| 1. |
- Ask, Jenny, 1976-, et al.
(författare)
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Terrestrial organic matter and light penetration : Effects on bacterial and primary production in lakes
- 2009
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Ingår i: Limnology and Oceanography. - : American Society of Limnology and Oceanography, Inc.. - 0024-3590 .- 1939-5590. ; 54:6, s. 2034-2040
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Tidskriftsartikel (refereegranskat)abstract
- We investigated productivity at the basal trophic level in 15 unproductive lakes in a gradient ranging from clear-water to brown-water (humic) lakes in northern Sweden. Primary production and bacterial production in benthic and pelagic habitats were measured to estimate the variation in energy mobilization from external energy sources (primary production plus bacterial production on allochthonous organic carbon) along the gradient. Clear-water lakes were dominated by autotrophic energy mobilization in the benthic habitat, whereas humic lakes were dominated by heterotrophic energy mobilization in the pelagic habitat. Whole-lake (benthic + pelagic) energy mobilization was negatively correlated to the light-extinction coefficient, which was determined by colored terrestrial organic matter in the lake water. Thus, variation in the concentration of terrestrial organic matter and its light-absorbing characteristics exerts strong control on the magnitude, as well as on the processes and pathways, of energy mobilization in unproductive lakes. We suggest that unproductive lakes in general are sensitive to input of terrestrial organic matter because of its effects on basal energy mobilization in both benthic and pelagic habitats.
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| 2. |
- Ask, Jenny, 1976-, et al.
(författare)
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Whole-lake estimates of carbon flux through algae and bacteria in benthic and pelagic habitats of clear-water lakes
- 2009
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Ingår i: Ecology. - Washington, DC, USA : Ecological Society of America. - 0012-9658 .- 1939-9170. ; 90:7, s. 1923-1932
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Tidskriftsartikel (refereegranskat)abstract
- This study quantified new biomass production of algae and bacteria in both benthic and pelagic habitats of clear-water lakes to contrast how carbon from the atmosphere and terrestrial sources regulates whole-lake metabolism. We studied four small unproductive lakes in subarctic northern Sweden during one summer season. The production of new biomass in both benthic and pelagic habitats was calculated as the sum of autotrophic production by algae and heterotrophic production by bacteria using allochthonous organic carbon (OC). Whole-lake production of new biomass was dominated by the benthic habitat (86% +/- 4% [mean +/- SD]) and by primary production (77% +/- 9%). Still, heterotrophic bacteria fueled by allochthonous OC constituted a significant portion of the new biomass production in both benthic (19% +/- 11%) and pelagic habitats (51% +/- 24%). In addition, overall net production (primary production minus respiration) was close to zero in the benthic habitats but highly negative (-163 +/- 81 mg C.m(-2).d(-1)) in pelagic regions of all lakes. We conclude (1) that allochthonous OC supported a significant part of total production of new biomass in both pelagic and benthic habitats, (2) that benthic habitats dominated the whole-lake production of new biomass, and (3) that respiration and net CO2 production dominated the carbon flux of the pelagic habitats and biomass production dominated the benthic carbon flux. Taken together, these findings suggest that previous investigations have greatly underestimated the productivity of clear-water lakes when benthic autotrophic production and metabolism of allochthonous OC have not been measured.
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| 3. |
- Ask, Per, 1978-, et al.
(författare)
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Competition mediated coexistence of invading intermediate consumer, ninespine stickleback, and a resident omnivorous top predator, Arctic char
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Climate change results in changes in the geographical distribution of species. Species invasion success into a new area is dependent both on the dispersal ability of species as well as the strength and identity of biotic interactions between resident and invading species. Coexistence in intraguild predation (IGP) systems depends on the relative strength of predation and competition interactions which in turn are temperature dependent. We investigated the effects of introducing an intermediate consumer, ninespine stickleback (Pungitius pungitius), into allopatric populations of the omnivorous top predator Arctic char (Salvelinus alpinus). Introductions were performed in lakes with different climate regimes, two tundra lakes and two forest lakes that differed in average summer temperatures with 1.4 ± 0.5 ºC (average ± 1SD). We found that sticklebacks were able to invade and increase in density in both tundra and forest lakes. Sticklebacks had strong negative effects on resource densities which also was reflected in a decreased growth of small char. Increasing stickleback density had a positive effect on growth of large adults and on the maximum size of char. We conclude that stickleback presence is not limited by biological interactions in these systems but rather by dispersion ability. We suggest that the size dependency in the response of char to the invasion of sticklebacks is fundamental for the successful invasion of sticklebacks, and that size dependent interactions including cannibalism play important roles for coexistence in natural IGP-systems.
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| 4. |
- Ask, Per, 1978-, et al.
