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  • 1. Cacho, Fernando
    et al.
    Doblare, Manuel
    Holzapfel, Gerhard A.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Biomechanics.
    A procedure to simulate coronary artery bypass graft surgery2007In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 45, no 9, 819-827 p.Article in journal (Refereed)
    Abstract [en]

    In coronary artery bypass graft (CABG) surgery the involved tissues are overstretched, which may lead to intimal hyperplasia and graft failure. We propose a computational methodology for the simulation of traditional CABG surgery, and analyze the effect of two clinically relevant parameters on the artery and graft responses, i.e., incision length and insertion angle for a given graft diameter. The computational structural analyses are based on actual three-dimensional vessel dimensions of a human coronary artery and a human saphenous vein. The analyses consider the structure of the end-to-side anastomosis, the residual stresses and the typical anisotropic and nonlinear vessel behaviors. The coronary artery is modeled as a three-layer thick-walled tube. The finite element method is employed to predict deformation and stress distribution at various stages of CABG surgery. Small variations of the arterial incision have relatively big effects on the size of the arterial opening, which depends solely on the residual stress state. The incision length has a critical influence on the graft shape and the stress in the graft wall. Stresses at the heel region are higher than those at the toe region. The changes in the mechanical environment are severe along all transitions between the venous tissue and the host artery. Particular stress concentrations occur at the incision ends. The proposed computational methodology may be useful in designing a coronary anastomotic device for reducing surgical trauma. It may improve the quantitative knowledge of vessel diseases and serve as a tool for virtual planning of vascular surgery.

  • 2.
    Carlqvist, Håkan
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematics (Div.).
    Nikulin, Vadim V.
    Department of Clinical Neuroscience, Karolinska Institutet, Karolinska University Hospital, Stockholm.
    Strömberg, Jan-Olov
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematics (Div.).
    Brismar, T.
    Department of Clinical Neuroscience, Karolinska Institutet, Karolinska University Hospital, Stockholm.
    Amplitude and phase relationship between alpha and beta oscillations in the human electroencephalogram2005In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 43, no 5, 599-607 p.Article in journal (Refereed)
    Abstract [en]

    The relationship between the electro-encephalographic (EEG) alpha and beta oscillations in the resting condition was investigated in the study. EEGs were recorded in 33 subjects, and alpha (7.5-12.5Hz) and beta (15-25Hz) oscillations were extracted with the use of a modified wavelet transform. Power, peak frequency and phase synchronisation were evaluated for both types of oscillation. The average beta-alpha peak frequency ratio was about 1.9-2.0 for all electrode derivations. The peak frequency of beta activity was within 70-90 % of the 95 % confidence interval of twice the alpha frequency. A significant (p < 0.05) linear regression was found between beta and alpha power in all derivations in 32 subjects, with the slope of the regression line being approximate to 0.3. There was no significant difference in the slope of the line in different electrode locations, although the power correlation was strongest in the occipital locations where alpha and beta oscillations had the largest power. A significant 1:2 phase synchronisation was present between the alpha and beta oscillations, with a phase lag of about pi/2 in all electrode derivations. The strong frequency relationship between the resting beta and alpha oscillations suggests that they are generated by a common mechanism. Power and phase relationships were weaker suggesting that these properties can be modulated by additional mechanisms as well as be influenced by noise. A careful distinction between alpha-dependent and alpha-independent beta activity should be considered when making statements about the possible significance of genuine beta activity in different neurophysiological mechanisms.

  • 3.
    Eiken, Ola
    et al.
    Karolinska Institutet.
    Segerhammar, P.
    Elimination of breathing artefacts from impedance cardiograms at rest and during exercise1988In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 26, no 1, 13-16 p.Article in journal (Refereed)
  • 4. Jarverud, K.
    et al.
    Ollmar, Stig
    Brodin, Lars-Åke
    Analysis of the O-wave in acute right ventricular apex impedance measurements with a standard pacing lead in animals2002In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 40, no 5, 512-519 p.Article in journal (Refereed)
    Abstract [en]

