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  • Ask, Per, 1950- (författare)
  • Oesophageal manometry : design and evaluation of measurement systems
  • 1978
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The aim of this study was to investigate the technical characteristics of oesophageal manometry systems and to improve the performance of these systems.The investigation of the characteristics of oesophageal manometry systems with non-perfused catheters or catheters perfused with a flow generated by a syringe pump did not show properties which fullfilled the requirements for accurate pressure measurements. The bandwidth of the pressure mesurement system was limited by the high compliance of the syringe perfusion pump. The characteristics of perfused systems were improved by the design of a low-compliance perfusion pump. The frequency characteristics of a pressure measurement system utilizing the low-compliance perfusion pump seemed to be determined by the properties of the cathetermanometer system. The frequency content of oesophageal peristaltic pressure was studied by use of a measurement system including the low-compliance perfusion pump. This investigation showed that a bandwidth of about 8 Hz or more is necessary for accurate measurements, which bandwidth can only be obtained with a low-compliance system. In a clinical study a non-perfused system and a system perfused with a syringe pump were compared simultaneously to a system with the low-compliance perfusion pump. The non-perfused system and the system perfused with the syringe pump gave lower peristaltic and sphincter pressure amplitudes than the system with the low-compliance perfusion pump. Since the oesophageal sphincter pressure varies in different radial directions, a pressure transducer has been devised, the mechanical design of which gives an integration of a radial pressure profile. The transducer has a linear static and dynamic transfer function.
  • Hellgren, Johan, 1966- (författare)
  • Compensation for hearing loss and cancellation of acoustic feedback indigital hearing aids
  • 2000
  • Doktorsavhandling (övrigt vetenskapligt)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.
  • Hällgren, Mathias, 1972- (författare)
  • Hearing and cognition in speech comprehension. Methods and applications
  • 2005
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Central auditory processing is complex and can not be evaluated by a single method. This thesis focuses on assessment of some aspects of central auditory functions by the use of dichotic speech tests and cognitive tests that tax functions important for speech processing.Paper A deals with the cognitive effects in dichotic speech testing in elderly hearing-impaired subjects. It was found that different listening tasks in the dichotic tests put different demands on cognitive ability, shown by a varying degree of correlation between cognitive functions and dichotic test parameters. Age-related cognitive decline was strongly connected with problems to perceive stimuli presented to the left ear.Paper B presents a new cognitive test battery sensitive for functions important for speech processing and understanding, performed in text, auditory and audiovisual modalities. The test battery was evaluated in four groups, differing in age and hearing status, and has proven to be useful in assessing the relative contribution of different input-modalities and the effect of age, hearingimpairment and visual contribution on functions important for speech processing.In Paper C the test battery developed in Paper B was used to study listening situations with different kinds of background noise. Interfering noise at +10 dB signal-to-noise ratio has significant negative effects on performance in speech processing tasks and on the effort perceived. Hearing-impaired subjects showed poorer results in noise with temporal variations, and elderly subjects were more distracted by noise with temporal variations, especially by noise with meaningful content. In noise, all subjects, particularly those with impaired hearing, were more dependent upon visual cues than in the quiet condition.Hearing aid benefit in speech processing with and without background noise was studied in Paper D. The test battery developed in Paper B was used together with a standard measure of speech recognition. With hearing aids, speech recognition was improved in the background condition without noise and in the background condition of ordinary speech. Significantly less effort was perceived in the cognitive tests when hearing aids were used, although only minor benefits of hearing aid amplification were seen. This underlines the importance of considering perceived effort as a dimension when evaluating hearing aid benefit, in further research as well as in clinical practice.The results from the studies contribute to the knowledge about speech processing but also to the search for more specific evaluation of speech understanding, incorporating both sensory and cognitive factors.