(författare)
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Temperature mediated effects on top consumer populations in subarctic lakes
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The effects of temperature on top consumer populations in subarctic lake communities were studied by contrasting two lake pairs in different climate regimes: one pair on the low alpine tundra and one pair in the subalpine birch forest. We measured zooplankton and macroinvertebrate biomasses over the season and estimated population density and size structure of the top consumer Arctic char (Salvelinus alpinus). Furthermore, we modelled char growth using literature data on temperature dependent search rate, handling time and metabolic demands. The forest lakes were warmer than the tundra lakes. Char in the forest lakes were larger and had a higher individual growth compared to char in the tundra lakes, while population density and biomasses of char were not different between the forest and the tundra lakes. There were no differences in macroinvertebrate and zooplankton resource levels available for char between lake pairs. Our modeling of char growth revealed that higher temperature increased growth of char at the observed resource densities, suggesting that the higher temperature in the forest lakes was primarily the cause of the higher growth of char in these lakes. We suggest that cannibalism in char may regulate char recruitment and thereby population density and biomass of char leading to effects of increasing temperature on consumer biomass and consumer individual growth different from what is expected in pure consumer-resource systems. Our results emphasize the importance of feedbacks within ecosystems when addressing effects of climate change and increasing temperature on lake communities.
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| 5. |
- Hallberg, Per, 1965-
(författare)
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Applanation Resonance Tonometry for Intraocular Pressure Measurement
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Elevated intraocular pressure (IOP) is one of the major risk factors for glaucoma. Since glaucoma is a leading cause of blindness, reliable methods for measuring the IOP are important. This doctoral dissertation presents a new method, applanation resonance tonometry (ART), for measurement of IOP. The method is based on resonance sensor technology combined with the novel multipoint analysis of continuously sampled data of both contact force and contact area. The ART was evaluated in in vitro porcine-eye studies as well as in clinic on both healthy volunteers and patients. A new symmetric probe with a larger sensor tip and improved aligning light was developed and evaluated in vitro. It showed that the error from off-centring was highly reduced. The new ART probe, used as a biomicroscope device (ARTBiom) and as a handheld device (ARTHand), was further evaluated in a clinical study designed in accordance with the International Standard Organisation’s (ISO) requirement. Both the ARTBiom and the ARTHand met the precision set by the requirements. Laser surgery is a common way to correct vision. The biomechanical effect of photorefractive keratectomy (PRK) on IOP measurements was evaluated using Goldmann applanation tonometry (GAT) and ART in an in vitro study. Both methods were affected, but to a different extent. The flat contact probe of GAT, as compared with the convex tip of ART, and single point vs. multipoint approach, provide explanation to the ART advantage regarding measurement error of IOP after PRK. In conclusion, resonance sensor technology has made it possible to introduce a new multipoint method for measuring IOP, and the method is relevant for measuring IOP in humans. It may be possible to reduce errors in the clinical measurement of IOP with this new method, especially after corneal surgery. The ART has the potential to become a useful clinical instrument for IOP measurement.
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| 6. |
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| 7. |
- Karlsson, Jan, et al.
(författare)
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Light limitation of nutrient-poor lake ecosystems
- 2009
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 460, s. 506-509
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Tidskriftsartikel (refereegranskat)abstract
- Productivity denotes the rate of biomass synthesis in ecosystems and is a fundamental characteristic that frames ecosystem function and management. Limitation of productivity by nutrient availability is an established paradigm for lake ecosystems1, 2, 3. Here, we assess the relevance of this paradigm for a majority of the world's small, nutrient-poor lakes, with different concentrations of coloured organic matter4, 5. By comparing small unproductive lakes along a water colour gradient, we show that coloured terrestrial organic matter controls the key process for new biomass synthesis (the benthic primary production) through its effects on light attenuation. We also show that this translates into effects on production and biomass of higher trophic levels (benthic invertebrates and fish). These results are inconsistent with the idea that nutrient supply primarily controls lake productivity, and we propose that a large share of the world's unproductive lakes, within natural variations of organic carbon and nutrient input, are limited by light and not by nutrients. We anticipate that our result will have implications for understanding lake ecosystem function and responses to environmental change. Catchment export of coloured organic matter is sensitive to short-term natural variability and long-term, large-scale changes, driven by climate and different anthropogenic influences6, 7. Consequently, changes in terrestrial carbon cycling will have pronounced effects on most lake ecosystems by mediating changes in light climate and productivity of lakes.
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| 8. |
- Nyqvist, Johanna, et al.
(författare)
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Differences in health related quality of life in the randomised ARTSCAN study; accelerated vs. conventional radiotherapy for head and neck cancer. A five year follow up
- 2016
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Ingår i: Radiotherapy and Oncology. - : Elsevier BV. - 0167-8140 .- 1879-0887. ; 118:2, s. 335-341
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Tidskriftsartikel (refereegranskat)abstract
- Background and purpose: Health related quality of life (HRQoL) was assessed in the randomised, prospective ARTSCAN study comparing conventional radiotherapy (CF) with accelerated radiotherapy (AF) for head and neck cancer. Material and methods: 750 patients with squamous cell carcinoma (of any grade and stage) in the oral cavity, oro-, or hypopharynx or larynx (except T1-2, NO glottic carcinoma) without distant metastases were randomised to either conventional fractionation (2 Gy/day, 5 days/week in 49 days, total dose 68 Gy) or accelerated fractionation (1.1 + 2.0 Gy/day, 5 days/week in 35 days, total dose 68 Gy). HRQoL was assessed with EORTC QLQ-C30, QLQ-H&N35 and HADS at baseline, at end of radiotherapy (eRT) and at 3 and 6 months and 1, 2 and 5 years after start of treatment. Results: The AF group reported HRQoL was significantly lower at eRT and at 3 months for most symptoms, scales and functions. Few significant differences were noted between the groups at 6 months and 5 years. Scores related to functional oral intake never reached baseline. Conclusion: In comparison to CF, AF has a stronger adverse effect on HRQoL in the acute phase.
