| 1. |
- Ahlström, Christer, et al.
(författare)
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Feature Extraction for Systolic Heart Murmur Classification
- 2006
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Ingår i: Annals of Biomedical Engineering. - : Springer Science and Business Media LLC. - 0090-6964 .- 1573-9686. ; 34:11, s. 1666-1677
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Tidskriftsartikel (refereegranskat)abstract
- Heart murmurs are often the first signs of pathological changes of the heart valves, and they are usually found during auscultation in the primary health care. Distinguishing a pathological murmur from a physiological murmur is however difficult, why an “intelligent stethoscope” with decision support abilities would be of great value. Phonocardiographic signals were acquired from 36 patients with aortic valve stenosis, mitral insufficiency or physiological murmurs, and the data were analyzed with the aim to find a suitable feature subset for automatic classification of heart murmurs. Techniques such as Shannon energy, wavelets, fractal dimensions and recurrence quantification analysis were used to extract 207 features. 157 of these features have not previously been used in heart murmur classification. A multi-domain subset consisting of 14, both old and new, features was derived using Pudil’s sequential floating forward selection (SFFS) method. This subset was compared with several single domain feature sets. Using neural network classification, the selected multi-domain subset gave the best results; 86% correct classifications compared to 68% for the first runner-up. In conclusion, the derived feature set was superior to the comparative sets, and seems rather robust to noisy data.
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| 2. |
- Bergh, Niklas, 1979, et al.
(författare)
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A new biomechanical perfusion system for ex vivo study of small biological intact vessels
- 2005
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Ingår i: Ann Biomed Eng. - : Springer Science and Business Media LLC. - 0090-6964. ; 33:12, s. 1808-18
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Tidskriftsartikel (refereegranskat)abstract
- The vascular endothelium transduces physical stimuli within the circulation into physiological responses, which influence vascular remodelling and tissue homeostasis. Therefore, a new computerized biomechanical ex vivo perfusion system was developed, in which small intact vessels can be perfused under well-defined biomechanical forces. The system enables monitoring and regulation of vessel lumen diameter, shear stress, mean pressure, variable pulsatile pressure and flow profile, and diastolic reversal flow. Vessel lumen measuring technique is based on detection of the amount of flourescein over a vessel segment. A combination of flow resistances, on/off switches, and capacitances creates a wide range of pulsatile pressures and flow profiles. Accuracy of the diameter measurement was evaluated. The diameters of umbilical arteries were measured and compared with direct ultrasonographic measurement of the vessel diameter. As part of the validation the pulsatile pressure waveform was altered, e.g., in terms of pulse pressure, frequency, diastolic shape, and diastolic reversal flow. In a series of simulation experiments, the hemodynamic homeostasis functions of the system were successfully challenged by generating a wide range of vascular diameters in artificial and intact human vessels. We conclude that the system presented may serve as a methodological and technical platform when performing advanced hemodynamic stimulation protocols.
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| 3. |
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| 4. |
- Gasser, T. Christian, et al.
(författare)
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Modeling plaque fissuring and dissection during balloon angioplasty intervention
- 2007
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Ingår i: Annals of Biomedical Engineering. - : Springer Science and Business Media LLC. - 0090-6964 .- 1573-9686. ; 35:5, s. 711-723
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Tidskriftsartikel (refereegranskat)abstract
- Balloon angioplasty intervention is traumatic to arterial tissue. Fracture mechanisms such as plaque fissuring and/or dissection occur and constitute major contributions to the lumen enlargement. However, these types of mechanically-based traumatization of arterial tissue are also contributing factors to both acute procedural complications and chronic restenosis of the treatment site. We propose physical and finite element models, which are generally useable to trace fissuring and/or dissection in atherosclerotic plaques during balloon angioplasty interventions. The arterial wall is described as an anisotropic, heterogeneous, highly deformable, nearly incompressible body, whereas tissue failure is captured by a strong discontinuity kinematics and a novel cohesive zone model. The numerical implementation is based on the partition of unity finite element method and the interface element method. The later is used to link together meshes of the different tissue components. The balloon angioplasty-based failure mechanisms are numerically studied in 3D by means of an atherosclerotic-prone human external iliac artery, with a type V lesion. Image-based 3D geometry is generated and tissue-specific material properties are considered. Numerical results show that in a primary phase the plaque fissures at both shoulders of the fibrous cap and stops at the lamina elastica interna. In a secondary phase, local dissections between the intima and the media develop at the fibrous cap location with the smallest thickness. The predicted results indicate that plaque fissuring and dissection cause localized mechanical trauma, but prevent the main portion of the stenosis from high stress, and hence from continuous tissue damage.
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| 5. |
- Holzapfel, Gerhard A., et al.
