| 1. |
- 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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| 2. |
- Hellgren, Johan, 1965
(författare)
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Non-infectious rhinitis. Epidemiology and clinic
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We have assessed self-reported rhinitis in the absence of common cold, called "Non-infectious rhinitis", (NIR). The occurrence of NIR was investigated in a population sample of 2,044 individuals, aged 21-51, in an industrialised county in Sweden who answered a questionnaire relating to NIR and occupational exposure to potential irritants and sensitisers. For the clinical evaluation of NIR we compared four different, objective methods to assess nasal obstruction in 41 subjects without current nasal symptoms. Two of these methods, peak nasal inspiratory flow (PNIF) and acoustic rhinometry were used to assess objective signs of rhinitis in 37 workers exposed to paper dust compared with 36 controls in a soft-paper industry. Finally we assessed subjective and objective signs of rhinitis, including the quality of life, in a population sample of 184 individuals with asthma, compared with controls.The prevalence of NIR in a general population was 40% while the incidence rate was 13.5/1,000 person-years. Smokers, subjects with atopy and women had a higher incidence rate of NIR. Men exposed to fire fumes, male cleaners and women exposed to paper dust also ran an increased risk of NIR. The clinical study confirmed that workers exposed to paper dust had more symptoms of nasal blockage and nasal crusts that deteriorated during the working day, but we found no objective signs of nasal inflammation. Among the subjects with asthma we found an increased reversible swelling of the nasal mucosa. Subjects with asthma and NIR also experienced more deterioration in their quality of life than those without NIR.Conclusion; these results indicate that NIR is common in a general population. Occupational exposure to paper dust and asthma was associated with an increased risk of NIR.
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| 3. |
- Hellgren, Karl-Johan
(författare)
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A New Model for Assessment of Change in Visual Function in Diabetes
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The purpose of this thesis was to determine whether perimetry using a new model to interpret deterioration or improvement in the visual field can be employed to assess change in visual function over time in diabetes. Diabetic retinopathy has long been considered a microvascular disease, but it is still a matter of debate to what extent diabetes also affects retinal neurons. Visual acuity is routinely tested to evaluate visual function in diabetes, but can vary for no obvious reasons and even be normal despite severe vessel abnormalities, and hence less useful for early detection of visual impairment. Until now, no measure has proven to be suitable for identifying early changes in retinal function in diabetes. Two cohorts were investigated. The first cohort comprised 55 diabetic patients with various degrees of diabetic retinopathy. Using a cross-sectional design, we studied how refraction and visual acuity varied in patients under routine care (Study I), and we assessed limits for significant change in visual fields by use of standard automated perimetry (SAP) and short-wavelength automated perimetry (SWAP) based on short-term test–retest variability (Study II). The second cohort consisted of 81 diabetic subjects with no or mild/moderate diabetic retinopathy. We applied a longitudinal prospective design to explore the correlation between functional change and progression of microvascular abnormalities (Study III), and examined the usefulness of SAP with our limits of significant change for detecting early retinal dysfunction over 3–5 years (Study IV). In Study I, we demonstrated that refraction was stable in most eyes, and assessments of visual acuity were highly reproducible despite substantial fluctuations in blood glucose levels. In Study II, we defined limits of significant change for SAP and SWAP for diabetic subjects. In Study III, we used the defined limits for change to monitor visual function in diabetes by SAP. After 18 months of follow-up, deterioration was common but improvement was rare, and deteriorated fields were reproducible despite an unchanged degree of retinopathy. In Study IV, up to five years of follow-up, confirmed visual field deterioration in eyes without any retinopathy or with stable mild/moderate retinopathy. Standard automated perimetry with our new model for detecting change can successfully determine early retinal dysfunction over time in diabetes, which can represent early signs and progression of retinal neurodegeneration.
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| 4. |
- Quist, Johan, 1971-
(författare)
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Att översätta TQM : - en longitudinell studie kring reflekterande aktörer
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This doctoral thesis focuses on translating Total Quality Management (TQM). The reason for this focus is that ideas such as TQM rarely or never contain a complete description of how the idea is to be “installed” in an organisation if it is to achieve the intended result. This often has the consequence that the result the idea is expected to produce in the organisation is only achieved in part, if at all. In Sweden there has been a great interest in working with the SIQ Model for Performance Excellence. In the thesis the model is viewed as an operationalisation of the TQM concept.The theoretical perspective of sensemaking is applied to understand what happens when organisations begin to use the model. This work is in the thesis seen as a translation process and contrasts the rational view of implementation. The sensemaking perspective rests on a social constructionist viewpoint, which distinguishes it from the view that TQM has on organisations. The study is placed in the interpretative paradigm and two service organisations in public sector have been studied with a longitudinal design.The main contribution of the study is a new way of looking at the work with the model. Thus, the interpretations could be seen as aspects, which together present a detailed description of the translation process. These aspects are, in summary, a way of looking upon and understanding:• the translation process as a number of parallel and reciprocal processes• the role of the translators• the relationship between translators and top management• the contextual prerequisites of the translation process.In addition to this, the thesis can work as a driving force towards a more constructive and critical attitude among practitioner of TQM. The somewhat seductive rhetoric and the risk to work with the model without an apparent intention are highlighted in the study. It seems that the model in itself can lead to collective sensemaking that gets the work done without discussing the intention. In light of the interpretations it becomes clear that working with the model is a relatively complicated process. Many of the failed attempts to reach excellence could be explained by unrealistic expectations of the character and requirement of the work. In the thesis, the translator has been introduced as a counterbalance that possibly could help dealing with the complexity of TQM.