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| 9. |
- Xiong, Changsheng, et al.
(författare)
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Problems in timing of respiration with the nasal thermistor technique.
- 1993
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Ingår i: Journal of the American Society of Echocardiography. - 0894-7317 .- 1097-6795. ; 6:2, s. 210-216
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Tidskriftsartikel (refereegranskat)abstract
- When one analyzes transvalvular and venous flow velocity patterns, it is important to relate them to respiration. For this reason a nasal thermistor technique is often used, although it is known that this signal is delayed in relation to intrathoracic pressure changes. The magnitude and variation in delay have not been investigated previously and were, therefore, studied in a model experiment in 10 normal subjects, in 10 patients with obstructive, and in 10 patients with restrictive pulmonary disease. Esophageal pressure variations measured with an air-filled balloon served as a gold standard for intrathoracic pressure changes. During basal conditions there was, for both patient groups and normal subjects, a considerable delay of the thermistor signal. The average delay for all subjects was 370 msec with a wide variation (from 120 to 720 msec). At higher breathing frequencies the delay shortened to 310 msec (P < 0.01) but there was still a wide variation (ranging from 200 to 470 msec). Theoretic calculations show that the delay caused by the respiratory system accounts for only a minor portion of the total delay. Model experiments confirmed that the response characteristics of the thermistor probes limit the accuracy in timing of respiration. The total delay with the investigated thermistor technique is too long and variable to fulfil clinical demands.
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| 10. |
- Ahlström, Christer, et al.
(författare)
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A method for accurate localization of the first heart sound and possible applications
- 2008
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Ingår i: Physiological Measurement. - : Institutionen för medicinsk teknik. - 0967-3334 .- 1361-6579. ; 29:3, s. 417-428
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Tidskriftsartikel (refereegranskat)abstract
- We have previously developed a method for localization of the first heart sound (S1) using wavelet denoising and ECG-gated peak-picking. In this study, an additional enhancement step based on cross-correlation and ECG-gated ensemble averaging (EA) is presented. The main objective of the improved method was to localize S1 with very high temporal accuracy in (pseudo-) real time. The performance of S1 detection and localization, with and without EA enhancement, was evaluated on simulated as well as experimental data. The simulation study showed that EA enhancement reduced the localization error considerably and that S1 could be accurately localized at much lower signal-to-noise ratios. The experimental data were taken from ten healthy subjects at rest and during invoked hyper- and hypotension. For this material, the number of correct S1 detections increased from 91% to 98% when using EA enhancement. Improved performance was also demonstrated when EA enhancement was used for continuous tracking of blood pressure changes and for respiration monitoring via the electromechanical activation time. These are two typical applications where accurate localization of S1 is essential for the results.
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| 11. |
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| 12. |
- Ahlström, Christer, et al.
(författare)
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Assessing Aortic Stenosis using Sample Entropy of the Phonocardiographic Signal in Dogs
- 2008
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Ingår i: IEEE Transactions on Biomedical Engineering. - 0018-9294 .- 1558-2531. ; 55:8, s. 2107-2109
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Tidskriftsartikel (refereegranskat)abstract
- In aortic valve stenosis (AS), heart murmurs arise as an effect of turbulent blood flow distal to the obstructed valves. With increasing AS severity, the flow becomes more unstable, and the ensuing murmur becomes more complex. We hypothesize that these hemodynamic flow changes can be quantified based on the complexity of the phonocardiographic (PCG) signal. In this study, sample entropy (SampEn) was investigated as a measure of complexity using a dog model. Twenty-seven boxer dogs with various degrees of AS were examined with Doppler echocardiography, and the peak aortic flow velocity (Vmax) was used as a reference of AS severity. SampEn correlated to Vmax with R = 0.70 using logarithmic regression. In a separate analysis, significant differences were found between physiologic murmurs and murmurs caused by AS (p < 0.05), and the area under a receiver operating characteristic curve was calculated to 0.96. Comparison with previously presented PCG measures for AS assessment showed improved performance when using SampEn, especially for differentiation between physiological murmurs and murmurs caused by mild AS. Studies in patients will be needed to properly assess the technique in humans.
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| 13. |
- Ahlström, Christer, 1977-, et al.