  • Johansson, Magnus, 1973- (författare)
  • On noise and hearing loss : Prevalence and reference data
  • 2003
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Noise exposure is one of the most prevalent causes of irreversible occupational disease in Sweden and in many other countries. In hearing conservation programs, aimed at preventing noise-induced hearing loss, audiometry is an important instrument to highlight the risks and to assess the effectiveness of the program. A hazardous working environment and persons affected by it can be identified by monitoring the hearing thresholds of individual employees or groups of employees over time. However, in order to evaluate the prevalence of occupational noise-induced hearing loss, relevant reference data of unexposed subjects is needed.The first part of this dissertation concerns the changes in hearing thresholds over three decades in two occupational environments with high noise levels in the province of Östergötland, Sweden: the mechanical and the wood processing industries. The results show a positive trend, with improving median hearing thresholds from the 1970s into the 1990s. However, the hearing loss present also in the best period, during the 1990s, was probably greater than if the occupational noise exposure had not occurred. This study made clear the need for a valid reference data base, representing the statistical distribution of hearing threshold levels in a population not exposed to occupational noise but otherwise comparable to the group under study.In the second part of the dissertation, reference data for hearing threshold levels in women and men aged from 20 to 79 years are presented, based on measurements of 603 randomly selected individuals in Östergötland. A mathematical model is introduced, based on the hyperbolic tangent function, describing the hearing threshold levels as functions of age. The results show an age-related gender difference, with poorer hearing for men in age groups above 50 years.The prevalence of different degree of hearing loss and tinnitus is described for the same population in the third part of the dissertation. The overall prevalence of mild, moderate, severe or profound hearing loss was 20.9% collectively for women and 25.0% collectively for men. Tinnitus was reported by 8.9% of the women and 17.6% of the men. Approximately 2.4% of the subjects under study had been provided with hearing aids. However, about 7.7% were estimated to potentially benefit from hearing aids as estimated from their degree of hearing loss.Noise-induced hearing loss primarily causes damage to the outer hair cells of the inner ear. The fourth and last part of the dissertation evaluates the outer hair cell function, using otoacoustic emission measurements (OAE). Prevalence results from three different measuring techniques are presented: spontaneous otoacoustic emissions (SOAE), transient evoked otoacoustic emissions (TEOAE) and distortion product otoacoustic emissions (DPOAE). Gender and age effects on the recorded emission levels were also investigated. Women showed higher emission levels compared to men and for both women and men the emission levels decreased with increasing age. The results from the OAE recordings were shown to be somewhat affected by the state of the middle ear. The study included tympanometry, and the relation of the outcome ofthis test to the otoacoustic emissions is described, where high middle ear compliance resulted in low emission level. Reference data for the tympanometric measurements are also presented.The results of this project form an essential part of the important work against noiseinduced hearing loss, which needs continuous monitoring. The reference data presented here will provide a valid and reliable data base for the future assessment of hearing tests performed by occupational health centres in Sweden. This data base will in turn prove useful for comparison studies for Sweden as a responsible fellow EU member country setting high standards for work force safety. The statistical distribution of hearing threshold levels as a function of age for men and women in tabulated form is available on the Swedish Work Environment Authority (Arbetsmiljöverket) web site: http://www.av.se/publikationer/bocker/fysiskt/h293.shtm.
  • Larsby, Birgitta, 1950- (författare)
  • Different neurophysiological methods for studying the vestibular system : evaluation of old methods and development of a new test procedure
  • 1980
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Different methods were used to study the physiology and anatomy of the vestibular system. 1) A primary vestibular cortical area in the cat was located and tested for somatosensory inflow by recordings of vestibular evoked potentials and extracellular single unit activity. 2) The enzyme horseradish peroxidase was used as a retrograde anatomical tracer to identify thalamo-cortical vestibular pathways. 3) Vestibular disturbances aused  by the industrial solvents methylchloroform and styrene were recorded by electro-oculography. Positional nystagmus was seen above a concentration of 75 ppm of methylchloroform and 40 ppm of styrene in blood. 4) A clinical vestibular rotatory test procedure is described and evaluated in an animal model before and after unilateral labyrinthectomy. A long time reduction in gain is seen at higher rotational frequencies and a trend that serves to define the side of a peripheral lesion is superimposed on the oscillatory eye movements after unilateral vestibular damage.
