, Paulo R. Fernandes, Jacinto Monteiro — 2012-01-05

Abstract: The shoulder arthroplasty has become an efficient treatment for some pathologies. However there are complications that can compromise its success. Among them, the stress shielding effect on the humerus has been reported as a possible cause of failure. The objective of this work was to investigate the bone remodelling in the humerus after a shoulder arthroplasty. For this purpose, computational models were developed to analyse the stress shielding contribution to the humeral component failure of shoulder arthroplasties, with a cemented and an uncemented prosthesis. A computational remodelling model was used to characterize the bone apparent density at each site of the humerus. The density distribution was obtained by the solution of a problem that takes into account both structural stiffness and the metabolic cost of bone maintenance. Bone was subjected to 6 load cases that include the glenohumeral reaction force and the action of 10 muscles. In the implanted models, different interface conditions were tested for the bone–implant and the cement–implant interfaces. Moreover, a pathological case defined by a poorer quality of bone was considered. In the healthy situation, the models that better model in vivo conditions showed no significant changes in bone mass. However, the results for the pathological case showed some bone resorption which supports the importance given to the quality of bone in the success of the joint replacement. Bearing in mind the conditions addressed, the results lead to conclude that the stress shielding is not a key factor for the humeral component failure of shoulder arthroplasties in a healthy situation though several issues, including muscle function and bone quality, may heighten its effect.

Computational analysis of the flow of bile in human cystic duct - Corrected Proof

Mushtak Al-Atabi, R.C. Ooi, X.Y. Luo, S.B. Chin, N.C. Bird — 2012-01-04

Abstract: Computational fluid dynamic (CFD) simulations of the three-dimensional flow structures in realistic cystic ducts have been performed to obtain quantitative readings of the flow parameters to compare with clinical measurements. Resin casts of real patients’ cystic ducts lumen that possess representative anatomical features were scanned to obtain three-dimensional flow domains that were used in the numerical analysis. The convoluting nature of the studied cystic ducts resulted in strong secondary flow that contributed towards a dimensionless pressure drop that is four times higher than those of a straight circular tube of an equivalent length and average diameter. The numerical pressure drop results across the cystic duct compared very well with those obtained from clinical observations which indicate that CFD is an appropriate tool to investigate the flow and functions of the biliary system. From the hydrodynamic point of view, the cystic duct lumen seems to serve as a passive resistor that strives to provide a constant amount of resistance to control the flow of bile out of the gallbladder. This is mainly achieved by the coupling of the secondary flow effects and bile rheology to provide flow resistance.

A comprehensive three-dimensional dynamic model of the human head and trunk for estimating lumbar and cervical joint torques and forces from upper body kinematics - Corrected Proof

Albert H. Vette, Takashi Yoshida, T. Adam Thrasher, K. Masani, Milos R. Popovic — 2012-01-03

Abstract: Linked-segment representations of human body dynamics have been used extensively in biomechanics, ergonomics, and rehabilitation research to systemize thinking, make predictions, and suggest novel experiments. In the scope of upper body biomechanics, these models play an even more essential role as the human spine dynamics are difficult to study in vivo. No study exists to date, however, that specifically disseminates the technical details of a comprehensive three-dimensional model of the upper body for the purpose of estimating spinal joint torques and forces for a wide range of scenarios. Consequently, researchers are still bound to develop and implement their own models. Therefore, the objective of this study was to design a dynamic model of the upper body that can comprehensively estimate spinal joint torques and forces from upper body kinematics. The proposed three-dimensional model focuses on the actions of the lumbar and cervical vertebrae and consists of five lumbar segments (L1 to L5), the thorax, six cervical segments (C2 to C7), and the head. Additionally, the model: (1) is flexible regarding the kinematic nature of the spinal joints (free, constrained, or fixed); (2) incorporates all geometric and mass-inertia parameters from a single, high-resolution source; and (3) can be feasibly implemented via different inverse dynamics formulations. To demonstrate its practicality, the model was finally employed to estimate the lumbar and cervical joint torques during perturbed sitting using experimental motion data. Considering the growing importance of mathematical predictions, the developed model should become an important resource for researchers in different fields.

A novel method for the generation of multi-block computational structured grids from medical imaging of arterial bifurcations - Corrected Proof

Evangelos Makris, Panagiotis Neofytou, Sokrates Tsangaris, Christos Housiadas — 2012-01-03

Abstract: In this study a description of a new approach, for the generation of multi-block structured computational grids on patient-specific bifurcation geometries is presented. The structured grid generation technique is applied to data obtained by medical imaging examination, resulting in a surface conforming, high quality, multi-block structured grid of the branching geometry. As a case study application a patient specific abdominal aorta bifurcation is selected. For the evaluation of the grid produced by the novel method, a grid convergence study and a comparison between the grid produced by the method and unstructured grids produced by commercial meshing software are carried out.