(författare)
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Assessment of Suspected Aortic Stenosis by Auto Mutual Information Analysis of Murmurs
- 2007
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Ingår i: Engineering in Medicine and Biology Society, 2007. EMBS 2007. - 9781424407873 ; , s. 1945-1948
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Konferensbidrag (refereegranskat)abstract
- Mild sclerotic thickening of the aortic valve affects 25% of the population, and the condition causes aortic valve stenosis (AS) in 2% of adults above 65 years. Echocardiography is today the clinical standard for assessing AS. However, a cost effective and uncomplicated technique that can be used for decision support in the primary health care would be of great value. In this study, recorded phonocardiographic signals were analyzed using the first local minimum of the auto mutual information (AMI) function. The AMI method measures the complexity in the sound signal, which is related to the amount of turbulence in the blood flow and thus to the severity of the stenosis. Two previously developed phonocardiographic methods for assessing AS severity were used for comparison, the murmur energy ratio and the sound spectral averaging technique. Twenty-nine patients with suspected AS were examined with Doppler echocardiography. The aortic jet velocity was used as a reference of AS severity, and it was found to correlate with the AMI method, the murmur energy ratio and the sound spectral averaging technique with the correlation coefficient R = 0.82, R = 0.73 and R = 0.76, respectively.
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| 14. |
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| 15. |
- Ahlström, Christer, et al.
(författare)
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Chaotic dynamics of respiratory sounds
- 2006
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Ingår i: Chaos, Solitons & Fractals. - : Elsevier BV. - 0960-0779 .- 1873-2887. ; 29:5, s. 1054-1062
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Tidskriftsartikel (refereegranskat)abstract
- There is a growing interest in nonlinear analysis of respiratory sounds (RS), but little has been done to justify the use of nonlinear tools on such data. The aim of this paper is to investigate the stationarity, linearity and chaotic dynamics of recorded RS. Two independent data sets from 8 + 8 healthy subjects were recorded and investigated. The first set consisted of lung sounds (LS) recorded with an electronic stethoscope and the other of tracheal sounds (TS) recorded with a contact accelerometer. Recurrence plot analysis revealed that both LS and TS are quasistationary, with the parts corresponding to inspiratory and expiratory flow plateaus being stationary. Surrogate data tests could not provide statistically sufficient evidence regarding the nonlinearity of the data. The null hypothesis could not be rejected in 4 out of 32 LS cases and in 15 out of 32 TS cases. However, the Lyapunov spectra, the correlation dimension (D2) and the Kaplan-Yorke dimension (DKY) all indicate chaotic behavior. The Lyapunov analysis showed that the sum of the exponents was negative in all cases and that the largest exponent was found to be positive. The results are partly ambiguous, but provide some evidence of chaotic dynamics of RS, both concerning LS and TS. The results motivate continuous use of nonlinear tools for analysing RS data. © 2005 Elsevier Ltd. All rights reserved.
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| 16. |
- Ahlström, Christer, et al.
(författare)
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Detection of the 3rd Heart Sound using Recurrence Time Statistics
- 2006
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Ingår i: Proc. 31st IEEE Int. Conf. on Acoustics, Speech and Signal Processing, Toulouse, France, 2006. - 9781424404681 ; , s. 1040-1043
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The 3rd heart sound (S3) is normally heard during auscultation of younger individuals, but it is also common in many patients with heart failure. Compared to the 1st and 2nd heart sounds, S3 has low amplitude and low frequency content, making it hard to detect (both manually for the physician and automatically by a detection algorithm). We present an algorithm based on a recurrence time statistic which is sensitive to changes in a reconstructed state space, particularly for detection of transitions with very low energy. Heart sound signals from ten children were used in this study. Most S3 occurrences were detected (98 %), but the amount of false extra detections was rather high (7% of the heart cycles). In conclusion, the method seems capable of detecting S3 with high accuracy and robustness.
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| 17. |
- Ahlström, Christer, 1977-, et al.
(författare)
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Distinguishing Innocent Murmurs from Murmurs caused by Aortic Stenosis by Recurrence Quantification Analysis
- 2006
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Ingår i: ROCEEDINGS OF WORLD ACADEMY OF SCIENCE, ENGINEERING AND TECHNOLOGY, VOL 18. - Canakkale, Turkey : World Academy of Science, Engineering and Technology (W A S E T). ; , s. 40-45
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Konferensbidrag (refereegranskat)abstract
- It is sometimes difficult to differentiate between innocent murmurs and pathological murmurs during auscultation. In these difficult cases, an intelligent stethoscope with decision support abilities would be of great value. In this study, using a dog model, phonocardiographic recordings were obtained from 27 boxer dogs with various degrees of aortic stenosis (AS) severity. As a reference for severity assessment, continuous wave Doppler was used. The data were analyzed with recurrence quantification analysis (RQA) with the aim to find features able to distinguish innocent murmurs from murmurs caused by AS. Four out of eight investigated RQA features showed significant differences between innocent murmurs and pathological murmurs. Using a plain linear discriminant analysis classifier, the best pair of features (recurrence rate and entropy) resulted in a sensitivity of 90% and a specificity of 88%. In conclusion, RQA provide valid features which can be used for differentiation between innocent murmurs and murmurs caused by AS.
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| 18. |
- 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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| 19. |
- Ahlström, Christer, et al.