    Modern pacemakers (implantable devices used for maintaining an appropriate heart rate in patients) can use an intracardiac ventricular impedance signal for physiological cardiac stimulation control. Intracardiac ventricular impedance from nine animal subjects is analysed and presented (seven sheep: 49.0 +/- 6.5 kg, sinus rhythm 100.3 +/- 16.5 beats min(-1), average impedance 629.8 +/- 72.6Omega; and two dogs: 30 kg each, sinus rhythm 86.0 beats min(-1), 862.1Omega and 134.0 beats min(-1), 1114.6Omega, respectively). The averaged curve and standard deviation curve of the impedance in sinus rhythm were analysed in MATLAB to clarify and study consistent impedance shape over one heart cycle. In eight of nine (89%) animal subjects, a consistent impedance slope change (notch) was observed in the early stage of the cardiac filling phase. This result was reproduced in an additional subject with simultaneous echocardiographical measurements of mitral valve blood flow. The notch occured soon after rapid early filling (E-wave in mitral flow) but prior to ventricular filling caused by atrial contraction, indicating that the impedance notch was caused by rapid ventricular filling and that it might be a sensed feature of diagnostic value. The intracardiac impedance notch in the present study had similar features to the non-invasive transthoracic impedance O-wave reported by others, and it is shown here that an O-wave is found in intracardiac impedance signals, strongly suggesting that the non-invasive O-wave is caused by cardiac events.

  • 5. Karlsson, M G D
    et al.
    Hübbert, L
    Lönn, U
    Janerot-Sjöberg, Birgitta
    KTH, School of Technology and Health (STH), Medical Engineering.
    Casimir-Ahn, H
    Wårdell, K
    Myocardial tissue motion influence on laser Doppler perfusion monitoring using tissue Doppler imaging.2004In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 42, no 6, 770-6 p.Article in journal (Refereed)
    Abstract [en]

    Tissue motion of the beating heart generates large movement artifacts in the laser Doppler perfusion monitoring (LDPM) signal. The aim of the study was to use tissue Doppler imaging (TDI) to localise intervals during the cardiac cycle where the influence of movement artifacts on the LDPM signal is minimum. TDI velocities and LDPM signals were investigated on three calves, for normal heartbeat and during occlusion of the left anterior descending coronary artery. Intervals of low tissue velocity (TDIint, < 1 cm s(-1)) during the cardiac cycle were identified. During occlusion, these intervals were compared with low LDPM signal intervals (LDPMint, <50% compared with baseline). Low-velocity intervals were found in late systole (normal and occlusion) and late diastole (normal). Systolic intervals were longer and less sensitive to heart rate variation compared with diastolic ones. The overlap between LDPMint and TDIint in relation to TDIint length was 84+/-27% (n = 14). The LDPM signal was significantly (p < 0.001, n = 14) lower during occlusion if calculated during minimum tissue motion (inside TDIint), compared with averaging over the entire cardiac cycle without taking tissue motion into consideration. In conclusion, movement artifacts are reduced if the LDPM signal is correlated to the ECG and investigated during minimum wall motion. The optimum interval depends on the application; late systole and late diastole can be used.

  • 6. Li, J.
    et al.
    Zhu, H. Y.
    He, Sailing
    Fast method for the localisation of current dipoles in the human brain2001In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 39, no 6, 678-680 p.Article in journal (Refereed)
  • 7. Nyström, J.
    et al.
    Lindholm-Sethson, B.
    Stenberg, L.
    Ollmar, Stig
    Eriksson, J. W.
    Geladi, P.
    Combined near-infrared spectroscopy and multifrequency bio-impedance investigation of skin alterations in diabetes patients based on multivariate analyses2003In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 41, no 3, 324-329 p.Article in journal (Refereed)
    Abstract [en]

    A group of 34 diabetic men, with different degrees of diabetes complications, including skin changes, were studied by near-infrared (NIR) spectroscopy and total body multi-frequency bio-impedance analyses (MFBIA-body). Skin reflectance spectra were measured with a fibre-optic probe in four locations (sites): hand, arm, leg and foot. As control subjects, a group of 23 healthy males were also measured. A combined multivariate analysis of the two types of spectrum was performed. It was concluded that the NIR method has the potential to detect diabetes-related skin conditions and also that the combination of the two techniques provides a higher potential for classification and discrimination of the skin conditions, with correct classification increasing from 63% to 85%.

