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| 2. |
- Broman, Mikael, et al.
(författare)
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Recirculation during veno-venous extra-corporeal membrane oxygenation - a simulation study
- 2015
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Ingår i: International Journal of Artificial Organs. - : SAGE Publications. - 0391-3988 .- 1724-6040. ; 38:1, s. 23-30
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Veno-venous ECMO is indicated in reversible life-threatening respiratory failure without life-threatening circulatory failure. Recirculation of oxygenated blood in the ECMO circuit decreases efficiency of patient oxygen delivery but is difficult to measure. We seek to identify and quantify some of the factors responsible for recirculation in a simulation model and compare with clinical data. Methods: A closed-loop real-time simulation model of the cardiovascular system has been developed. ECMO is simulated with a fixed flow pump 0 to 5 l/min with various cannulation sites -1) right atrium to inferior vena cava, 2) inferior vena cava to right atrium, and 3) superior+ inferior vena cava to right atrium. Simulations are compared to data from a retrospective cohort of 11 consecutive adult veno-venous ECMO patients in our department. Results: Recirculation increases with increasing ECMO-flow, decreases with increasing cardiac output, and is highly dependent on choice of cannulation sites. A more peripheral drainage site decreases recirculation substantially. Conclusions: Simulations suggest that recirculation is a significant clinical problem in veno-venous ECMO in agreement with clinical data. Due to the difficulties in measuring recirculation and interpretation of the venous oxygen saturation in the ECMO drainage blood, flow settings and cannula positioning should rather be optimized with help of arterial oxygenation parameters. Simulation may be useful in quantification and understanding of recirculation in VV-ECMO.
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| 3. |
- Härmark, Johan, et al.
(författare)
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Investigation of the elimination process of a multimodal polymer-shelled contrast agent in rats using ultrasound and transmission electron microscopy
- 2015
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Ingår i: Biomedical Spectroscopy and Imaging. - 2212-8794. ; 4:1, s. 81-93
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: A novel polymer-shelled contrast agent (CA) with multimodal imaging and target specific potential was developed recently and tested for its acoustical properties using different in-vitro setups.OBJECTIVE: The aim of this study was to investigate the elimination of three types of the novel polymer-shelled CA, one unmodified and two shell modified versions, in rats.METHODS: The blood elimination time was estimated by measuring the image intensity, from ultrasound images of the common carotid artery, over time after a bolus injection of the three types of the novel CA. The commercially available CA SonoVue was used as a reference. The subcellular localization of the three CAs was investigated using transmission electron microscopy.RESULTS: The ultrasound measurements indicated a blood half-life of 17–85 s for the different types of the novel CA, which was significant longer than the blood half-life time for SonoVue. Additionally, CAs were exclusively found in the circulatory system, either taken up by, or found in the vicinity of macrophages.CONCLUSIONS: Compared to the commercially available CA SonoVue, the blood circulation times for the three types of the novel polymer-shelled CA were prolonged. Moreover, macrophages were suggested to be responsible for the elimination of the CA.
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| 4. |
- Josefsson, Leila, et al.
(författare)
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Analysis of polyvinyl alcohol microbubbles in human blood plasma using capillary electrophoresis
- 2016
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Ingår i: Journal of Separation Science. - : Wiley-VCH Verlagsgesellschaft. - 1615-9306 .- 1615-9314. ; 39:8, s. 1551-1558
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Tidskriftsartikel (refereegranskat)abstract
- Recently, a new type of ultrasound contrast agent that consists of air-filled microbubbles stabilized with a shell of polyvinyl alcohol was developed. When superparamagnetic nanoparticles of iron oxide are incorporated in the polymer shell, a multimodal contrast agent can be obtained. The biodistribution and elimination pathways of the polyvinyl alcohol microbubbles are essential to investigate, which is limited with today's techniques. The aim of the present study was, therefore, to develop a method for qualitative and quantitative analysis of microbubbles in biological samples using capillary electrophoresis with ultraviolet detection. The analysis parameters were optimized to a wavelength at 260 nm and pH of the background electrolyte ranging between 11.9 and 12. Studies with high-intensity ultrasonication degraded microbubbles in water showed that degraded products and intact microbubbles could be distinguished, thus it was possible to quantify the intact microbubbles solely. Analysis of human blood plasma spiked with either plain microbubbles or microbubbles with nanoparticles demonstrated that it is possible to separate them from biological components like proteins in these kinds of samples.
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| 5. |
- Larsson, Malin K., et al.