(författare)
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Heart sound cancellation from lung sound recordings using recurrence time statistics and nonlinear prediction
- 2005
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Ingår i: IEEE Signal Processing Letters. - : Institutionen för medicinsk teknik. - 1070-9908 .- 1558-2361. ; 12:12, s. 812-815, s. 812-815
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Tidskriftsartikel (refereegranskat)abstract
- Heart sounds (HS) obscure the interpretation of lung sounds (LS). This letter presents a new method to detect and remove this undesired disturbance. The HS detection algorithm is based on a recurrence time statistic that is sensitive to changes in a reconstructed state space. Signal segments that are found to contain HS are removed, and the arising missing parts are replaced with predicted LS using a nonlinear prediction scheme. The prediction operates in the reconstructed state space and uses an iterated integrated nearest trajectory algorithm. The HS detection algorithm detects HS with an error rate of 4% false positives and 8% false negatives. The spectral difference between the reconstructed LS signal and an LS signal with removed HS was 0.34/spl plusmn/0.25, 0.50/spl plusmn/0.33, 0.46/spl plusmn/0.35, and 0.94/spl plusmn/0.64 dB/Hz in the frequency bands 20-40, 40-70, 70-150, and 150-300 Hz, respectively. The cross-correlation index was found to be 99.7%, indicating excellent similarity between actual LS and predicted LS. Listening tests performed by a skilled physician showed high-quality auditory results.
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| 20. |
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| 21. |
- 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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| 22. |
- Ahlström, Christer, 1977-
(författare)
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Nonlinear phonocardiographic Signal Processing
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis work has been to develop signal analysis methods for a computerized cardiac auscultation system, the intelligent stethoscope. In particular, the work focuses on classification and interpretation of features derived from the phonocardiographic (PCG) signal by using advanced signal processing techniques.The PCG signal is traditionally analyzed and characterized by morphological properties in the time domain, by spectral properties in the frequency domain or by nonstationary properties in a joint time-frequency domain. The main contribution of this thesis has been to introduce nonlinear analysis techniques based on dynamical systems theory to extract more information from the PCG signal. Especially, Takens' delay embedding theorem has been used to reconstruct the underlying system's state space based on the measured PCG signal. This processing step provides a geometrical interpretation of the dynamics of the signal, whose structure can be utilized for both system characterization and classification as well as for signal processing tasks such as detection and prediction. In this thesis, the PCG signal's structure in state space has been exploited in several applications. Change detection based on recurrence time statistics was used in combination with nonlinear prediction to remove obscuring heart sounds from lung sound recordings in healthy test subjects. Sample entropy and mutual information were used to assess the severity of aortic stenosis (AS) as well as mitral insufficiency (MI) in dogs. A large number of, partly nonlinear, features was extracted and used for distinguishing innocent murmurs from murmurs caused by AS or MI in patients with probable valve disease. Finally, novel work related to very accurate localization of the first heart sound by means of ECG-gated ensemble averaging was conducted. In general, the presented nonlinear processing techniques have shown considerably improved results in comparison with other PCG based techniques.In modern health care, auscultation has found its main role in primary or in home health care, when deciding if special care and more extensive examinations are required. Making a decision based on auscultation is however difficult, why a simple tool able to screen and assess murmurs would be both time- and cost-saving while relieving many patients from needless anxiety. In the emerging field of telemedicine and home care, an intelligent stethoscope with decision support abilities would be of great value.
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| 23. |
- Ahlström, Christer, 1977-
(författare)
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Processing of the Phonocardiographic Signal : methods for the intelligent stethoscope
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Phonocardiographic signals contain bioacoustic information reflecting the operation of the heart. Normally there are two heart sounds, and additional sounds indicate disease. If a third heart sound is present it could be a sign of heart failure whereas a murmur indicates defective valves or an orifice in the septal wall. The primary aim of this thesis is to use signal processing tools to improve the diagnostic value of this information. More specifically, three different methods have been developed:• A nonlinear change detection method has been applied to automatically detect heart sounds. The first and the second heart sounds can be found using recurrence times of the first kind while the third heart sound can be found using recurrence times of the second kind. Most third heart sound occurrences were detected (98 %), but the amount of false extra detections was rather high (7 % of the heart cycles).• Heart sounds obscure the interpretation of lung sounds. A new method based on nonlinear prediction has been developed to remove this undesired disturbance. High similarity was obtained when comparing actual lung sounds with lung sounds after removal of heart sounds.• Analysis methods such as Shannon energy, wavelets and recurrence quantification analysis were used to extract information from the phonocardiographic signal. The most prominent features, determined by a feature selection method, were used to create a new feature set for heart murmur classification. The classification result was 86 % when separating patients with aortic stenosis, mitral insufficiency and physiological murmurs.The derived methods give reasonable results, and they all provide a step forward in the quest for an intelligent stethoscope, a universal phonocardiography tool able to enhance auscultation by improving sound quality, emphasizing abnormal events in the heart cycle and distinguishing different heart murmurs.
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| 24. |
- Ahlström, Christer, 1977-, et al.