  • 8. Strömberg, N O
    et al.
    Grönkvist, Mikael J.
    Swedish Defence Research Agency.
    Improved accuracy and extended flow range for a Fleisch pneumotachograph1999In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 37, no 4, 456-460 p.Article in journal (Refereed)
    Abstract [en]

    A large linear flow range and a small instrumental dead space volume are incompatible properties for a pneumotachometer (PTM). The linearity of a Fleisch number 2 PTM is studied for flows up to 6 litre s-1 (nominal range 0-2 litre s-1) with various up- and downstream geometries. It is hypothesised that using an array of calibration factors (conductance; flow/pressure), instead of a single calibration factor over the entire flow range, could improve accuracy and also extend the applicable flow range. The conductance against pressure characteristics are calculated with a previously described weighted averaging technique based on multiple strokes from a precision syringe. A single conductance value gives stroke volume errors in the range of -5 to 3% (0-2 litre s-1) and -6 to 11% (0-6 litre s-1) for validation using the same geometry as for calibration. The pressure dependent conductance improves accuracy to within -3% and 1% independent of flow range. However, for validation using a different geometry than for calibration, errors range from -5% to +8%. The degree of non-linearity varies between the geometries (range 3-15%) and is highest when using a one-directional valve upstream of the PTM and a Y-shaped connector. In conclusion, a pressure-dependent conductance improves accuracy and can also be used to extend the applicable flow range up to at least three times the nominal flow range.

  • 9. Tarjuelo-Gutierrez, J.
    et al.
    Rodriguez-Vila, B.
    Pierce, D. M.
    Fastl, T. E.
    Verbrugghe, P.
    Fourneau, I.
    Maleux, G.
    Herijgers, P.
    Holzapfel, Gerhard A.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Gomez, E. J.
    High-quality conforming hexahedral meshes of patient-specific abdominal aortic aneurysms including their intraluminal thrombi2014In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 52, no 2, 159-168 p.Article in journal (Refereed)
    Abstract [en]

    In order to perform finite element (FE) analyses of patient-specific abdominal aortic aneurysms, geometries derived from medical images must be meshed with suitable elements. We propose a semi-automatic method for generating conforming hexahedral meshes directly from contours segmented from medical images. Magnetic resonance images are generated using a protocol developed to give the abdominal aorta high contrast against the surrounding soft tissue. These data allow us to distinguish between the different structures of interest. We build novel quadrilateral meshes for each surface of the sectioned geometry and generate conforming hexahedral meshes by combining the quadrilateral meshes. The three-layered morphology of both the arterial wall and thrombus is incorporated using parameters determined from experiments. We demonstrate the quality of our patient-specific meshes using the element Scaled Jacobian. The method efficiently generates high-quality elements suitable for FE analysis, even in the bifurcation region of the aorta into the iliac arteries. For example, hexahedral meshes of up to 125,000 elements are generated in less than 130 s, with 94.8 % of elements well suited for FE analysis. We provide novel input for simulations by independently meshing both the arterial wall and intraluminal thrombus of the aneurysm, and their respective layered morphologies.

  • 10.
    Wiklund, Urban
    et al.
    Department of Biomedcal Engineering and Informatics, Univeristy Hospital of Umeå.
    Karlsson, Marcus
    Department of Biomedcal Engineering and Informatics, Univeristy Hospital of Umeå.
    Ostlund, Nils
    Department of Biomedcal Engineering and Informatics, Univeristy Hospital of Umeå.
    Berglin, Lena
    School of Textiles, University of Borås.
    Lindecrantz, Kaj
    School of Engineering, University of Borås.
    Karlsson, Stefan
    Engineering and Informatics, Univeristy Hospital of Umeå.
    Sandsjö, Leif
    National Institute of Working Life, Gothenburg.
    Adaptive spatio-temporal filtering of disturbed ECGs: a multi-channel approach to heartbeat detection in smart clothing2007In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 45, no 6, 515-523 p.Article in journal (Refereed)
    Abstract [en]

    Intermittent disturbances are common in ECG signals recorded with smart clothing: this is mainly because of displacement of the electrodes over the skin. We evaluated a novel adaptive method for spatio-temporal filtering for heartbeat detection in noisy multi-channel ECGs including short signal interruptions in single channels. Using multi-channel database recordings (12-channel ECGs from 10 healthy subjects), the results showed that multi-channel spatio-temporal filtering outperformed regular independent component analysis. We also recorded seven channels of ECG using a T-shirt with textile electrodes. Ten healthy subjects performed different sequences during a 10-min recording: resting, standing, flexing breast muscles, walking and pushups. Using adaptive multi-channel filtering, the sensitivity and precision was above 97% in nine subjects. Adaptive multi-channel spatio-temporal filtering can be used to detect heartbeats in ECGs with high noise levels. One application is heartbeat detection in noisy ECG recordings obtained by integrated textile electrodes in smart clothing.

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