Journal of Mechanics in Medicine and Biology

The prevention and diagnosis of cardiovascular diseases have become one of the primary problems in the medical community since the mortality of this kind of diseases accounts for 31% of global deaths in 2016. Heart sound, which is an important physiological signal of human body, mainly comes from the pulsing of cardiac structures and blood turbulence. The analysis of heart sounds plays an irreplaceable role in early diagnosis of heart disease since they contain a large amount of pathological information about each part of human heart. Heart sounds can be detected and recorded by Phonocardiogram (PCG). As a noninvasive method to detect and diagnose heart disease, PCG signals have been paid more and more attention by researchers. In this paper, a novel envelope extraction model is proposed and used to estimate the cardiac cycle of each PCG signal. We present a strategy combining empirical mode decomposition (EMD) technique and the proposed envelope model to extract the time-domain features. After applying EMD process to each PCG signal, the second intrinsic mode function is chosen for further analysis. Based on the proposed envelope model, the cardiac cycles of PCG signals can be estimated and then the time-domain features can be extracted. Combining with the frequency-domain features and wavelet-domain features, the feature vectors are obtained. Finally, the support vector machine (SVM) classifier is used to detect the normal and abnormal PCG signals. Two public datasets are used to test our framework in this paper. And classification accuracies of more than $96\%$ on both datasets show the effectiveness of the proposed model.

Head injuries in the vehicle crashes or pedestrian accidents can usually cause death or permanent disabilities, and head injuries resulting from the impact of car windshields remain a major problem. Anatomically, more realistic head models are required to more accurately document and evaluate the head-to-windshield impact responses and head injuries. The current study developed a head finite element model and carried out various simulations to investigate the head-to-windshield impact biomechanical responses and assess the head injuries. First, a 50th percentile three-dimensional finite element head model was developed and validated by using previously published cadaver experimental data. Then, the biomechanical responses were predicted under a head-to-windshield impact at different impact velocities (10, 12, and15m/s) and different inclination angles of the windshield (35^∘, 40^∘, and 45^∘). Finally, head injuries were investigated through examining various injury parameters. The results indicated that the contact force, the acceleration, the intracranial pressure, the deformation of the skull, and the negative pressure rose when the impact velocity and the inclination angles increased. Thus, the vehicle impact velocity and the inclination angle of the windshield greatly affect the severity of the resulting injuries on pedestrians’ heads, with the severity increasing with the impact velocity and windshield inclination angle.

Oxygen concentration plays a key role in cell survival and viability. Besides, it has important effects on essential cellular biological processes such as cell migration, differentiation, proliferation and apoptosis. Therefore, the prediction of the cellular response to the alterations of the oxygen concentration can help significantly in the advances of cell culture research. Here, we present a 3D computational mechanotactic model to simulate all the previously mentioned cell processes under different oxygen concentrations. With this model, three cases have been studied. Starting with mesenchymal stem cells within an extracellular matrix with mechanical properties suitable for its differentiation into osteoblasts, and under different oxygen conditions to evaluate their behavior under normoxia, hypoxia and anoxia. The obtained results, which are consistent with the experimental observations, indicate that cells tend to migrate toward zones with higher oxygen concentration where they accelerate their differentiation and proliferation. This technique can be employed to control cell migration toward fracture zones to accelerate the healing process. Besides, as expected, to avoid cell apoptosis under conditions of anoxia and to avoid the inhibition of the differentiation and proliferation processes under conditions of hypoxia, the state of normoxia should be maintained throughout the entire cell-culture process.

Glaucoma has emerged as the one of the leading causes of blindness. Even though the diagnosis of this disease has not yet been found, the early detection can cure the glaucoma disease. Various works presented for the glaucoma detection have many disadvantages such as increased run time, complex architecture, etc., during the real-time implementations. This work introduces the glaucoma detection system based on the proposed harmonic genetic-based support vector neural network (HG-SVNN) classifier. The proposed system detects glaucoma in the database through four major steps, (1) pre-processing, (2) proposed hybrid feature extraction, (3) segmentation and (4) classification through the proposed HG-SVNN classifier. The proposed model uses both the statistical and the vessel features from the segmented and the pre-processed images to construct the feature vector. The proposed HG-SVNN classifier uses both the harmonic operator and the genetic algorithm (GA) for the neural network training. From the simulation results, it is evident that the proposed glaucoma detection system has better performance than the existing works with the values of 0.945, 0.9, 0.9333 and 0.86667 for the segmentation accuracy, accuracy, sensitivity and specificity metric.

