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- Ahlström, Christer, 1977-, et al.
(författare)
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Noninvasive investigation of blood pressure changes using the pulse wave transit time : A novel approach in the monitoring of hemodialysis patients
- 2005
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Ingår i: Journal of Artificial Organs. - : Springer Science and Business Media LLC. - 1434-7229 .- 1619-0904. ; 8:3, s. 192-197
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Tidskriftsartikel (refereegranskat)abstract
- Severe blood pressure changes are well known in hemodialysis. Detection and prediction of these are important for the well-being of the patient and for optimizing treatment. New noninvasive methods for this purpose are required. The pulse wave transit time technique is an indirect estimation of blood pressure, and our intention is to investigate whether this technique is applicable for hemodialysis treatment. A measurement setup utilizing lower body negative pressure and isometric contraction was used to simulate dialysis-related blood pressure changes in normal test subjects. Systolic blood pressure levels were compared to different pulse wave transit times, including and excluding the cardiac preejection period. Based on the results of these investigations, a pulse wave transit time technique adapted for dialysis treatment was developed and tried out on patients. To determine systolic blood pressure in the normal group, the total pulse wave transit time was found most suitable (including the cardiac preejection period). Correlation coefficients were r = 0.80 ± 0.06 (mean ± SD) overall and r = 0.81 ± 0.16 and r = 0.09 ± 0.62 for the hypotension and hypertension phases, respectively. When applying the adapted technique in dialysis patients, large blood pressure variations could easily be detected when present. Pulse wave transit time is correlated to systolic blood pressure within the acceptable range for a trend-indicating system. The method's applicability for dialysis treatment requires further studies. The results indicate that large sudden pressure drops, like those seen in sudden hypovolemia, can be detected. © The Japanese Society for Artificial Organs 2005.
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- Johansson, Anders, 1972-
(författare)
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Biopolitics and Reflexivity : A Study of GMO Policymaking in the European Union
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The political discourse that has emerged as a consequence of establishing a European regulatory framework for GMOs has not been without problems. This dissertation addresses the political and regulatory challenges created by the development and use of genetically modified organisms (GMOs) in the EU. The underlying hypothesis in the dissertation is that the emergence of a European policy in the field of GMOs has appeared through new reflexive forms of governance. The aim of this research is to understand how these reflexive forms of regulation have emerged and operate within the EU, with a particular focus on the two GMO directives 90/220/EEC and 2001/18/EC. However, the study scrutinises the regulatory regimes from the 1970s onwards by investigating how the regulatory framework regarding GMOs has been developed and implemented in the EU. This is done through an analysis of the notion of ‘risk’ and the ‘precautionary principle’ since these concepts have been at the forefront of the GMO regulation debate. The empirical approach focuses on how the European Commission, the European Parliament and the European Council as well as other actors and institutions articulate ambivalence, interpretations and uncertainties in the decision-making processes regarding regulative measures for GMOs, with an accent on risk and the precautionary principle. The main empirical material has been documents concerning the inter-institutional process involved in the regulatory process of making the two directives. The analysis indicates that during the process of implementing GMO regulations, new steering strategies have appeared within the EU’s decision-making institutions when the objective of the regulation has taken centre stage in political and scientific controversies.
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- Johansson, Anders, 1972-, et al.
(författare)
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Estimation of respiratory volumes from the photoplethysmographic signal. Part 1 : experimental results
- 1999
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Ingår i: Medical and Biological Engineering and Computing. - 0140-0118 .- 1741-0444. ; 37:1, s. 42-47
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Tidskriftsartikel (refereegranskat)abstract
- To evaluate the possibility of respiratory-volume measurement using photoplethysmography (PPG), PPG signals from 16 normal volunteers are collected, and the respiratory-induced intensity variations (RIIV) are digitally extracted. The RIIV signals are studied while reepiratory volume is varied. Furthermore, respiratory rate, body posture and type of respiration are varied. A Fleisch pneumotachograph is used as the inspired volume reference. The RIIV and pneumotachography signals are compared, and a statisical analysis is performed (linear regression and t-tests). The key idea is that the amplitude of the RIIV signal is related to the respiratory volume. The conclusion from the measurements is that there exists a relationship between the amplitude of the RIIV signal and the respiratory volume (R=0.842, s=0.428, p<0.005). Absolute measurements of the respiratory volume are not possible from the RIIV signal with the present set-up. The RIIV signal also seems to be affected by respiratory rate and type. More knowledge about respiratory parameters and improved sensor and filter design are required to make absolute measurements of volumes possible.
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- Johansson, Anders, 1972-, et al.
(författare)
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Estimation of respiratory volumes from the photoplethysmographic signal. Part 2 : a model study
- 1999
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Ingår i: Medical and Biological Engineering and Computing. - 0140-0118 .- 1741-0444. ; 37:1, s. 48-53
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Tidskriftsartikel (refereegranskat)abstract
- A Windkessel model has been constructed with the aim of investigating the respiratory-volume dependence of the photoplethysmographic (PPG) signal. Experimental studies show a correlation between respiratory volume and the peak-to-peak value of the respiratory-induced intensity variations (RIIV) in the PPG signal. The model compartments are organised in two closed chambers, representing the thorax and the abdomen, and in a peripheral part not directly influenced by respiration. Cardiac pulse and respiration are created by continuous adjustment of the pressures in the affected compartments. Together with the criteria for heart and venous valves, the model is based on a set of 17 differential equations. These equations are solved for varying thoracic and abdominal pressures corresponding to different respiratory volumes. Furthermore, a sensitivity analysis is performed to evaluate the properties of the model. The PPG signals are created as a combination of peripheral blood flow and pressure. From these signals, the respiratory synchronous parts are extracted and analysed. To study some important limitations of the model, respiratory type and rate are varied. From the simulations, it is possible to verify our earlier experimental results concerning the relationship between respiratory volume and the peak-to-peak value of the RIIV signal. An expected decrease in the amplitude of the respiratory signal with increased respiratory rate is also found, which is due to the lowpass characteristics of the vessel system. Variations in the relationship between thoracic and abdominal respiration also affect the RIIV signal. The simulations explain and verify what has been found previously in experimental studies.
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