(författare)
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The potential clinical value of contrast-enhanced echocardiography beyond current recommendations
- 2016
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Ingår i: Cardiovascular Ultrasound. - : BioMed Central. - 1476-7120. ; 14
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Tidskriftsartikel (refereegranskat)abstract
- Background: Contrast agents are used in resting echocardiography to opacify the left ventricular (LV) cavity and to improve LV endocardial border delineation in patients with suboptimal image quality. If a wider use of contrast-enhanced echocardiography would be adopted instead of the current selective approach, diagnoses such as myocardial ischemia and LV structural abnormalities could potentially be detected earlier. The aim was therefore to retrospectively investigate if contrast- enhanced echocardiography beyond the current recommendations for contrast agent usage affects assessment of wall motion abnormalities, ejection fraction (EF) and detection of LV structural abnormalities. A secondary aim was to evaluate the user dependency during image analysis. Methods: Experienced readers (n = 4) evaluated wall motion score index (WMSI) and measured EF on greyscale and contrast-enhanced images from 192 patients without indications for contrast-enhanced echocardiography. Additionally, screening for LV structural abnormalities was performed. Repeated measurements were performed in 20 patients by the experienced as well as by inexperienced (n = 2) readers. Results: Contrast analysis resulted in significantly higher WMSI compared to greyscale analysis (p < 0.003). Of the 83 patients, classified as healthy by greyscale analysis, 55 % were re-classified with motion abnormalities by contrast analysis. No significant difference in EF classification (>= 55 %, 45-54 %, 30-44 %, < 30 %) was observed. LV structural abnormalities, such as increased trabeculation (n = 21), apical aneurysm (n = 4), hypertrophy (n = 1) and thrombus (n = 1) were detected during contrast analysis. Intra- and interobserver variability for experienced readers as well as the variability between inexperienced and experienced readers decreased for WMSI and EF after contrast analysis. Conclusions: Contrast-enhanced echocardiography beyond current recommendations for contrast agent usage increased the number of detected wall motion and LV structural abnormalities. Moreover, contrast- enhanced echocardiography increased reproducibility for assessment of WMSI and EF.
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| 6. |
- Larsson, Malin, 1983-
(författare)
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Toward increased applicability of ultrasound contrast agents
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ultrasound is one of the most widely used modalities in medical imaging because of its high cost-effectiveness, wide availability in hospitals, generation of real-time images, and use of nonionizing radiation. However, the image quality can be insufficient in some patients. Introducing a contrast agent (CA), which comprises a suspension of 2–6 mm-sized microbubbles, improves the image quality and thus the image analysis. At present, contrast-enhanced ultrasound is frequently used during standard clinical procedures such as kidney, liver, and cardiac (echocardiography) imaging. Multimodality and targeted imaging are future areas for ultrasound CAs. Multimodality imaging may improve diagnostics by simultaneously providing anatomical and functional information. Targeted imaging may allow for identification of particular diseases.The work within this thesis focused mainly on a novel multimodal polymer-shelled CA with the potential to be target specific. In Study I, the acoustic response was determined in a flow phantom by evaluating the contrast-to-tissue-ratio when using contrast sequences available in clinical ultrasound systems. This study showed that a high acoustic pressure is needed for optimal visualization of the polymer-shelled CA. In Study II, the in vivo performance of this CA was evaluated in a rat model, and the blood elimination time and subcellular distribution were determined. In Study III, the efficiency in endocardial border delineation was assessed in a pig model. The polymer-shelled CA had a significantly longer blood circulation time than the commercially available CA SonoVue, which is favorable for target-specific CA, in which a long circulation time increases the probability of target-specific binding. Transmission electron microscopic analysis of tissue sections from liver, kidney, spleen and lungs, obtained at different time points after CA injection showed that macrophages were responsible for the elimination of the polymer-shelled CA. A higher dose of the polymer-shelled CA was needed to obtain similar endocardial border delineation efficiency as that obtained using SonoVue. The results of Studies I–III demonstrate that the polymer-shelled CA has potential applicability in medical imaging.Current guidelines for contrast-enhanced echocardiography are limited to cases of suboptimal image quality or when there is a suspicion of structural abnormalities within the left ventricle. It may be hypothesized that the wider use of contrast-enhanced echocardiography may help to detect some diseases earlier. Study IV assessed the diagnostic outcomes after contrast administration in patients without indications for CA use. The myocardial wall motion score index and ejection fraction were evaluated by experienced and inexperienced readers, and a screening for left ventricular structural abnormalities was performed. More cases of wall motion and structural abnormalities were detected in the contrast-enhanced analysis. Intra- and interobserver variability was lower with the use of CAs. This study suggests that the more widespread use of CAs instead of the current selective approach may contribute to earlier detection of cardiovascular disease.