Postural stability assessments are typically used for training and tracking. The training results of stroke patients are investigated in terms of task execution and experimental methods. However, the selection of evaluation and training tools has not been discussed in depth. To explore the postural stability evaluation index, we used a range of widely applied assessment tools in occupational therapy. Methods: We studied the rehabilitation of 15 patients who had suffered chronic strokes for at least two years. The tools include the Timed Up and Go Test, which is used by rehabilitation professionals in postural stability evaluations, the biodex balance evaluation instrument, and a Kinect game developed for virtual reality therapy. Results: We propose an active and a passive assessment model. For training, we recommend combining active and passive assessments for confirmations. For assessments, the evaluation tool should be selected according to the postural stability task (active or passive). In the predictive models, if the different tools are considered simultaneously, static postural stability should be used as the main investigation. We suggest that by first studying the tools used to investigate postural stability assessments, balance assessments in stroke patients can also be improved.

Aortic dilation is associated with congenital bicuspid aortic valve (BAV) disease, and its etiology is still not completely understood. The aim of this study is to provide further insight into aortic hemodynamics in a BAV population with different degrees of aortic dilation and regurgitation in comparison with a patient without pathology. A fluid–structure interaction (FSI) numerical approach is implemented regarding patient-specific geometries, where the aortic valves are defined by analytical orifices. Results show that, while the patient without pathology displays a typical hemodynamic behavior of flows in bends, BAV-related aortas present an accelerated flow along the outer aortic wall. Wall shear stress (WSS) overload in the outer curvature is observed, more marked in more dilated aortas. Moreover, helices in the ascending aorta are present in these patients, enhanced with greater dilation. These findings support the fact that hemodynamic factors play an important role in aortic dilation onset and development in BAV patients, caused by a prolonged exposure of the outer ascending aortic curvature to altered WSS. Besides, our results suggest that greater aortic regurgitation may be associated with abnormal WSS distributions in the ascending aorta during diastole, which can facilitate aortic root dilation.

The behavior of the M. biceps femoris with regard to its enormous vulnerability to injuries in sport remains unclear. Despite prevention programs, the rate of injuries of the hamstring muscles has risen by more than 4% in recent years. To get more insights into its function, the aim of this study was to examine the effect of different muscle insertion characteristics and activation levels using a simulation. We created a multi-segmented muscle model for evaluating the critical behavior of M. biceps femoris during a one-legged stopping maneuver. We analyzed muscle function, movement of the knee angle after initial ground contact, the simulated muscle force and the stop torques in the knee joint. The insertion geometry has an elementary effect on knee joint function and contributes to knee extension. The muscle activity plays a decisive role in elementary muscle function regarding the knee joint and in this regard the internal load of the M. biceps femoris increased without showing any visible effects on the kinematics. The anthropometry and function of this muscle needs to be taken into account to assess its effects on injury risk.

Drilling through bone is one of the common cutting processes involved in many of the orthopedic surgeries. In bone drilling, spindle speed, feed rate, diameter of the drill bit, drill bit geometry and method of cooling are the important parameters to influence the in-situ temperature, drill thrust force and quality characteristics of the drilled hole. Because of the selection of inappropriate drilling parameters, uncontrolled large drilling forces, continuous increase in temperature and mechanical damage to the local host bone were observed. As these adverse effects lead to poor bone–implant contact and often a revision surgery, performing a surgical drilling with optimal parameters is essential to succeed in the surgical procedure. It was observed that in addition to the variations in apparent bone density, the orientation of osteons influences the drilling thrust force and temperature in bone drilling. Ten adult cadaveric human femurs from the age group of 32–65 years were considered and drilling experiments were conducted on proximal-diaphysis, mid-diaphysis and distal-diaphysis regions in the longitudinal, radial and circumferential directions. Bone drilling with different spindle speeds (500, 1000 and 1500rpm), feed rates (40, 60 and 80mm/min), and apparent density in the range of 0.98g/cm³ to 1.98g/cm³ was investigated in this work using a 3.20mm diameter surgical drill-bit. The generation of in-situ temperature as well as thrust force at each target location was measured using $T$-type thermocouple and Kistler${}^{\text{®}}$ dynamometer, respectively. Taguchi method based on membership function was used to optimize the drilling process. Then the efficacy of the method in reducing the in-situ temperature and thrust force, and quality of the drilled hole in respect of anatomical region and drilling direction was investigated using pull-out strength of the bone screws. Results revealed that the optimal parameters obtained from the Taguchi method based on membership function could simultaneously minimize the temperature as well as thrust force in bone drilling. The proposed method can be adopted to minimize the temperature and thrust force, and choose the best location nearest to the defect site for strong implant fixation by using CT datasets of the patient as the only input.

This work presents a developed zero-dimensional cardiovascular (CV) system model, based on an electrical analogy, with a detailed compartmental description of the heart and the main vascular circulation which is able to simulate normal and diseased conditions of CV system, especially the stenosis valvular aortic. To know the effect of each parameter on hemodynamics, the number of parameters is increased by adding more segments. The developed model consists of 14 compartments. The results show that the severity of aortic stenosis (AS) effect varies with the effective orifice area and the mean pressure gradient for the case of no AS; the effective orifice area is 4cm² and the mean pressure gradient is 0mmHg, while for the case of mild AS, the effective orifice area is 1.5cm² and the mean pressure gradient is 27.24mmHg. For the case of moderate AS, the effective orifice area is 1.0cm² and the mean pressure gradient is 44.68mmHg. For the case of the severe AS, the effective orifice area is 0.61cm² and the mean pressure gradient is 77.51mmHg. It is found that the developed model can estimate an accurate value of the effective orifice area for any value of mean pressure gradient in AS. The results obtained for the CV system under normal and diseased conditions show a good agreement compared to published results.