Quantifying turbulent wall shear stress in a subject specific human aorta using large eddy simulation - Corrected Proof

Jonas Lantz, Roland Gårdhagen, Matts Karlsson — 2011-12-30

Abstract: In this study, large-eddy simulation (LES) is employed to calculate the disturbed flow field and the wall shear stress (WSS) in a subject specific human aorta. Velocity and geometry measurements using magnetic resonance imaging (MRI) are taken as input to the model to provide accurate boundary conditions and to assure the physiological relevance. In total, 50 consecutive cardiac cycles were simulated from which a phase average was computed to get a statistically reliable result. A decomposition similar to Reynolds decomposition is introduced, where the WSS signal is divided into a pulsating part (due to the mass flow rate) and a fluctuating part (originating from the disturbed flow). Oscillatory shear index (OSI) is plotted against time-averaged WSS in a novel way, and locations on the aortic wall where elevated values existed could easily be found. In general, high and oscillating WSS values were found in the vicinity of the branches in the aortic arch, while low and oscillating WSS were present in the inner curvature of the descending aorta. The decomposition of WSS into a pulsating and a fluctuating part increases the understanding of how WSS affects the aortic wall, which enables both qualitative and quantitative comparisons.

Grasping soft tissue by means of vacuum technique - Corrected Proof

D. Vonck, J.J. Jakimowicz, H.P. Lopuhaä, R.H.M. Goossens — 2011-12-28

Abstract: Introduction: A notable characteristic of bariatric surgery is the frequent manipulation of the bowel. The bowel is large, delicate, flexible, and has a natural lubricant on the tissue surface. Therefore the bowel is difficult to grasp and manipulate. Vacuum technique is commonly used in industry for all types of grasping and manipulation. Two types of nozzles that differed slightly in geometry (NT1 and NT2), were reviewed in an experimental set up for pull tests on pig bowels.Materials and methods: An experimental set-up was used to conduct a series of pull tests on pig bowel tissue. The basic principle of the measurements was a Newton's force balance; FPmax=Δp×A. Student t-tests, two-way ANOVA and Wilcoxon signed rank tests were conducted for the statistical analysis of NT1 and NT2 with regard to the maximum pull force (FPmax).Results: Concerning NT1 the Newton's force balance could not be confirmed. Concerning NT2 the Newton's force balance could partly be confirmed. For both nozzle types the effect of Δp on FPmax was significant. FPmax increases linear in proportion as Δp increases. This relation between FPmax and Δp was confirmed by the Newton's force balance.Discussion: The results confirm that vacuum technique can be used as a grasp technique for soft organs, particularly the bowels. By means of a clever design of the nozzle a firm grip can be obtained on the bowel segments. Therefore vacuum technique should be studied for further development of instruments, graspers and retractors, to be used in the abdominal area.

Experimental investigation of the reciprocating ball pump (RBP) - Corrected Proof

C.F. Lieu, W.K. Chan, K.T. Ooi — 2011-12-28

Abstract: This paper presents experimental investigations of a novel miniature reciprocating ball pump (RBP) as a potential infusion pump or drug delivery system. The objectives of this study are to validate the RBP's operational principle and to evaluate its performance. In the tests, the basic functionality of the pump has been established at different pumping frequencies ranging from 1.667Hz (100rpm) to 4.167Hz (250rpm) against different pressure heads ranging from 0mmH2O and 100mmH2O. In addition, experimental results show that the RBP can deliver a higher flow rate with a volumetric efficiency of 120% as compared to a conventional single acting reciprocating pump running under the same operating conditions.

Principles of obstacle avoidance with a transfemoral prosthetic limb - Corrected Proof

Helco G. van Keeken, Aline H. Vrieling, At L. Hof, Klaas Postema, Bert Otten — 2011-12-26

Abstract: In this study, conditions that enable a prosthetic knee flexion strategy in transfemoral amputee subjects during obstacle avoidance were investigated. This study explored the hip torque principle and the static ground principle as object avoidance strategies. A prosthetic limb simulator device was used to study the influence of applied hip torques and static ground friction on the prosthetic foot trajectory. Inverse dynamics were used to calculate the energy produced by the hip joint. A two-dimensional forward dynamics model was used to investigate the relation between obstacle–foot distance and the necessary hip torques utilized during obstacle avoidance. The study showed that a prosthetic knee flexion strategy was facilitated by the use of ground friction and by larger active hip torques. This strategy required more energy produced by the hip compared to a knee extension strategy. We conclude that when an amputee maintains enough distance between the distal tip of the foot and the obstacle during stance, he or she produces sufficiently high, yet feasible, hip torques and uses static ground friction, the amputee satisfies the conditions for enable stepping over an obstacle using a knee flexion strategy.

New method for determining in vitro structure stiffness of ceramic acetabular liners under different impact conditions - Corrected Proof

Stefan Eichhorn, Erwin Steinhauser, Reiner Gradinger, Rainer Burgkart — 2011-12-26

Abstract: Increasing both patient mobility and prosthesis life span requires improvements in the range of motion and wear behavior of the liner. With the use of new composite alumina–zirconia ceramic materials, the same stability of the liner can be achieved at lower wall thickness than it is possible with alumina-only materials. The aim of this study was developing a method for determining the in vitro structure stiffness of ceramic acetabular liners against impact stresses. The first trials were performed with a common alumina acetabular liner type (Ceramtec; Biolox forte; diameter 28mm; thickness 7mm) and a new type of alumina–zirconia (Ceramtec Biolox delta; same dimensions) liner. The clinically established alumina liner was reproducibly damaged using worst case Separation/subluxation equivalent to one-fourth or half of the head diameter, and an impact load of 15J. The liners containing the new alumina–zirconia material were not damaged in any of the trials up to an impact load of 20J and half head diameter offset.