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| 7. |
- Lindfors, M., et al.
(författare)
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Venous Cannula Positioning in Arterial Deoxygenation During Veno-Arterial Extracorporeal Membrane Oxygenation-A Simulation Study and Case Report
- 2016
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Ingår i: Artificial Organs. - : Wiley. - 0160-564X .- 1525-1594.
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Tidskriftsartikel (refereegranskat)abstract
- Venoarterial extracorporeal membrane oxygenation (VA-ECMO) is indicated in reversible life-threatening circulatory failure with or without respiratory failure. Arterial desaturation in the upper body is frequently seen in patients with peripheral arterial cannulation and severe respiratory failure. The importance of venous cannula positioning was explored in a computer simulation model and a clinical case was described. A closed-loop real-time simulation model has been developed including vascular segments, the heart with valves and pericardium. ECMO was simulated with a fixed flow pump and a selection of clinically relevant venous cannulation sites. A clinical case with no tidal volumes due to pneumonia and an arterial saturation of below 60% in the right hand despite VA-ECMO flow of 4 L/min was described. The case was compared with simulation data. Changing the venous cannulation site from the inferior to the superior caval vein increased arterial saturation in the right arm from below 60% to above 80% in the patient and from 64 to 81% in the simulation model without changing ECMO flow. The patient survived, was extubated and showed no signs of hypoxic damage. We conclude that venous drainage from the superior caval vein improves upper body arterial saturation during veno-arterial ECMO as compared with drainage solely from the inferior caval vein in patients with respiratory failure. The results from the simulation model are in agreement with the clinical scenario.
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| 8. |
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| 9. |
- Maksuti, Elira, et al.
(författare)
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ARTERIAL STIFFNESS ESTIMATION BY SHEAR WAVE ELASTOGRAPHY : VALIDATION IN PHANTOMS WITH MECHANICAL TESTING
- 2016
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Ingår i: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629 .- 1879-291X. ; 42:1, s. 308-321
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Tidskriftsartikel (refereegranskat)abstract
- Arterial stiffness is an independent risk factor found to correlate with a wide range of cardiovascular diseases. It has been suggested that shear wave elastography (SWE) can be used to quantitatively measure local arterial shear modulus, but an accuracy assessment of the technique for arterial applications has not yet been performed. In this study, the influence of confined geometry on shear modulus estimation, by both group and phase velocity analysis, was assessed, and the accuracy of SWE in comparison with mechanical testing was measured in nine pressurized arterial phantoms. The results indicated that group velocity with an infinite medium assumption estimated shear modulus values incorrectly in comparison with mechanical testing in arterial phantoms (6.7 +/- 0.0 kPa from group velocity and 30.5 +/- 0.4 kPa from mechanical testing). To the contrary, SWE measurements based on phase velocity analysis (30.6 +/- 3.2 kPa) were in good agreement with mechanical testing, with a relative error between the two techniques of 8.8 +/- 6.0% in the shear modulus range evaluated (40-100 kPa). SWE by phase velocity analysis was validated to accurately measure stiffness in arterial phantoms.
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| 10. |
- Maksuti, Elira, 1986-
(författare)
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Imaging and modeling the cardiovascular system
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Understanding cardiac pumping function is crucial to guiding diagnosis, predicting outcomes of interventions, and designing medical devices that interact with the cardiovascular system. Computer simulations of hemodynamics can show how the complex cardiovascular system is influenced by changes in single or multiple parameters and can be used to test clinical hypotheses. In addition, methods for the quantification of important markers such as elevated arterial stiffness would help reduce the morbidity and mortality related to cardiovascular disease.The general aim of this thesis work was to improve understanding of cardiovascular physiology and develop new methods for assisting clinicians during diagnosis and follow-up of treatment in cardiovascular disease. Both computer simulations and medical imaging were used to reach this goal.In the first study, a cardiac model based on piston-like motions of the atrioventricular plane was developed. In the second study, the presence of the anatomical basis needed to generate hydraulic forces during diastole was assessed in heathy volunteers. In the third study, a previously validated lumped-parameter model was used to quantify the contribution of arterial and cardiac changes to blood pressure during aging. In the fourth study, in-house software that measures arterial stiffness by ultrasound shear wave elastography (SWE) was developed and validated against mechanical testing.The studies showed that longitudinal movements of the atrioventricular plane can well explain cardiac pumping and that the macroscopic geometry of the heart enables the generation of hydraulic forces that aid ventricular filling. Additionally, simulations showed that structural changes in both the heart and the arterial system contribute to the progression of blood pressure with age. Finally, the SWE technique was validated to accurately measure stiffness in arterial phantoms.
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