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| 5. |
- Sjölander, Isabella
(författare)
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Pediatric Obstructive Sleep Apnea : Evaluation of surgical treatments and immunological aspects
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Pediatric obstructive sleep apnea (OSA) is a sleep-related breathing disorder often caused by enlargement of the adenoid and the tonsils. The peak prevalence is among children who are two to six years of age, when the lymphatic tissue is most active. Clinical diagnosis can be challenging, since the symptoms are often unspecific. Polysomnography, the diagnostic gold standard is a complex procedure with limited availability.The standard surgical treatment for OSA is removal of the tonsils (tonsillectomy) together with removal of the adenoid (adenoidectomy). Partial removal of the tonsils together with adenoidectomy, known as adenotonsillotomy, is a treatment accompanied with less postoperative morbidity but a higher risk of reoperation. The aims of this thesis are to evaluate different treatment methods for treating pediatric OSA and to investigate immunological aspects of tonsil hypertrophy.In Paper I, tonsil tissue from children with large tonsils and moderate to severe OSA was compared with tonsil tissue from children with small tonsils and milder OSA. The tissue was analyzed with flow-cytometry using markers for T cells, B cells and ILCs. Patients with enlarged tonsils and more severe OSA had a significant increase of naïve B cells without a difference in the Ki67 proliferation marker. This indicates an impaired differentiation and/or migration of B cells in the larger tonsils.In Paper II, behavior and mental health after adenotonsillectomy or adenotonsillotomy were compared. Together with polysomnography and the questionnaire OSA-18, a strength and difficulties questionnaire (SDQ) was filled out both before and one year after treatment. No significant differences between the treatment groups were seen after one year, in terms of mental health and behavior. Paper III is a long-term follow-up study of a previously published randomized controlled trial of adenotonsillectomy and adenotonsillotomy. Five years after surgery, a new polysomnography was performed on the patients. The results showed a high dropout rate, and six children were excluded because of re-operation with adenotonsillectomy. No difference in the obstructive apnea hypopnea index was found between the groups five years after surgical intervention.Paper IV is a prospective cohort study of children treated for OSA. The correlations between subjective data from OSA-18, patient-reported outcome measures, and objective data from polysomnography were compared. Significant correlations were shown between changes in objective polysomnography data and changes in OSA-18, with the strongest correlation in the sleep disturbance subscale. The measure of patient-reported outcomes showed a significant but weak correlation.
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| 6. |
- Thunberg, Ulrica, 1967-
(författare)
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Aspects of Staphylococcus aureus in Chronic Rhinosinusitis
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Chronic rhinosinusitis (CRS) affects about 10% of the European population, and is considered a great scourge. Its cause is not clear. Findings of Staphylococcus aureus in the maxillary sinus are common in CRS patients, but are usually regarded as insignificant due to the bacterium’s attribute as a commensal elsewhere. S. aureus has the ability to cause both mild disease and serious conditions, due to its wide armoury of secreted components such as staphylococcal enterotoxins and cell-surface-associated virulence components. This thesis focuses on the clinical features and importance of S. aureus in CRS, including a long-term perspective on the disease, through studying a cohort of CRS patients. S. aureus was found to be highly prevalent in the maxillary sinus and nares of CRS patients, which might indicate an impact on the disease. A sheltered sampling technique for maxillary sinus culture reduced the contamination rate but did not significantly improve the diagnostic reliability. Whole genome sequencing showed that 95% of paired S. aureus isolates collected simultaneously from the nares and maxillary sinus were from identical lineages, indicating colonization of the maxillary sinus from the nares as one joint milieu. A decade-long persistence of S. aureus in the nares and maxillary sinus was established in 20% of CRS patients. The vast majority of S. aureus isolates were susceptible to all tested antibiotics, including the strains that had persisted for a decade. No significant differences in the prevalence of gene determinants were seen for selected virulence factors and MSCRAMMs in S. aureus isolates sampled from CRS patients and healthy controls. The overall alterations of anti-staphylococcal antibodies over time showed great variability and minor support for an impact of S. aureus on CRS. At the long-term follow-up, symptoms were generally reduced and VAS quality of life in terms of fatigue was improved. The subgroup of CRS patients without nasal polyposis had a greater chance of symptom relief than their counterparts with nasal polyposis in this longterm perspective. There was no correlation between severity of symptoms for CRS patients and S. aureus growth in the maxillary sinus to support a role for S. aureus in CRS.
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