This study examined the effectiveness of floor markings for controlling cut width during the analysis of side cutting maneuvers. Eleven male basketball players performed two side cutting maneuvers of narrow (30cm) and wide (45cm) cut widths and were guided by floor markings. Ground reaction forces, together with ankle, knee, and hip joint ranges of motion (ROM), and respective joint moments were determined. Cut widths were verified by two approaches by calculating the actual foot-to-foot and foot-to-pelvis distances from motion data. Biomechanical lower extremity loading showed no significant differences in most kinetic and kinematic variables between narrow and wide cuts. The difference in foot-to-foot distance (15.1 [11.6, 18.7] cm, $p<0.001)$ between conditions corresponded well with floor markings, however, the difference in foot-to-pelvis distance was much smaller (2.3 [0.3, 4.4] cm, $p=0.030)$. It is concluded that floor markings are not sufficient for controlling the actual anatomical cut width in laboratory experiments. Participants may adjust their body postures to maintain similar lower extremity loading when performing side cuts differing in foot placement width. Cut width should be represented by foot-to-pelvis distance and not foot-to-foot distance.

Patients with lower extremity soft tissue sarcoma (STS) need to recover their walking ability while coping with lower-limb muscle loss due to tumor removal. However, the lack of information on walking after tumor removal hinders the development of gait rehabilitation strategies for such patients. The present study explored how patients walked after STS resection from the viewpoint of muscle forces. The effect of muscle removal and muscle strength asymmetry on estimated muscle forces was also investigated by iterating gait simulations for each patient using three different musculoskeletal models. These models differed based on whether or not the resected muscles were reflected in the model and whether or not residual muscle strength was scaled according to muscle strength measurements. Muscle forces during walking were estimated in six patients after thigh STS removal. Our results suggested that patients could walk using not only residual muscles that function similar to the resected muscles but also those that function differently (e.g., ankle plantarflexors). Gait simulations of patients with considerable muscle loss and those without a rectus femoris muscle were relatively sensitive to muscle removal.

Little is known about why and how biomechanics govern the hypothesis that three-Lag-Screw (3LS) fixation is a preferred therapeutic technique. A series models of surgical internal-fixation for femoral neck fractures of Pauwells-II will be constructed by an innovative approach of finite element so as to determine the most stable fixation by comparison of their biomechanical performance. Seventeen sets of CT scanned femora were imported onto Mimics extracting 3D models; these specimens were transferred to Geomagic Studio for a simulative osteotomy and kyrtograph; then, they underwent UG to fit simulative solid models; three sorts of internal fixators were expressed virtually by Pro-Engineer. Processed by Hypermesh, all compartments were assembled onto three systems actually as “Dynamic hip screw (DHS), 3LS and DHS+LS”. Eventually, numerical models of Finite Elemental Analysis (FEA) were exported to AnSys for solution. Three models for fixtures of Pauwells-II were established, validated and analyzed with the following findings: Femoral-shaft stress for $c$(3LS) is the least; Internal-fixator stress (MPa) for $a(\mathrm{\text{DHS}})=196.97>b(\mathrm{\text{DHS}}+\mathrm{\text{LS}})=88.37>c(3\mathrm{\text{LS}})=63.81$; Integral stress (MPa) for $a(\mathrm{\text{DHS}})=195.35>b(\mathrm{\text{DHS}}+\mathrm{\text{LS}})=86.72>c(3\mathrm{\text{LS}})=64.60$; displacement of femoral head (mm) for a$(\mathrm{\text{DHS}})=1.068>c(3\mathrm{\text{LS}})=1.010>b$(DHS+LS) = 0.735; displacement of femoral shaft (mm) for $c(3\mathrm{\text{LS}})=0.714>a(\mathrm{\text{DHS}})=0.533>b(\mathrm{\text{DHS+LS}})=0.475$; and displacement of fixators for $c(3\mathrm{\text{LS}})=0.982>a(\mathrm{\text{DHS}})=0.973>b(\mathrm{\text{DHS}}+\mathrm{\text{LS}})=0.706$. Mechanical comparisons for other femoral parks are insignificantly different, and these data can be abstracted as follows: the stress of 3LS-system was checked to be the least, and an interfragmentary displacement of DHS+LS assemblages was assessed to be the least”. A 3LS-system should be recommended to clinically optimize a Pauwells-II facture; if treated by this therapeutic fixation, breakage of fixators or secondary fracture is supposed to occur rarely. The strength of this study is that it was performed by a computer-aided simulation, allowing for design of a preoperative strategy that could provide acute correction and decrease procedure time, without harming to humans or animals.