(författare)
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Thresholding distance plots using true recurrence points
- 2006
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Ingår i: Acoustics, Speech and Signal Processing, 2006. ICASSP 2006. - : IEEE. - 142440469X ; , s. 688-691
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Konferensbidrag (refereegranskat)abstract
- Recurrence plots (RP) visualize multi-dimensional state spaces and represent the recurrence of states of a system. Recurrence points can be divided into true recurrence points and false recurrence points (also called sojourn points). We introduce the true recurrence point recurrence plot, TRP, a variant of the traditional RP excluding the sojourn points. This is a cleaned up RP free from recurrence points originating from tangential motion, and hence a more robust representation of unstable periodic orbits. The method is demonstrated with three simple systems, a periodic sine wave, a quasi-periodic torus and the x-component of the chaotic Lorenz system
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| 25. |
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| 26. |
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| 27. |
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| 28. |
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| 29. |
- Alm, Bernt, 1951, et al.
(författare)
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Plötslig oväntad död hos spädbarn. Kunskapsstöd med nationella rekommendationer till hälso- och sjukvården
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- I detta kunskapsstöd presenteras rekommendationer till hälso- och sjukvår-den för rutiner vid plötslig oväntad död hos spädbarn. Vid plötslig oväntad död hos spädbarn bör hälso- och sjukvården använda Socialstyrelsens checklista för anamnesuppgifter använda Socialstyrelsens checklista för statusuppgifter använda Socialstyrelsens checklista för provtagningar och röntgenundersökning. Utredning av plötslig oväntad död hos spädbarn innefattar samverkan mellan tre aktörer med olika uppgifter, nämligen hälso- och sjukvården, Polismyndigheten och Rättsmedicinalverket. Rekommendationerna är avsedda som ett stöd till hälso- och sjukvårdspersonal vid omhändertagandet av det döda barnet och familjen. Rekommendationerna utgör även en grund för utveckling av lokala vårdprogram och de förväntas dessutom bidra till jämlikhet över landet när det gäller utredning samt till att förebygga plötslig oväntad död hos spädbarn. Eftersom det delvis saknas vetenskapliga studier med tillräcklig relevans och kvalitet om utredning av plötslig oväntad död hos spädbarn har Social-styrelsen genomfört en konsensusprocess för att formulera rekommendationerna. Att som förälder påträffa sitt spädbarn livlöst, eller att informeras om att barnet dött, innebär en extrem känslomässig påfrestning. I ett kapitel ger Socialstyrelsen stöd till hälso- och sjukvården med syfte att underlätta informationen till familjen om dödsorsaksutredningen och dödsorsaksdia-gnosen. I ett sista kapitel om stöd till föräldrar under utredningsprocessen ges vägledning om vad som är viktigt att tänka på i mötet med föräldrarna och andra närstående samt vad som bör göras för att utredningen ska bli så komplett som möjligt. I bilagan till kunskapsstödet finns också en beskrivning av de rättsliga förutsättningarna för utredning av plötslig oväntad död hos spädbarn.
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| 30. |
- Andersson, Roger, 1967-, et al.
(författare)
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An asymmetric dialysis tube as an integrated part of a pressure-monitoring sensor
- 2001
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Ingår i: Technology and Health Care. - 0928-7329 .- 1878-7401. ; 9:5, s. 417-425
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Tidskriftsartikel (refereegranskat)abstract
- A sensor has been designed consisting of a tube holder with a force transducer and a tube with a modified cross-section. The holder has a lid that encloses the tube. By having a stiff holder and a compliant tube, the idea is that the intraluminal pressure in the tube can be obtained from the measured force. The method is intended for non-invasive pressure measurements in blood or dialysate tubes.We have used a tube cross-sectional geometry where the outer surface is elliptic and the inner surface is circular with a relation of 2:1 between the thinnest and thickest tube sides. The pressure transducer system shows a linear relationship between the applied pressure and the sensor output (r = 0.999). Within the temperature range, 32°–36°C, which corresponds to the blood and dialysate temperatures, the sensor accuracy is within ±0.8 kPa (±6 mm Hg). This indicates that the sensor should be clinically useful during dialysis and similar applications.
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| 31. |
- Andersson, Roger, et al.
(författare)
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Analysis of the relationship between UV-absorbance of solute contents during a dialysis session
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this paper, the influence from patient anamnesis and haemodialysis session specifications onto the relationship between obtained ultra violet (UV) absorbance and urea concentration in the spent dialysate were discussed. A characterisation of the relationship was done by an intercept value and a slope. Recently, a new a dialysate monitoring device, using UV- absorbance, been developed by our group which has found a relationship between the UV- absorbance and waste products in the dialysate but this relationship vary between patients. In the present investigation, 13 patients performing totally 84 sessions were characterised using 31 possible affecting parameters. Using a multi-regression analysis 11 parameters were found significant as affecting parameters. In a novel mathematical model approach the obtained UV- absorbance and incorporating possible affecting parameters we could predict urea concentration from the UV-absorption in the spent dialysate in the total material of patients and dialysis sessions. For all the 84 sessions R2 between 0.938 and 0.996 were obtained. A performed analysis of variance rejects the assumption of equal conditions for the relationship between diabetics and non-diabetics patients in the material (F=5.2 for intercept and F=14.4 for slope). The urea concentration could be estimated with an accuracy of 11% (one standard deviation) which is normally clinically sufficient. The non-invasive UV -absorption method therefore seems to have great potential for monitoring and control haemodialysis sessions.
