Current Issue : July - September Volume : 2014 Issue Number : 3 Articles : 5 Articles
Background: Computational simulation using numerical analysis methods can help\nto assess the complex biomechanical and functional characteristics of the mitral\nvalve (MV) apparatus. It is important to correctly determine physical contact\ninteraction between the MV apparatus components during computational MV\nevaluation. We hypothesize that leaflet-to-chordae contact interaction plays an\nimportant role in computational MV evaluation, specifically in quantitating the\ndegree of leaflet coaptation directly related to the severity of mitral regurgitation\n(MR). In this study, we have performed dynamic finite element simulations of MV\nfunction with and without leaflet-to-chordae contact interaction, and determined the\neffect of leaflet-to-chordae contact interaction on the computational MV evaluation.\nMethods: Computational virtual MV models were created using the MV geometric\ndata in a patient with normal MV without MR and another with pathologic MV with\nMR obtained from 3D echocardiography. Computational MV simulation with full\ncontact interaction was specified to incorporate entire physically available contact\ninteractions between the leaflets and chordae tendineae. Computational MV\nsimulation without leaflet-to-chordae contact interaction was specified by defining\nthe anterior and posterior leaflets as the only contact inclusion.\nResults: Without leaflet-to-chordae contact interaction, the computational MV\nsimulations demonstrated physically unrealistic contact interactions between the\nleaflets and chordae. With leaflet-to-chordae contact interaction, the anterior\nmarginal chordae retained the proper contact with the posterior leaflet during the\nentire systole. The size of the non-contact region in the simulation with leaflet-tochordae\ncontact interaction was much larger than for the simulation with only\nleaflet-to-leaflet contact.\nConclusions: We have successfully demonstrated the effect of leaflet-to-chordae\ncontact interaction on determining leaflet coaptation in computational dynamic MV\nevaluation. We found that physically realistic contact interactions between the leaflets\nand chordae should be considered to accurately quantitate leaflet coaptation for MV\nsimulation. Computational evaluation of MV function that allows precise quantitation\nof leaflet coaptation has great potential to better quantitate the severity of MR....
Electrochemotherapy is a local treatment of cancer employing electric pulses to\nimprove transmembrane transfer of cytotoxic drugs. In this paper we discuss\nelectrochemotherapy from the perspective of biomedical engineering and review\nthe steps needed to move such a treatment from initial prototypes into clinical\npractice. In the paper also basic theory of electrochemotherapy and preclinical studies\nin vitro and in vivo are briefly reviewed. Following this we present a short review of\nrecent clinical publications and discuss implementation of electrochemotherapy into\nstandard of care for treatment of skin tumors, and use of electrochemotherapy for\nother targets such as head and neck cancer, deep-seated tumors in the liver and\nintestinal tract, and brain metastases. Electrodes used in these specific cases are\npresented with their typical voltage amplitudes used in electrochemotherapy. Finally,\nkey points on what should be investigated in the future are presented and discussed....
Background: Atherosclerotic plaque progression and rupture are believed to be\nassociated with mechanical stress conditions. In this paper, patient-specific in vivo\nintravascular ultrasound (IVUS) coronary plaque image data were used to construct\ncomputational models with fluid-structure interaction (FSI) and cyclic bending to\ninvestigate correlations between plaque wall thickness and both flow shear stress\nand plaque wall stress conditions.\nMethods: IVUS data were acquired from 10 patients after voluntary informed\nconsent. The X-ray angiogram was obtained prior to the pullback of the IVUS catheter\nto determine the location of the coronary artery stenosis, vessel curvature and cardiac\nmotion. Cyclic bending was specified in the model representing the effect by heart\ncontraction. 3D anisotropic FSI models were constructed and solved to obtain flow\nshear stress (FSS) and plaque wall stress (PWS) values. FSS and PWS values were\nobtained for statistical analysis. Correlations with p < 0.05 were deemed significant.\nResults: Nine out of the 10 patients showed positive correlation between wall\nthickness and flow shear stress. The mean Pearson correlation r-value was 0.278 �± 0.181.\nSimilarly, 9 out of the 10 patients showed negative correlation between wall thickness\nand plaque wall stress. The mean Pearson correlation r-value was -0.530 �± 0.210.\nConclusion: Our results showed that plaque vessel wall thickness correlated positively\nwith FSS and negatively with PWS. The patient-specific IVUS-based modeling approach\nhas the potential to be used to investigate and identify possible mechanisms governing\nplaque progression and rupture and assist in diagnosis and intervention procedures.\nThis represents a new direction of research. Further investigations using more patient\nfollow-up data are warranted....