(författare)
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Layer-specific 3D residual deformations of human aortas with non-atherosclerotic intimal thickening
- 2007
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Ingår i: Annals of Biomedical Engineering. - : Springer Science and Business Media LLC. - 0090-6964 .- 1573-9686. ; 35:4, s. 530-545
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Tidskriftsartikel (refereegranskat)abstract
- Data relating to residual deformations in human arteries are scarce. In this paper we investigate three-dimensional residual deformations for intact strips and for their separate layers from human aortas in their passive state. From 11 abdominal aortas with identified anamnesis, 16 pairs of rings and axial strips were harvested, and the rings cut open. After 16 h images of the resulting geometries were recorded, and the strips were separated into their three layers; after another 6 h images were again recorded. Image processing and analysis was then used to quantify residual stretches and curvatures. For each specimen histological analysis established that the intima, media and adventitia were clearly separated, and the separation was atraumatic. Axial in situ stretches were determined to be 1.196 +/- 0.084. On separation, the strips from the adventitia and media shortened (between 4.03 and 8.76% on average), while the intimal strips elongated on average by 3.84% (circumferential) and 4.28% (axial) relative to the associated intact strips. After separation, the adventitia from the ring sprang open by about 180 degrees on average, becoming flat, the intima opened only slightly, but the media sprang open by more than 180 degrees (as did the intact strip). The adventitia and intima from the axial strips remained flat, while the media (and the intact strip) bent away from the vessel axis. This study has shown that residual deformations are three dimensional and cannot be described by a single parameter such as 'the' opening angle. Their quantification and modeling therefore require consideration of both stretching and bending, which are highly layer-specific and axially dependent.
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| 6. |
- Jönsson, Björn, 1951-, et al.
(författare)
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A new probe for ankle systolic pressure measurement using Photoplethysmography (PPG)
- 2005
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Ingår i: Annals of Biomedical Engineering. - : Springer Science and Business Media LLC. - 0090-6964 .- 1573-9686. ; 33:2, s. 232-239
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Tidskriftsartikel (refereegranskat)abstract
- An automated method for ankle systolic pressure measurement, less operator dependent than the standard continuous wave (CW) Doppler technique, would imply an advantage both in patient measurements and in epidemiological studies. We present a new photoplethysmographic (PPG) probe that uses near-infrared light (880 nm) to detect pulsatory blood flow underneath the distal end of a standard pneumatic cuff. The probe is adapted to the anatomical conditions at the ankle, permitting recording of pressures in both ankle arteries separately. The validity of the equipment was tested with CW Doppler-derived systolic pressures and invasive blood pressure measurements for reference. In 20 healthy subjects, visual analysis of the PPG curves revealed a mean difference between CW Doppler and PPG measurements of –0.5 mmHg (SD 6.9). Corresponding results for the anterior and posterior tibial arteries separately were –1.8 mmHg (SD 6.2) and 0.9 mmHg (SD 7.3), respectively. A correct probe position was essential for the results. In direct recordings from the dorsalis pedis artery in 10 intensive care patients, PPG underestimated systolic pressure in the anterior tibial artery by 4.5 mmHg (SD 12.1). With further development, the PPG probe, integrated in the pneumatic cuff, may simplify measurements of ankle systolic pressures.
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| 7. |
- Kiousis, Dimitrios, et al.
(författare)
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A numerical model to study the interaction of vascular stents with human atherosclerotic lesions
- 2007
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Ingår i: Annals of Biomedical Engineering. - : Springer Science and Business Media LLC. - 0090-6964 .- 1573-9686. ; 35:11, s. 1857-1869
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Tidskriftsartikel (refereegranskat)abstract
- A methodology is proposed that identifies optimal stent devices for specific clinical criteria. It enables to predict the effect of stent designs on the mechanical environment of stenotic arteries. In particular, we present a numerical study which is based on the interaction of a vascular stent with a patient-specific, atherosclerotic human iliac lesion of type V. The stress evolution in four different tissue components during and after stenting is investigated. The geometric model of the artery is obtained through MRI, while anisotropic material models are applied to describe the behavior of tissues at finite strains. In order to model the observed fissuring and dissection of the plaque under dilation, the undeformed configuration of the arterial wall incorporates two initial tears. The 3D balloon-stent-artery interaction problem is modeled by means of a contact algorithm, which is based on a C-2-continuous surface parametrization, hence avoiding numerical instabilities of standard facet-based techniques. In the simulations three different stent designs are studied. The performance of each stent is characterized by scalar quantities relating to stress changes in the artery, contact forces, and changes in lumen area after stenting. The study concludes by suggesting two optimal stent designs for two different clinically relevant parameters.
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| 8. |
- Kiousis, D., et al.