The effect of gamma irradiation on the anisotropy of bovine cortical bone - Corrected Proof

Nicholas A. Russell, Matthew H. Pelletier, Warwick J. Bruce, William R. Walsh — 2011-12-22

Abstract: Bone is an anisotropic non-homogenous composite material composed of inorganic bone mineral embedded in an organic matrix. The mechanical behaviour of bone is governed by the volume fraction of these constituents, their mechanical properties, the degree of crystallite-collagen orientation and the bonding between phases. This study aims to evaluate the mechanical role of these constituents in the expression of anisotropy by using gamma irradiation to alter the mineralised collagen fibrils. Bovine cortical cubes were prepared, treated and mechanically tested in uniaxial compression in the axial, radial and tangential orientations. Ultimate stress, ultimate strain, energy to failure and stiffness were evaluated. This study confirmed deleterious effect of gamma irradiation on the axial compressive properties of cortical bone with a dose dependent decrease in ultimate stress of 6% (P=0.231) and 16% (P=0.001) at 15 and 25kGy respectively. This corresponded to a 39% (P=0.058) and 30% (P=0.167) reduction in energy to failure. In the radial orientation there was also a dose dependant decrease in ultimate stress which was consistent with a statistically significant decline in ultimate strain (31% (P=0.003) and 36% (P=0.000)) and energy to failure (36% (P=0.053) and 45% (P=0.008)) at both doses. In the tangential orientation there was a significant 22% (P=0.01) and 23% (P=0.02) decrease in stiffness; though these changes did not alter ultimate stress considerably. This study provides valuable insights into the role of collagen in the radial and tangential orientation when loaded in compression; while also building on the body of work related to the use of gamma irradiation for load bearing bone allografts.

A novel, inexpensive and easy to use tendon clamp for in vitro biomechanical testing - Corrected Proof

DuFang Shi, DongMei Wang, ChengTao Wang, Anmin Liu — 2011-12-21

Abstract: Frozen clamps can hold tendons and ligaments tightly and transmit high loads, from 4kN to 13kN, without slippage, yet they are complex and expensive. The existing non-frozen serrated jaw clamp is simple to fabricate and use, but the maximal tensile force it can sustain is only about 2.5kN, which is not enough in many biomechanical tests. In this study, a new type of non-frozen clamp, which has lateral block boards and asymmetrical teeth jaws, was designed. The lateral block boards made of titanium alloy were used to prevent the soft tissues from being squeezed out during compressing, while the asymmetrical teeth jaws made of nylon were used to grip and keep holding soft tissues. The capability of this new type of clamp was tested by stretching five cattle tendons to failure on the tensile and compression testing machine, none of them displayed any slippage before rupture, the maximum tension force was 6.87kN. This non-frozen asymmetrical teeth jaw clamp was designed for gripping tendons in foot and ankle dynamic simulation test, but it can also be applied to other in vitro tests, such as hip and knee dynamic tests.

Analysis of fatigue and tremor during sustained maximal grip contractions using Hilbert-Huang Transformation - Corrected Proof

Ke Li, Jean-Yves Hogrel, Jacques Duchêne, David J. Hewson — 2011-12-19

Abstract: The objective of this study was to evaluate muscle fatigue and tremor during a Sustained Maximal Grip Contraction (SMGC) using the Hilbert-Huang Transformation (HHT). Thirty-nine healthy subjects volunteered for the study and performed a 25-s SMGC. Fatigue parameters such as the relative force output (RFO) were calculated from the residual of SMGC after applying Empirical Mode Decomposition (EMD). Using the energy spectrum of the Intrinsic Mode Functions (IMF) obtained using HHT, isometric force tremor was identified from the 4 to 12Hz region in IMF3 and IMF4. Data were analysed for five consecutive 5-s epochs to identify changes in fatigue and tremor over time. The HHT method was able to identify a greater resistance to fatigue in women compared to men (p≤0.05) and in non-dominant hands compared to dominant hands (p≤0.05). Consistent with the results for fatigue, women had less tremor than men (p≤0.05), while non-dominant hands trembled less than did dominant hands (p≤0.05). Higher levels of tremor were observed for non-fatigue-resistant subjects for both 10–15s and 15–20s epochs (p≤0.05). The HHT is an appropriate method to identify both fatigue and tremor during SMGC. It would be of interest to apply this method to the study the elderly or patients with neuromuscular disorders.

Bioimpedance technique for monitoring cerebral artery stenosis in a 3D numerical model of the head - Corrected Proof

Ayelet Siegman, Shimon Abboud — 2011-12-19

Abstract: Insufficient blood supply to the brain causes a transient ischemic attack (TIA) or a stroke. One of the causes to insufficient blood supply is cerebral artery stenosis. In this study, the feasibility of bioimpedance for monitoring such stenosis was analyzed. Simulations were conducted on a realistic numerical model of the head, focusing on the left middle cerebral artery (LMCA). Tissues were assumed to act as linear isotropic volume conductors, and the quasi-static approximation was applied. Electrical potentials were calculated by solving Poisson's equation, using the finite volume method (FVM) and the successive over relaxation (SOR) method. The best sensitivity found was 0.471μV/% stenosis, using this electrode configuration: one injector near the left eye and the other injector near the right ear, one measurement position near the left eye and the other one in the right ear, keeping a distance of at least 2.5cm between measurement and injection positions. The maximal sensitivity achieved in the numerical model under the applied assumptions supports the feasibility of bioimpedance technique for monitoring cerebral artery stenosis. However, according to sensitivity [1/m4] maps, calculated for the preferable electrode configurations, the measurements’ specificity to the stenosis degree might be inadequate and should be further studied.