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| 32. |
- Andersson, Roger, 1967-, et al.
(författare)
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Cross-sectional changes in an asymmetric tube with bearing on non-invasive pressure measurements
- 2003
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Ingår i: Technology and Health Care. - 0928-7329 .- 1878-7401. ; 11:1, s. 11-20
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Tidskriftsartikel (refereegranskat)abstract
- This study aims at investigating the radial dimensional changes, as a result of an applied intraluminal pressure for an elastic tube with non-uniform cross section. The study is related to a method for non-invasive pressure measurement using the extracorporeal tube as part of the sensor. The intended application is for monitoring of pressure in the blood and dialysate tubes during haemodialysis. The intention is to find a tube cross-section geometry that results in an expansion of the tube so that it is suitable to use as a component in a pressure sensor. The tube should have high radial compliance and expand in a well-defined manner to be able to transfer the intraluminal pressure to a transducer element sensing the radial force. Radial expansion was studied experimentally for tubes with different cross-section geometries. For small tube expansions the resolution in the experimental measurements was not sufficient to study the radial expansion. In this case, numerical simulation was performed. We conclude that a tube with essentially elliptic outer surface and circular inner surface, with a relation of 1:2 between the size of the thin and thick wall, results in a radial expansion upon application of pressure indicating that this tube is suitable for use as part of a sensor.
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| 33. |
- Andersson, Roger, 1967-, et al.
(författare)
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Force to restore the shape of an asymmetric extracorporeal tube as the basis for non-invasive pressure measurements
- 2002
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Ingår i: International Journal of Artificial Organs. - 0391-3988 .- 1724-6040. ; 25:4, s. 281-289
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Tidskriftsartikel (refereegranskat)abstract
- A zero-balance principle is described where intraluminal pressure is estimated from the counter force needed to restore the tube shape of an elastic extra corporeal tube. The aim was to optimise cross-sectional tube geometry for tube expansion due to pressure and to reduce the sensitivity to variation in mechanical tube characteristics using an experimental statistical and factorial design. The main application is pressure monitoring in blood and dialysate tubes during hemodialysis. Improving the monitoring of the dialysis process will reduce complications, such as sudden decreases in systemic blood pressure or occlusion at the artero-venous fistula. The factorial design indicated strong influence from the geometrical characteristics of the tube as well from the geometrical design parameters of the pressure transducer. We found a consistent relationship between the intraluminal pressure and the applied force needed to restore the tube shape. The modified cross-sectional tube geometry enhances measurement sensitivity and facilitates the desired behavior of tubes during pressure applications.
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| 34. |
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| 35. |
- Andersson, R, et al.
(författare)
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Pressure sensed non-invasively directly on the extra corporeal bloodline tube
- 2001
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Ingår i: PROCEEDINGS OF THE 23RD ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY, VOLS 1-4. - 0780372115 ; , s. 3179-3181
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Konferensbidrag (refereegranskat)abstract
- To clinically measure blood pressure at extra corporeal bloodlines involves a hazard due to the infection risk and a risk for thrombosis formation. The aim was to design a non-invasive pressure sensor, measuring directly on a tube section. A modified tube cross-section was used to improve sensitivity. Using the developed sensing principle, a consistent relation (r=0.999) was obtained between pressure and output signal. The output was stable and an acceptable drift within the temperature-range. The method shows great promise for applications in monitoring of the dialysis process.
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| 36. |
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| 37. |
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| 38. |
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| 39. |
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| 40. |
- Ask, Per, et al.
(författare)
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A SHORT-TIME-DELAY URINARY FLOWMETER
- 1985
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Ingår i: Neurourology and Urodynamics. - : Wiley. - 0733-2467 .- 1520-6777. ; 4:3, s. 247-256
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Tidskriftsartikel (refereegranskat)abstract
- A urinary flowmeter has been designed, using a quickly rotating disc and a balance principle. The flowmeter has a fast and accurate response to changing flows. The time delay of the flowmeter is less than about 0.25 s. The improved accuracy in recording urinary flow using the presented flowmeter should make it possible to extract more information from the detrusor pressure and urinary flow relations, relevant for assessing lower urinary tract function.
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| 41. |
- Ask, Per, et al.
(författare)
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A simple device measuring differences in level in the oesophagus
- 1978
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Ingår i: Acta Oto-Laryngologica. - : Informa UK Limited. - 0001-6489 .- 1651-2251. ; 85:3-4, s. 296-297
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- A device for measuring the difference in level between the pressure transducer and a point of measurment is described. It can be used in oesophageal manometry with waterfilled catheters to measure and compensate for superimposed hydrostatic pressure. The practical application of the method is illustrated.
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| 42. |
- Ask, Per, et al.
(författare)
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Accuracy and choice of procedures in 24-hour oesophageal pH monitoring with monocrystalline antimony electrodes.