(författare)
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Experimental Studies and Numerical Analysis of the Inflation and Interaction of Vascular Balloon Catheter-Stent Systems
- 2009
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Ingår i: Annals of Biomedical Engineering. - : Springer Science and Business Media LLC. - 0090-6964 .- 1573-9686. ; 37:2, s. 315-330
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Tidskriftsartikel (refereegranskat)abstract
- Balloon angioplasty with stenting is a well-established interventional procedure to treat stenotic arteries. Despite recent advances such as drug eluting stents, clinical studies suggest that stent design is linked to vascular injury. Additionally, dilation of the medical devices may trigger pathological responses such as growth and migration of vascular smooth cells, and may be a potent stimulus for neointimal hyperplasia. The purpose of this study is to experimentally investigate the mechanical characteristics of the transient expansion of six commercially available balloon-expandable stent systems, and to develop a robust finite element model based on the obtained experimental results. To reproduce the inflation of stent systems as in clinical practice, a pneumatic-hydraulic experimental setup is built, able to record loads and deformations. Characteristic pressure-diameter diagrams for the balloon-expandable stents and the detached balloons are experimentally obtained. Additionally, typical measures such as the burst opening pressure, the maximum dog-boning and foreshortening, and the elastic recoil are determined. The adopted constitutive models account for elastoplastic deformation of the stent, and for the nonlinear and anisotropic behavior of the balloon. The employed contact algorithm, based on a C (2)-continuous surface parametrization, efficiently simulates the interaction of the balloon and stent. The computational model is able to successfully capture the experimentally observed deformation mechanisms. Overall, the numerical results are in satisfactory agreement with experimental data.
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| 9. |
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| 10. |
- Overgaard, Rune V., et al.
(författare)
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Mathematical beta cell model for insulin secretion following IVGTT and OGTT
- 2006
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Ingår i: Annals of Biomedical Engineering. - : Springer Science and Business Media LLC. - 0090-6964 .- 1573-9686. ; 34:8, s. 1343-1354
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Tidskriftsartikel (refereegranskat)abstract
- Evaluation of beta cell function is conducted by a variety of glucose tolerance tests and evaluated by a number of different models with less than perfect consistency among results obtained from different tests. We formulated a new approximation of the distributed threshold model for insulin secretion in order to approach a model for quantifying beta cell function, not only for one, but for several different experiments. Data was obtained from 40 subjects that had both an oral glucose tolerance test (OGTT) and an intravenous tolerance test (IVGTT) performed. Parameter estimates from the two experimental protocols demonstrate similarity, reproducibility, and indications of prognostic relevance. Useful first phase indexes comprise the steady state amount of ready releasable insulin A(0) and the rate of redistribution k(rd), where both yield a considerable correlation (both r = 0.67) between IVGTT and OGTT estimates. For the IVGTT, A(0) correlates well (r = 0.96) with the 10 min area under the curve of insulin above baseline, whereas k(rd) represents a new and possibly more fundamental first phase index. For the useful second phase index gamma, a correlation of 0.75 was found between IVGTT and OGTT estimates.
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| 11. |
- Rodriguez, Jose F., et al.
(författare)
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The Effect of Material Model Formulation in the Stress Analysis of Abdominal Aortic Aneurysms
- 2009
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Ingår i: Annals of Biomedical Engineering. - : Springer Science and Business Media LLC. - 0090-6964 .- 1573-9686. ; 37:11, s. 2218-2221
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Tidskriftsartikel (refereegranskat)abstract
- A reliable estimation of wall stress in Abdominal Aortic Aneurysms (AAAs), requires performing an accurate three-dimensional reconstruction of the medical image-based native geometry and modeling an appropriate constitutive law for the aneurysmal tissue material characterization. A recent study on the biaxial mechanical behavior of human AAA tissue specimens demonstrates that aneurysmal tissue behaves mechanically anisotropic. Results shown in this communication show that the peak wall stress is highly sensitive to the anisotropic model used for the stress analysis. In addition, the present investigation indicates that structural parameters (e.g., collagen fiber orientation) should be determined independently and not by means of non-linear fitting to stress-strain test data. Fiber orientation identified in this manner could lead to overestimated peak wall stresses.
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| 12. |
- Song, Dan, et al.
(författare)
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Model-Based Sensorimotor Integration for Multi-Joint Control : Development of a Virtual Arm Model
- 2008
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Ingår i: Annals of Biomedical Engineering. - New York : Springer. - 0090-6964 .- 1573-9686. ; 36:6, s. 1033-1048
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Tidskriftsartikel (refereegranskat)abstract
- An integrated, sensorimotor virtual arm (VA) model has been developed and validated for simulation studies of control of human arm movements. Realistic anatomical features of shoulder, elbow and forearm joints were captured with a graphic modeling environment, SIMM. The model included 15 musculotendon elements acting at the shoulder, elbow and forearm. Muscle actions on joints were evaluated by SIMM generated moment arms that were matched to experimentally measured profiles. The Virtual Muscle (TM) (VM) model contained appropriate admixture of slow and fast twitch fibers with realistic physiological properties for force production. A realistic spindle model was embedded in each VM with inputs of fascicle length, gamma static (gamma(stat)) and dynamic (gamma(dyn)) controls and outputs of primary (I-a) and secondary (II) afferents. A piecewise linear model of Golgi Tendon Organ (GTO) represented the ensemble sampling (I-b) of the total muscle force at the tendon. All model components were integrated into a Simulink block using a special software tool. The complete VA model was validated with open-loop simulation at discrete hand positions within the full range of alpha and gamma drives to extrafusal and intrafusal muscle fibers. The model behaviors were consistent with a wide variety of physiological phenomena. Spindle afferents were effectively modulated by fusimotor drives and hand positions of the arm. These simulations validated the VA model as a computational tool for studying arm movement control. The VA model is available to researchers at website http://pt.usc.edu/cel.
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| 13. |
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