Review of control algorithms for robotic ankle systems in lower-limb orthoses, prostheses, and exoskeletons - Corrected Proof

R. Jiménez-Fabián, O. Verlinden — 2011-12-19

Abstract: This review focuses on control strategies for robotic ankle systems in active and semiactive lower-limb orthoses, prostheses, and exoskeletons. Special attention is paid to algorithms for gait phase identification, adaptation to different walking conditions, and motion intention recognition. The relevant aspects of hardware configuration and hardware-level controllers are discussed as well. Control algorithms proposed for other actuated lower-limb joints (knee and/or hip), with potential applicability to the development of ankle devices, are also included.

The influence of headform orientation and flooring systems on impact dynamics during simulated fall-related head impacts - Corrected Proof

Alexander D. Wright, Andrew C. Laing — 2011-12-15

Abstract: Novel compliant flooring systems are a promising approach for reducing fall-related injuries in seniors, as they may provide up to 50% attenuation in peak force during simulated hip impacts while eliciting only minimal influences on balance. This study aimed to determine the protective capacity of novel compliant floors during simulated ‘high severity’ head impacts compared to common flooring systems.A headform was impacted onto a common Commercial-Carpet at 1.5, 2.5, and 3.5m/s in front, back, and side orientations using a mechanical drop tower. Peak impact force applied to the headform (Fmax), peak linear acceleration of the headform (gmax) and Head Injury Criterion (HIC) were determined. For the 3.5m/s trials, backwards-oriented impacts were associated with the highest Fmax and HIC values (p<0.001); accordingly, this head orientation was used to complete additional trials on three common floors (Resilient Rubber, Residential-Loop Carpet, Berber Carpet) and six novel compliant floors at each impact velocity. ANOVAs indicated that flooring type was associated with all parameters at each impact velocity (p<0.001). Compared to impacts on the Commercial Carpet, Dunnett's post hoc indicated all variables were smaller (25–80%) for the novel compliant floors (p<0.001), but larger for Resilient Rubber (31–159%, p<0.01).This study demonstrates that during ‘high severity’ simulated impacts, novel compliant floors can substantially reduce the forces and accelerations applied to a headform compared to common floors including carpet and resilient rubber. In combination with reports of minimal balance impairments, these findings support the promise of novel compliant floors as a biomechanically effective strategy for reducing fall-related injuries including traumatic brain injuries and skull fractures.

Falling-incident detection and throughput enhancement in a multi-camera video-surveillance system - Corrected Proof

Wann-Yun Shieh, Ju-Chin Huang — 2011-12-12

Abstract: For most elderly, unpredictable falling incidents may occur at the corner of stairs or a long corridor due to body frailty. If we delay to rescue a falling elder who is likely fainting, more serious consequent injury may occur. Traditional secure or video surveillance systems need caregivers to monitor a centralized screen continuously, or need an elder to wear sensors to detect falling incidents, which explicitly waste much human power or cause inconvenience for elders. In this paper, we propose an automatic falling-detection algorithm and implement this algorithm in a multi-camera video surveillance system. The algorithm uses each camera to fetch the images from the regions required to be monitored. It then uses a falling-pattern recognition algorithm to determine if a falling incident has occurred. If yes, system will send short messages to someone needs to be noticed. The algorithm has been implemented in a DSP-based hardware acceleration board for functionality proof. Simulation results show that the accuracy of falling detection can achieve at least 90% and the throughput of a four-camera surveillance system can be improved by about 2.1 times.

Wireless instrumentation system based on dry electrodes for acquiring EEG signals - Corrected Proof

Nuno Sérgio Dias, João Paulo Carmo, Paulo Mateus Mendes, José Higino Correia — 2011-12-08

Abstract: This paper presents a complete non-invasive Wireless acquisition system based on dry electrodes for electroencephalograms (WiDE-EEG) with emphasis in the electronic system design. The WiDE-EEG is composed by a 2.4GHz radio-frequency (RF) transceiver, biopotential acquisition electronics and dry electrodes. The WiDE-EEG can acquire electroencephalogram (EEG) signals from 5 unipolar channels, with a resolution of 16bits and minimum analog amplitude of 9.98μVpp, at a sampling rate of 1000samples/s/channel and sends them to a processing unit through RF in a 10m range. The analog channels were optimized for EEG signals (with amplitudes in the range 70–100μV) and present the following characteristics: a signal gain of 66dB and a common mode rejection ratio of 56.5dB. Each electrode is composed by 16 microtip structures that were fabricated through bulk micromachining of a 〈100〉-type silicon substrate in a potassium hydroxide (KOH) solution. The microtips present solid angles of 54.7°, a height of 100–200μm and 2μm spaced apart. The electrodes have a thin layer (obtained by sputtering) of iridium oxide (IrO) to guaranty their biocompatibility and improve the contact with the skin. These dry electrodes are in direct contact with the electrolyte fluids of the inner skin layers, and avoid the use of conductive gels. The complete WiDE-EEG occupies a volume of 9cm×8.5cm×1cm, which makes it suitable for true mobility of the subjects and at the same time allows high data transfer rates. Since the WiDE-EEG is battery-powered, it overcomes the need of galvanic isolation for ensuring patient safety observed on conventional EEG instrumentation systems. The WiDE-EEG presents a total power consumption of 107mW, divided as follows: the acquisition system contributes with 10mW per channel, whereas the commercial MICAz module contributes with 57mW (e.g., 24mW from the microcontroller and 33mW from the RF chip). The WiDE-EEG also presents autonomy of about 25h with two class AA 1.5V batteries.

