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| 2. |
- Arlinger, Stig, 1939-, et al.
(författare)
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Clinical trial of a digital hearing aid
- 1998
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Ingår i: Scandinavian Audiology. - : Taylor & Francis. - 0105-0397 .- 1940-2872. ; 27:1, s. 51-61
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Tidskriftsartikel (refereegranskat)abstract
- A clinical trial of Oticon DigiFocus hearing aid was performed. The test aid was evaluated on 33 subjects with several years' experience as users of modern analog hearing aids. These aids were used as reference for the 1-month-long trial. The Abbreviated Profile of Hearing Aid Benefit (APHAB) showed a mean difference in benefit with superior ratings for the test aid concerning ease of communication, speech in reverberation and speech in background noise. The subjects' own aids were rated somewhat better concerning aversiveness of sounds, but this difference was not statistically significant. The Gothenburg Profile showed a statistically significant difference between the test aid and the reference aids in favour of the test aid. The difference was not most evident with regard to speech communication and the effects of hearing loss on social interactions. Sound quality ratings concerning clearness were significantly higher for the test aid. Speech recognition thresholds in noise were on average 0.7 dB better for the test aids when tested at speech levels 60 and 75 dB. The difference was statistically significant only at 75 dB. There was significant interaction between general preference and hearing aid type, indicating that overall sound quality was an important factor affecting the general preference for either the test aid or the reference aid. Twenty-three subjects generally preferred the test aid, six preferred their own aid and four stated no difference.
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| 3. |
- Askling, Helena H, et al.
(författare)
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Serologic Analysis of Returned Travelers with Fever, Sweden
- 2009
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Ingår i: Emerging Infectious Diseases. - Atlanta, GA, USA : U.S. Department of Health and Human Services * Centers for Disease Control and Prevention. - 1080-6040 .- 1080-6059. ; 15:11, s. 1805-1808
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Tidskriftsartikel (refereegranskat)abstract
- We studied 1,432 febrile travelers from Sweden who had returned from malaria-endemic areas during March 2005-March 2008. In 383 patients, paired serum samples were blindly analyzed for influenza and 7 other agents. For 21% of 115 patients with fever of unknown origin, serologic analysis showed that influenza was the major cause.
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| 4. |
- Braun, Oscar Ö., et al.
(författare)
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Continuous-flow LVADs in the Nordic countries : complications and mortality and its predictors
- 2019
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Ingår i: Scandinavian Cardiovascular Journal. - : Informa UK Limited. - 1401-7431 .- 1651-2006. ; 53:1, s. 14-20
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: The purpose of this study was to assess complications and mortality and its predictors, with continuous-flow left ventricular assist devices (CF-LVADs) in the Nordic Countries.Design: This was a retrospective, international, multicenter cohort study.Results: Between 1993 and 2013, 442 surgically implanted long-term mechanical assist devices were used among 8 centers in the Nordic countries. Of those, 238 were CF-LVADs (HVAD or HeartMate II) implanted in patients >18 years with complete data. Postoperative complications and survival were compared and Cox proportion hazard regression analysis was used to identify predictors of mortality. The overall Kaplan-Meier survival rate was 75% at 1 year, 69% at 2 years and 63% at 3 years. A planned strategy of destination therapy had poorer survival compared to a strategy of bridge to transplantation or decision (2-year survival of 41% vs. 76%, p < .001). The most common complications were non-driveline infections (excluding sepsis) (44%), driveline infection (27%), need for continuous renal replacement therapy (25%) and right heart failure (24%). In a multivariate model age and left ventricular diastolic dimension was left as independent risk factors for mortality with a hazard ratio of 1.35 (95% confidence interval (CI) [1.01-1.80], p = .046) per 10 years and 0.88 (95% CI [0.72-0.99], p = .044) per 5 mm, respectively.Conclusion: Outcome with CF LVAD in the Nordic countries was comparable to other cohorts. Higher age and destination therapy require particularly stringent selection.
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| 5. |
- Hellgren, Johan
(författare)
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Analysis of feedback cancellation in hearing aids with Filtered-X LMS and the direct method of closed loop identification
- 2002
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Ingår i: IEEE transactions on speech and audio processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1063-6676 .- 1558-2353. ; 10:2, s. 119-131
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Tidskriftsartikel (refereegranskat)abstract
- Feedback cancellation in hearing aids based on Filtered-X LMS is analyzed. The data used for identification of the feedback path is the output and input signals of the hearing aid. The identification is thus done in closed loop. Tracking characteristics and bias of the optimal estimate are discussed. The optimal estimate can be biased when the identification is performed in closed loop and the input signal to the hearing aid is not white. It is shown that the bias could be avoided if the spectrum of the input signal was known and the data used to update the internal feedback is prefiltered. The effects of different choices of the design variables of the Filtered-X LMS are discussed. Three alternatives of the fixed filter were evaluated on feedback paths of hearing aids on human subjects and with alternative spectra of the input signal. The optimal estimate of the Filtered-X LMS with an individually adjusted fixed filter showed the best agreement with the desired estimate.