Background: The fatigue that users suffer when using steady-state visual evoked\npotential (SSVEP)-based brain-computer interfaces (BCIs) can cause a number of serious\nproblems such as signal quality degradation and system performance deterioration, usersâ��\ndiscomfort and even risk of photosensitive epileptic seizures, posing heavy restrictions on\nthe applications of SSVEP-based BCIs. Towards alleviating the fatigue, a fundamental step\nis to measure and evaluate it but most existing works adopt self-reported questionnaire\nmethods which are subjective, offline and memory dependent. This paper proposes an\nobjective and real-time approach based on electroencephalography (EEG) spectral\nanalysis to evaluate the fatigue in SSVEP-based BCIs.\nMethods: How the EEG indices (amplitudes in d, ?, a and �Ÿ frequency bands),\nthe selected ratio indices (?/a and (? + a)/�Ÿ), and SSVEP properties (amplitude\nand signal-to-noise ratio (SNR)) changes with the increasing fatigue level are\ninvestigated through two elaborate SSVEP-based BCI experiments, one validates\nmainly the effectiveness and another considers more practical situations. Meanwhile, a\nself-reported fatigue questionnaire is used to provide a subjective reference. ANOVA is\nemployed to test the significance of the difference between the alert state and the\nfatigue state for each index.\nResults: Consistent results are obtained in two experiments: the significant increases in\na and (? + a)/�Ÿ, as well as the decrease in ?/a are found associated with the increasing\nfatigue level, indicating that EEG spectral analysis can provide robust objective\nevaluation of the fatigue in SSVEP-based BCIs. Moreover, the results show that the\namplitude and SNR of the elicited SSVEP are significantly affected by usersâ�� fatigue.\nConclusions: The experiment results demonstrate the feasibility and effectiveness of\nthe proposed method as an objective and real-time evaluation of the fatigue in\nSSVEP-based BCIs. This method would be helpful in understanding the fatigue problem\nand optimizing the system design to alleviate the fatigue in SSVEP-based BCIs....
Background: Previous studies have consistently reported that decreasing seat height\nincreases the peak hip and knee joint moments; however, these findings may not\napply to biomechanical changes at very low seat heights. The purpose of this study,\ntherefore, was to examine the effect of a large range of seat heights on peak joint\nmoments of the lower limb during a sit-to-stand (STS) movement.\nMethods: Eight healthy young subjects participated in this experiment. Each subject\nwas instructed to stand up from six seat heights (10, 20, 30, 40, 50 and 60 cm). Joint\nmoments were calculated with an inverse dynamics method. The sum of the hip\nand knee joint moments was used as the index to indicate the mechanical load of\nthe STS movement. The effect of seat height on the mechanical load was examined\nwith both analytical and experimental approaches.\nResults: Through the analytical approach, it was revealed that the mechanical load\nof STS movements from low and normal seat heights (10 to 40 cm) always reaches\nits peak at or near the posture in which the thigh is horizontally positioned. This\nfinding indicates that the peak value is invariant between the low and normal seat\nheights. Similar results were also found in the experimental approach. There were\nfew significant differences in the peak mechanical load and the peak hip and knee\njoint moments between the low and normal seat heights, while they differed\nsignificantly between the low and high seat heights.\nConclusions: This study concluded that, while the peak mechanical load and the peak\nhip and knee joint moments increase inversely to seat height within the range of high\nto normal seat height (60 to 40 cm), they are invariant to the change of seat height\nwithin the range of low to normal seat height (10 to 40 cm). These findings are useful\nfor the design of chair, the improvement in the evaluation standard of minimum sit-tostand\nheight tests and the development of new muscular strength test....
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