Rigid versus flexible plate fixation for periprosthetic femoral fracture—Computer modelling of a clinical case - Corrected Proof

2011-12-08

Abstract: A variety of plate designs have been implemented for treatment of periprosthetic femoral fracture (PFF) fixation. Controversy, however, exists with regard to optimum fixation methods using these plates. A clinical case of a PFF fixation (Vancouver type C) was studied where a rigid locking plate fixation was compared with a more flexible non-locking approach. A parametric computational model was developed in order to understand the underlying biomechanics between these two fixations. The model was used to estimate the overall stiffness and fracture movement of the two implemented methods. Further, the differing aspects of plate design and application were incrementally changed in four different models. The clinical case showed that a rigid fixation using a 4.5mm titanium locking plate with a short bridging length did not promote healing and ultimately failed. In contrast, a flexible fixation using 5.6mm stainless steel non-locking plate with a larger bridging length promoted healing. The computational results highlighted that changing the bridging length made a more substantial difference to the stiffness and fracture movement than varying other parameters. Further the computational model predicted the failure zone on the locking plate. In summary, rigid fracture fixation in the case of PFF can suppress the fracture movement to a degree that prevents healing and may ultimately fail. The computational approach demonstrated the potential of this technique to compare the stiffness and fracture movement of different fixation constructs in order to determine the optimum fixation method for PFF.

Feature selection from nocturnal oximetry using genetic algorithms to assist in obstructive sleep apnoea diagnosis - Corrected Proof

Daniel Álvarez, Roberto Hornero, J. Víctor Marcos, Félix del Campo — 2011-12-08

Abstract: Nocturnal pulse oximetry (NPO) has demonstrated to be a powerful tool to help in obstructive sleep apnoea (OSA) detection. However, additional analysis is needed to use NPO alone as an alternative to nocturnal polysomnography (NPSG), which is the gold standard for a definitive diagnosis. In the present study, we exhaustively analysed a database of blood oxygen saturation (SpO2) recordings (80 OSA-negative and 160 OSA-positive) to obtain further knowledge on the usefulness of NPO. Population set was randomly divided into training and test sets. A feature extraction stage was carried out: 16 features (time and frequency statistics and spectral and nonlinear features) were computed. A genetic algorithm (GA) approach was applied in the feature selection stage. Our methodology achieved 87.5% accuracy (90.6% sensitivity and 81.3% specificity) in the test set using a logistic regression (LR) classifier with a reduced number of complementary features (3 time domain statistics, 1 frequency domain statistic, 1 conventional spectral feature and 1 nonlinear feature) automatically selected by means of GAs. Our results improved diagnostic performance achieved with conventional oximetric indexes commonly used by physicians. We concluded that GAs could be an effective and robust tool to search for essential oximetric features that could enhance NPO in the context of OSA diagnosis.

Morphological characterization of cardiac induced intracranial pressure (ICP) waves in patients with overdrainage of cerebrospinal fluid and negative ICP - Corrected Proof

Per Kristian Eide, Marek Sroka, Aleksandra Wozniak, Terje Sæhle — 2011-12-08

Abstract: Symptomatic overdrainage of cerebrospinal fluid (CSF) can be seen in shunted hydrocephalus patients and in non-shunted patients with spontaneous intracranial hypotension (SIH). In these patients, intracranial pressure (ICP) monitoring often reveals negative static ICP, while it is less understood how the pulsatile ICP (cardiac induced ICP waves) is affected. This latter aspect is addressed in the present study. A set of 40 ICP recordings from paediatric and adult hydrocephalus patients were randomly selected. Each cardiac induced ICP wave was automatically identified and manually verified by the beginning and ending diastolic minimum pressures and the systolic maximum pressure. The ICP wave parameters (static pressure, amplitude, rise time, rise time coefficient, downward coefficient, wave duration, and area-under-curve) were then automatically computed. The material of 40 ICP recordings provided a total of 3,192,166 cardiac induced ICP waves (1,292,522 in paediatric patients and 1,899,644 in adult patients). No apparent changes in ICP wave parameters were seen when mean ICP became negative, except that the parameters amplitude, rise time coefficient, downward coefficient and area under curve somewhat increased when mean ICP was below −15mmHg.