  • Lövsund, Per, 1948- (författare)
  • Biological effects of alternating magnetic fields with special reference to the visual system
  • 1980
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The aims of the present investigation were to contribute to more knowledge of the interaction between extremely low frequency magnetic fields and excitable tissue and to widen the basic understanding of the mechanisms behind these effects. The human visual system and the frog retina were used as model systems.In order to ensure that industrial magnetic flux densities and frequencies were employed in the laboratory studies, the magnetic field levels in the welding and electrosteelindustries at the site ordinarily occupied by the operator were first measured. These processes usually generated fields with a frequency of 50 Hz and a magnetic flux density of 01-10 mT. In the laboratory magnetic fields (0-40 mT, 10-50Hz) were used to induce visual light phenomena, so-called magnetophosphenes, in volunteers. The threshold values for these phosphcnes were detennined as functions of magnetic field frequency as well as of colour and intensity of the background illumination. Maximum field sensitivity occurred at a frequency of approximately 20-30 Hz. With broad spectrum light the threshold flux density was about 10-12 mT. The thresholds were found to be dependent upon the intensity and the spectral distribution of the background light. During dark-adaptation the magnetic field sensitivity decreased. In certain respects volunteers with normal colour vision differed from colour defective ones as far as threshold values are concerned. Possible mechanisms for generation of magnetophosphenes are discussed. The threshold values for magnetophosphenes (0-40 mT) and electrophosphenes (0-0.3 mA) were compared under otherwise identical experimental conditions. In both broad spectrum and monochromatic background lighting the two types of phosphenes had a concurring sensitivity maximum at 20Hz. At higher frequencies there were significant differences in the threshold values. Applying electric current stimulation in different directions did not give rise to any great differences with regard to threshold values within the frequency range 10-30Hz. Frog retinas were exposed to magnetic fields (0-80 mT, 20-30 Hz). The electrical activity in the retina induced by the fields was registered from the ganglion cell layer with the aid of microelectrode technique, whereby a threshold value was obtained at approximately 20 mT and a sensitivity maximum was found at 20 Hz. The magnetic field response occurred within approximately 5 ms, while the light stimulus response occurred only after an average of approximately 85 ms. The latency from light stimulus to response in the ganglion cell layer was significantly prolonged if the preparation was simultaneously and continuously exposed to a magnetic field. Magnetic stimuli similar to light stimuli only induced a response upon 'on', 'off or 'on/off and not during continuous stimulation. Cells which were on-cells during light stimulation became off-cells during magnetic stimulation and vice versa. Addition of Na-aspartate or CoCl2 extinguished simultaneously the response both to light and to magnetic field stimuli. The results indicate that magnetophosphenes are generated in the retina and in the same channels that normally propagate signals induced by light.
  • Nilsson, Gert, 1947- (författare)
  • On the measurement of evaporative water loss : methods and clinical applications
  • 1977
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The new method for measurement of water loss by evaporation from the skin described in paper I, offers a high degree of accuracy and improved sensitivity in comparison with devices reported previously. Rapid recordings can be made by technically untrained persons both in clinical departments and in the laboratory.Using this method, the average insensible perspiration from the skin of healthy adult subjects at rest was found to be 381, 526 and 695 gr per day at ambient temperatures of 22°, 27° and 30°C, respectively. On the head, hands and feet the evaporation rate was high, while on other body surface areas more moderate values were recorded,In a clinical study on newborn infants, a linear relationship between the evaporative water loss from the skin and the ambient humidity was found. At an ambient temperature of 34.5°c and an ambient relative humidity of 50% the average transepidermal water loss was calculated to be 8.1 g/m2h.In burned patients high evaporation rates from about 140 g/m2h to over 220 g/m2h were recorded on the injured skin surfaces. Biological dressings were only slightly permeable to water vapour, while the permeability of the artificial dressings tested was generally high.By recording the rate of increase in vapour concentration in a closed measurement chamber placed over the exposed abdominal cavity during surgery, the water loss by evaporation from wounds and exteriorized viscera was determined. At incisions of minor extent the evaporative water loss was low, while at larger incisions with exteriorized viscera the water loss by evaporation from the wound exceeded the basal cutaneous perspiration of healthy adult subjects.