- 1986
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Ingår i: Medical and Biological Engineering and Computing. - 0140-0118 .- 1741-0444. ; 24:6, s. 602-608
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Tidskriftsartikel (refereegranskat)abstract
- In 24 h pH monitoring, the evaluation is dependent on the absolute accuracy of the pH measurements. Several sources of error exist, such as the chemical composition of calibration buffers and reference electrode gel and the effect of temperature on both the pH and the reference electrodes. We investigated the magnitude of these errors for the monocrystalline antimony electrode. Similar analysis applies to other types of pH electrodes. The errors we found are important when choosing a calibration procedure. We recommend a calibration procedure in which the pH and reference electrodes are both put in a beaker with the calibration buffers prior to and after the 24 h measurements. The calibration buffers and the electrode gel should have a specially selected ion composition where, for example, the Cl-ion concentration is critical. Corrections for differences in temperature between the calibration and the in situ measurements must be added. The pH measurements can be checked by performing in situ calibration.
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| 43. |
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| 44. |
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| 45. |
- Ask, Per, et al.
(författare)
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Bio-acoustic signals from stenotic tube flow : state of the art and perspectives for future methodological development.
- 1995
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Ingår i: Medical and Biological Engineering and Computing. - 0140-0118 .- 1741-0444. ; 33:5, s. 669-675
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Tidskriftsartikel (refereegranskat)abstract
- To study the degree of stenosis from the acoustic signal generated by the turbulent flow in a stenotic vessel, so-called phonoangiography was first suggested over 20 years ago. A reason for the limited use of the technique today may be that, in the early work, the theory of how to relate the spectrum of the acoustic signal to the degree of the stenosis was not clear. However, during the last decade, the theoretical basis for this and other biological tube flow applications has been clarified. Now there is also easy access to computers for frequency analysis. A further explanation for the limited diagnostic use of bio-acoustic techniques for tube flow is the strong competition from ultrasound Doppler techniques. In the future, however, applications may be expected in biological tube flow where the non-invasive, simple and inexpensive bio-acoustic techniques will have a definite role as a diagnostic method.
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| 46. |
- Ask, Per, 1950-, et al.
(författare)
-
Bioacoustic signals from stenotic tube flow
- 1995
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Ingår i: Medical & Biological Engineering & Computing. - : Springer. - 0140-0118 .- 1741-0444. ; 33, s. 669-675
-
Tidskriftsartikel (refereegranskat)
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| 47. |
- Ask, Per, et al.
(författare)
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Bioacoustic techniques is applicable to primary health care
- 2001
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Ingår i: PROCEEDINGS OF THE 23RD ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY, VOLS 1-4. - 0780372115 ; , s. 1911-1914
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Konferensbidrag (refereegranskat)abstract
- The stethoscope has been used diagnostically for nearly two hundred years to assess the heart function. We can envision the intelligent stethoscope which combines the advantages of the traditional instrument with advanced functionality for analysis of the signal and other information support. The bioacoustic technique is basically simple and robust and fits therefore into a scenario where investigations are performed in a distributed health care system as in primary health care or even home health care. We have focused on detection of respiratory sounds and third heart sounds. The later is performed with a new wavelet technique which makes it possible to automatically detect and identify the sounds and possibly relate them to myocardial insufficiency.
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| 48. |
- Ask, Per, 1950-, et al.
(författare)
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Blood flow measurements
- 1999
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Ingår i: The measurement instrumentation sensors handbook. - : CRC Press. - 0849383471
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 49. |
- Ask, Per, et al.
(författare)
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Certification of Clinical Engineers in Sweden
- 2009
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Ingår i: WORLD CONGRESS ON MEDICAL PHYSICS AND BIOMEDICAL ENGINEERING, VOL 25, PT 12. - Berlin, Heidelberg : Springer Science Business Media. - 1680-0737. ; 25:12, s. 430-431
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Tidskriftsartikel (refereegranskat)abstract
- The Swedish Society for Biomedical Engineering and Physics have certified clinical engineers since 1994. The certification is done on tow levels: Master of science and Bachelor of science. We have in total had 614 applications and certified 341 engineers We have certified a total of 341 persons of which 75 are at the master level and 266 at the bachelor level. We are pleased to note that through the years so many engineers have applied and have get a certification. The interest for applying was very large in the beginning but decreased after some years.
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| 50. |
- Ask, Per, 1950-, et al.
(författare)
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Clinical evaluation of different fluid-filled systems for oesophageal manometry
- 1979
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Ingår i: Scandinavian Journal of Gastroenterology. - 0036-5521 .- 1502-7708. ; 14:1, s. 1-5
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Tidskriftsartikel (refereegranskat)abstract
- In a clinical study of oesophageal manometry with fluid-filled catheters, both a non-perfused system and a perfused system with a syringe pump have been compared to a system with a low-compliance perfusion pump, which served as a reference. Significantly lower values of motility amplitudes, motility derivatives, and partly of LES pressures, and a time delay of up to 0.5 sec of the amplitude maximum were obtained with the non-perfused system and the system with a syringe pump in comparison to the low-compliance system. Since the oesophageal function can be erroneously evaluated by use of a non-perfused system or a perfused system with a syringe pump, such systems cannot be recommended for clinical use.
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