LES of non-Newtonian physiological blood flow in a model of arterial stenosis - Corrected Proof

M.M. Molla, M.C. Paul — 2011-12-08

Abstract: Large Eddy Simulation (LES) is performed to study the physiological pulsatile transition-to-turbulent non-Newtonian blood flow through a 3D model of arterial stenosis by using five different blood viscosity models: (i) Power-law, (ii) Carreau, (iii) Quemada, (iv) Cross and (v) modified-Casson. The computational domain has been chosen is a simple channel with a biological type stenosis formed eccentrically on the top wall. The physiological pulsation is generated at the inlet of the model using the first four harmonic series of the physiological pressure pulse (Loudon and Tordesillas ). The effects of the various viscosity models are investigated in terms of the global maximum shear rate, post-stenotic re-circulation zone, mean shear stress, mean pressure, and turbulent kinetic energy. We find that the non-Newtonian viscosity models enlarge the length of the post-stenotic re-circulation region by moving the reattachment point of the shear layer separating from the upper wall further downstream. But the turbulent kinetic energy at the immediate post-lip of the stenosis drops due to the effects of the non-Newtonian viscosity. The importance of using LES in modelling the non-Newtonian physiological pulsatile blood flow is also assessed for the different viscosity models in terms of the results of the dynamic subgrid-scale (SGS) stress Smagorinsky model constant, Cs, and the corresponding SGS normalised viscosity.

Automated frequency domain analysis of oxygen saturation as a screening tool for SAHS - Corrected Proof

Daniel Sánchez Morillo, Nicole Gross, Antonio León, Luis F. Crespo — 2011-12-05

Abstract: Sleep apnea-hypopnea syndrome (SAHS) is significantly underdiagnosed and new screening systems are needed. The analysis of oxygen desaturation has been proposed as a screening method. However, when oxygen saturation (SpO2) is used as a standalone single channel device, algorithms working in time domain achieve either a high sensitivity or a high specificity, but not usually both. This limitation arises from the dependence of time-domain analysis on absolute SpO2 values and the lack of standardized thresholds defined as pathological.The aim of this study is to assess the degree of concordance between SAHS screening using offline frequency domain processing of SpO2 signals and the apnea-hypopnea index (AHI), and the diagnostic performance of such a new method. SpO2 signals from 115 subjects were analyzed. Data were divided in a training data set (37) and a test set (78). Power spectral density was calculated and related to the desaturation index scored by physicians. A frequency desaturation index (FDI) was then estimated and its accuracy compared to the classical desaturation index and to the apnea-hypopnea index. The findings point to a high diagnostic agreement: the best sensitivity and specificity values obtained were 83.33% and 80.44%, respectively. Moreover, the proposed method does not rely on absolute SpO2 values and is highly robust to artifacts.

Comparison of lead aVR “net QRS area” and “peak-to-peak amplitude” as indices of all limb electrocardiogram leads: Implications for the diagnosis, management, and follow-up in patients with heart failure - Corrected Proof

John E. Madias — 2011-12-05

Abstract: Nonreproducibility of precordial ECG leads in serial ECGs has led to emphasis on the limb leads. The sum of the “peak-to-peak amplitude” (Amp) of the QRS complexes of all 6 limb leads , has been employed as a metric in the follow-up of patients with edematous states (ES), including heart failure (HF). Since electrocardiographs measure leads I and II and calculate on line the remaining 4 limb leads, the sum of leads I and II (I+II), in any mathematical form, conceivably may reflect the corresponding variable of ∑6LbLds. In turn, due to the aVR=−(I+II)/2 relationship, aVR could be regarded as an index of ∑6LbLds. It is not known whether aVR “net QRS area”, i.e., positive minus negative QRS areas, has advantages over aVR Amp, as an index of ∑6LbLds. Automation-based measurements of Amps and “net QRS areas” of all 6 limb leads in 100 consecutive ECGs were analyzed, both employing and ignoring the algebraic signs (i.e., using the absolute or modulus, or |a| values), in the characterization of lead aVR or summations of metrics. There was an excellent correlation between “net QRS area” of aVR and I+II, between aVR and ∑6LbLds, and between I+II and ∑6LbLds (P=0.0005) when the algebraic signs were considered. There was an excellent correlation between the “net QRS area” of aVR and I+II, and between I+II and ∑6LbLds, but the correlation between aVR and ∑6LbLds (P=0.0005) was good, when the algebraic signs were ignored, and lower than when the algebraic signs were considered. Correlations between aVR or I+II, with ∑6LbLds were better when the Amp(s) than the “net QRS area(s) were considered. The QRS Amp aVR is better than the “net QRS area” aVR as an index of ∑6LbLds; however correlation of all the above ECG metrics with body weights and fluid balances in patients with ES and HF are needed to identify the optimal ECG metric(s) for clinical adoption.

Mechanically relevant consequences of the composite laminate-like design of the abdominal wall muscles and connective tissues - Corrected Proof

Stephen H.M. Brown — 2011-12-05

Abstract: Together, three abdominal wall muscles (external oblique, internal oblique and transversus abdominis) form a tightly bound muscular sheet that has been likened to a composite-laminate structure. Previous work has demonstrated the ability of force generated by these three muscles to be passed between one another through connective tissue linkages. Muscle fibres in each muscle are obliquely oriented with respect to its neighbouring muscles. It is proposed here is that this unique morphology of the abdominal wall muscles functions, through the application of constraining forces amongst the muscles, to increase force- and stiffness-generating capabilities. This paper presents a mathematical formulation of the stress–strain relationship for a transversely isotropic fibrous composite, and establishes a strengthening and stiffening effect when stress can be transferred between the fibrous layers. Application of empirical mechanical properties to this formulation demonstrates this effect for the abdominal wall muscles and, in greater proportion, for the anterior aponeurosis of the abdominal wall. This has implications for increasing the stiffness and passive load bearing ability of the abdominal wall muscles, and has the potential to modulate the whole muscle force–length and force–velocity relationships during contraction.