  • Nilsson, Lena, 1950- (författare)
  • Studies on skin blood flow and evaporative water loss : a bioengineering approach
  • 1986
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Skin blood flow (SBF), temperature, evaporative water loss (EWL) and skin conductance (SC) measured during stimulus-response experiments reveal valuable information regarding the skin's regulatory capacity. SBF and EWL play powerful roles in keeping the human body within an adequate temperature range. EWL and SC reflect the thermal and mental state of the subject. SBF, EWL and SC were measured using noninvasive laser Doppler flowmetry, vapour pressure gradient estimation and a DC-voltage method, respectively.Short acoustic stimuli evoked responses in both EWL and SC at the palm; their response amplitudes were strongly correlated (r = 0.87). Both latency and time to the peak of EWL responses were delayed by 1.1 sec and 2.3 sec, respectively, in comparison to SC responses.EWL measurements at the forearm revealed rhythmical variations in the recorded signal. The period was approximately 0.74 sec at rest. At a higher evaporation rate, induced by exercise, a longer period (0.84 sec) was detected. The period was independent of the sex of the subject and ambient temperature, and remained unchanged for repeated measurements on the same subject.In the skin temperature range 12 to 38°C, the relationship between SBF and local temperature, at the thigh, palm and fingertip, was best fitted to exponential equations. For a narrower temperature interval (23 to 36°C), palmar SBF and temperature followed linear equations within subjects. However, a large variability in regression coefficients was revealed between subjects. When SBF values were normalized to room climate level, they correlated strongly to skin temperature values (r=0.88).Radiative cooling (17°C) of the palm from room climate conditions doubled local heat loss and left SBF virtually unchanged. When cold convective air currents (19°C, 0.5 or 1.0 m/s) were applied, SBF decreased to 60 and 53% while heat loss dropped to 68 and 70%. Rewarming after local cooling revealed discrepancies'in the restoration of both SBF and skin temperature between the measurement sites.
  • Nygårds, Mats-Erik, 1944- (författare)
  • Computer-based detection of cardiac arrhythmias : methods and systems
  • 1983
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The aim of this study was to develop methods and systems which could improve the accuracy or arrhythmia monitoring and analysis of long-term ECGs and eliminate or reduce the need for continuous visual ECG screening. The detection of arrhythmias was based on an automatic classification of heart beats, using waveform features obtained from a basis signals representation. Ventricular fibrillation, a condition in which individual QRS complexes cannot be discerned, was diagnosed from a spectral analysis of the ECG.The methods were put into practice in a computer-based system with the capacity for simultaneous monitoring of eight patients. The accuracy of the system with respect to arrhythmia alarms was studied during ten 24-h periods of clinical routine use, with 55 patients. monitored for a total time of about 1000 h. Seventy percent of the time during which an alarm message should have been present (134 h) a correct alarm was given. An incorrect alarm cause was reported 17% of the time, while 13% of the time no alarm at all was given. The ratio between true and false or incorrect alarms was 3:1.The methods for arrhythmia detection were also utilized in a computer program for offline analysis of long-term ECGs from ambulatory patients. Here, the automatic analysis was combined with a subsequent interactive examination of the analysis results for highest accuracy.
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