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| 6. |
- Hellgren, Johan, 1966-, et al.
(författare)
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Bias of feedback cancellation algorithms in hearing aids based on direct closed loop identification
- 2001
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Ingår i: IEEE transactions on speech and audio processing. - : Institute of Electrical and Electronics Engineers (IEEE). - 1063-6676 .- 1558-2353. ; 9:8, s. 906-913
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Tidskriftsartikel (refereegranskat)abstract
- The undesired effects of acoustic feedback of hearing aids can be reduced with an internal feedback path that is an estimate of the external feedback path. This paper analyzes the limiting estimate of the feedback for feedback cancellation schemes that apply some recursive prediction error method with a quadratic norm, e.g., least mean square (LMS) and recursive least squares (RLS), to the output and input signals of the hearing aid to identify the feedback path. The data used for identification is then collected in closed loop and the estimate used in one recursion will affect the data used in succeeding recursions. These properties have to be considered in the analysis. The analysis shows that the limiting estimate may be biased if there is an error in the used model of the input signal to the hearing aid, and that the system is not identifiable unless a second input signal to the system is added to the output of the hearing aid or the signal processing of the hearing aid used to modify the signal to the impaired ear is nonlinear. The limiting estimate is presented as the solution to an optimization problem in the frequency domain. An analytical expression of the limiting estimate is presented for a special case. For other cases an algorithm is presented that can be used to find a numerical solution. The results can be useful when the model structure used with the recursive identification is chosen.
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| 7. |
- Hellgren, Johan, 1966-
(författare)
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Compensation for hearing loss and cancellation of acoustic feedback indigital hearing aids
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The development of integrated circuits during the last decades has made it possible to incorporate digital signal processing in hearing aids that fit into the ear canal and are powered by small zink-air batteries. The digital signal processing provides new possibilities for the hearing aid to modify the signal to fit the impaired ear. A linear phase filter bank that is intended as a basic building block of the signal processing in digital hearing aids is introduced in this dissertation. The filterbank is computationally very efficient and divides the input signal into a number of narrow band signals for further signal processing. The filter bank was combined with band specific gains and two compressors to form the signal processing of a hearing aid. The compressors allow leveldependent gain. Three alternative fitting strategies used to adjust the characteristics of this hearing aid to the individual hearing impaired listener were evaluated. The three fitting strategies differed mainly in the characteristics of the compressors. The strategies were evaluated by hearing impaired subjects in a field test and in laboratory tests. When the subjects were grouped according to their preference among the fitting strategies, the results showed significant differences in the hearing loss configuration between the groups.One of the main tasks of a hearing aid is to amplify the signal to make it audible for the hearing impaired user. The maximum gain that can be used in a hearing aid will be controlled by the feedback from the output to the microphone, as the hearing aid will be a part of a closed loop system. The feedback path depends on several factors such as the position of the microphone (differs between hearing aid categories), size of vent, and the acoustics around the hearing aid. The feedback, and thus the maximum gain that can be used in a hearing aid, has been identified with a number of different hearing aids in a number of conditions that can be expected when the hearing aid is used under real-life conditions.Feedback cancellation can be used to reduce the negative effects of feedback on the performance of the hearing aid. An internal feedback in the hearing aid that is an estimate of the external feedback is then used to cancel the feedback signal. The external feedback path will vary as the hearing aid is used ( e.g. when a telephone set is placed by the ear). It is thus desirable to continuously identify the feedback path. One approach to do this is to utilize closed loop identification with the direct method and some recursive identification method. The output and input signals of the hearing aid are then considered as input and output signal of the system to be identified, i.e. the feedback path. An advantage with this method is that the identification can be done without modifying the output signal. A drawback is that the estimate may be biased, depending on the characteristics of the input signal. A difference from many other closed loop identification problems is that the data used for identification will depend on previous estimates of the system. A feedback cancellation algorithm where Filtered-X LMS is used with the direct method has been analyzed. Filtered-XLMS is computationally efficient and gives a possibility to incorporate known characteristics of the feedback path in the model set used. Prefiltering was also used in the algorithm as it can provide an unbiased estimate if the spectrum of the input signal is known.
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| 8. |
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| 9. |
- Hellgren, Johan, 1966-, et al.
(författare)
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Variations in the feedback of hearing aids.
- 1999
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Ingår i: Journal of the Acoustical Society of America. - 0001-4966 .- 1520-8524. ; 106, s. 2821-2833
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Tidskriftsartikel (refereegranskat)
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| 10. |
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