Fetal development, mechanobiology and optimal control processes can improve vascular tissue regeneration in bioreactors: An integrative review - Corrected Proof

Frédéric Couet, Sébastien Meghezi, Diego Mantovani — 2011-12-02

Abstract: Vascular tissue engineering aims to regenerate blood vessels to replace diseased arteries for cardiovascular patients. With the scaffold-based approach, cells are seeded on a scaffold showing specific properties and are expected to proliferate and self-organize into a functional vascular tissue. Bioreactors can significantly contribute to this objective by providing a suitable environment for the maturation of the tissue engineered blood vessel. It is recognized from the mechanotransduction principles that mechanical stimuli can influence the protein synthesis of the extra-cellular matrix thus leading to maturation and organization of the tissues. Up to date, no bioreactor is especially conceived to take advantage of the mechanobiology and optimize the construct maturation through an advanced control strategy. In this review, experimental strategies in the field of vascular tissue engineering are detailed, and a new approach inspired by fetal development, mechanobiology and optimal control paradigms is proposed. In this new approach, the culture conditions (i.e. flow, circumferential strain, pressure frequency, and others) are supposed to dynamically evolve to match the maturity of vascular constructs and maximize the efficiency of the regeneration process. Moreover, this approach allows the investigation of the mechanisms of growth, remodeling and mechanotransduction during the culture.

Wireless sensor networks for indoor air quality monitoring - Corrected Proof

2011-12-02

Abstract: The purpose of this study is to build an indoor air quality monitoring system based on wireless sensor networks (WSNs) technology. The main functions of the system include (1) remote parameter adjustment and firmware update mechanism for the sensors to enhance the flexibility and convenience of the system, (2) sensor nodes are designed by referring to the IEEE 1451.4 standard. This way, sensor nodes can automatically adjust and be plug and play, and (3) calibration method to strength the measurement value's sensitivity and accuracy. The experimental results show that transmission speed improves 30% than Trickle, transmission volume reduced to 42% of the original volume, updating task in 5*5 network topology can be executed 1.79 times and power consumption reduced to 30%. When baseline drifts, we can use the firmware update mechanism to adjust the reference value. The way can reduce error percentage from 15% to 7%.

Computer-assisted anatomically placed double-bundle ACL reconstruction: An in vitro experiment with different tension angles for the AM and the PL graft - Corrected Proof

J.W.H. Luites, A.B. Wymenga, L. Blankevoort, J.M.G. Kooloos, N. Verdonschot — 2011-12-02

Abstract: Anterior cruciate ligament reconstruction techniques are evolving with innovations like double-bundle (DB) grafts and computer assistance. The current DB techniques do not appear to make the clinical difference yet. Insight in various techniques may lead to better results. In this study, the anterior laxity of a DB reconstruction with an anteromedial (AM) graft fixated in 90° of flexion and a posterolateral (PL) graft fixated in 20° and computer-assisted anatomically placed femoral attachments was compared to normal values and single-bundle grafts. In 8 fresh-frozen human cadaveric knees, the anterior laxity was tested from 0° to 90° flexion, with a 100Newton (N) anterior tibial load in joints with (1) intact ACL, (2) torn ACL, (3) single-bundle (SB) graft tensed with 15N in 20°, (4) anatomic AM graft tensed with 15N in 90°, (5) anatomic PL graft tensed with 15N in 20°, and (6) anatomic DB graft (4+5).All reconstructions caused a posterior position of the tibia. Relative to the normal anterior laxity, the single-bundle techniques showed significantly increased laxities: The SB technique in 0° (+1.1mm) and 15° (+1.7mm); The AM reconstructions in 45° (+1.6mm) and 90° (+1.5mm); The PL reconstructions in all angles (from +1.4 to +2.3mm), except in 0°. The anatomic DB technique showed no significantly increased laxities and restored normal laxity in all angles.

Development of a foot scanner for assessing the mechanical properties of plantar soft tissues under different bodyweight loading in standing - Corrected Proof

Y.P. Zheng, Y.P. Huang, Y.P. Zhu, M. Wong, J.F. He, Z.M. Huang — 2011-12-02

Abstract: Mechanical properties of plantar soft tissues are important characteristics of the foot and are prone to being affected by foot pathologies such as diabetes. Therefore, it is of great importance to measure the mechanical properties of plantar soft tissues in vivo. However, such measurement in previous studies is mostly conducted in foot without loading and there is a paucity of instrument available which can assess the foot mechanical properties under a weight-loading status. In this study, a foot scanner incorporating a tissue ultrasound palpation (indentation) system (TUPS) which could assess the mechanical properties of plantar soft tissues under different body-weight loading was developed. The movement of the foot could also be monitored in real time during the indentation test to improve the test reliability. Preliminary tests were conducted on ten normal subjects at the heel region under various loading of the bodyweight. The results showed that the thickness decreased by 12.0% (from 13.83±2.52mm to 12.10±1.95mm) while the stiffness increased by 83.4% (from 40.0±20.7kPa to 69.0±26.0kPa) when the loading increased from 0% to 80% of the bodyweight (both p<0.001, repeated measure one-way ANOVA). Therefore, our system has been demonstrated to be useful in studying the loading dependence of mechanical properties of plantar soft tissues. Potential applications of the system in clinical studies for characterization and monitoring of foot pathologies such as ageing and diabetes are discussed at the end of this note.

Design and validation of a dynamic stretch splint for plantar fasciitis - Corrected Proof

Hsin-Yi Kathy Cheng, Yan-Ying Ju, Chun-Li Lin — 2011-11-28

Abstract: Background: Plantar fascia stretch plays an important role in the treatment of plantar fasciitis. Existing stretch splints mostly provide stretch to Achilles tendon but not to the plantar fascia. The ones that do are inefficient and uncomfortable because of their static nature. In this paper a dynamic stretch splint featured both ankle and metatarsophalangeal joint stretch was designed and developed. This splint should provide continuous stable stretch and be able to monitor the load of stretch during clinical application. To validate the design, twenty volunteers were tested under two stretch conditions, static and dynamic. Forces generated between the splint and the foot across 30-min testing were registered. Level of comfort and joint range-of-motion changes after splint application were evaluated. Statistical results demonstrated significant differences in load of stretch and in level of comfort between the static and dynamic conditions, but not in joint range-of-motion. The findings indicated that the designed splint could provide a continuous load of stretch, eliminate discomfort and increase user compliance comparing to static splint. Its long term effect onto joint angle improvement needs further investigation. Potentially it may be used on subjects with plantar fasciitis, and subjects with foot problems accompanying plantar tissue contracture.

A two-stage four-class BCI based on imaginary movements of the left and the right wrist - Corrected Proof

Aleksandra Vučković, Francisco Sepulveda — 2011-11-28

Abstract: This paper presents a new concept of a two-modality, four-class brain–computer interface (BCI) classifier based on motor imagination of the left and the right wrist. The noninvasive BCI combines classification of movements of the same limb (wrist flexion and extension) with classification of movements of different limbs, i.e., left and right wrist. Results were obtained from ten right-handed neurologically healthy volunteers. Subjects were not allowed to practice real movements before performing movement imagination. The mean classification accuracy for four different classes was 63±10%. Classification accuracy in four out of ten subjects was ≥70%. A two-stage four-class classifier showed significantly better classification results (p=0.014) than a single four-class classifier. Classifiers were based on Elman's neural networks and features were a selected set of absolute values of Gabor coefficients (GCs), calculated from the Independent Components, rather than the EEG signals’ time series. The most representative features for classification between movements of different limbs were in the alpha and the beta range, while for classification between movements of the same limb they were in the delta and the gamma range. There was no statistically significant difference between classification accuracy of movements of the right vs. the left wrist.

Numerical simulations of particle dynamics in a poststenotic blood vessel region within the scope of extracorporeal ultrasound stenosis treatment - Corrected Proof

M. Dhahbi, M. Ben Chiekh, B. Gilles, J.C. Béra, A. Jemni — 2011-11-28

Abstract: A numerical model was developed to predict the dynamics of a solid particle in a poststenotic blood vessel region. The flow through a 3D axisymmetric stenosis with 75% reduction in cross-section area was considered for inlet Reynolds numbers of 500 and 1000, which corresponds to typical values for the blood flow in human large arteries. Spherical particles were injected in the flow from the stenosis and tracked using the Discrete Phase Model (DPM) based on a Lagrangian approach. Within the scope of the development of ultrasound thrombolysis methods, the hydrodynamical forces predicted were used to evaluate the residence time of the particle and the minimal ultrasonic intensity required to keep it in the treatment region. For particle sizes larger than 400μm, the intensity required appeared to be compatible with extracorporeal therapeutic ultrasound.

Three-Dimensional Printing (3DP) of neonatal head phantom for ultrasound: Thermocouple embedding and simulation of bone - Corrected Proof

2011-11-21

Abstract: A neonatal head phantom, comprising of an ellipsoidal geometry and including a circular aperture for simulating the fontanel was designed and fabricated, in order to allow an objective assessment of thermal rise in tissues during trans-cranial ultrasonic scanning of pre-term neonates. The precise position of a series of thermocouples was determined on the basis of finite-element analysis, which identified crucial target points for the thermal monitoring within the phantom geometry. Three-Dimensional Printing (3DP) was employed for the manufacture of the skull phantom, which was subsequently filled with dedicated brain-mimic material. A novel 3DP material combination was found to be able to mimic the acoustic properties of neonatal skull bone. Similarly, variations of a standard recipe for tissue mimic were examined, until one was found to mimic the brain of an infant. A specific strategy was successfully pursued to embed a thermocouple within the 3DP skull phantom during the manufacturing process. An in-process machine vision system was used to assess the correct position of the deposited thermocouple inside the fabricated skull phantom. An external silicone-made skin-like covering completed the phantom and was manufactured through a Direct Rapid Tooling (DRT) technique.