| 1. |
- Larsby, Birgitta, 1950-
(author)
-
Different neurophysiological methods for studying the vestibular system : evaluation of old methods and development of a new test procedure
- 1980
-
Doctoral thesis (other academic/artistic)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.
|
|
| 2. |
- Lövsund, Per, 1948-
(author)
-
Biological effects of alternating magnetic fields with special reference to the visual system
- 1980
-
Doctoral thesis (other academic/artistic)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.
|
|
| 3. |
- Nilsson, Lena, 1950-
(author)
-
Studies on skin blood flow and evaporative water loss : a bioengineering approach
- 1986
-
Doctoral thesis (other academic/artistic)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.
|
|
| 4. |
- Nygårds, Mats-Erik, 1944-
(author)
-
Computer-based detection of cardiac arrhythmias : methods and systems
- 1983
-
Doctoral thesis (other academic/artistic)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.
|
|
| 5. |
- Rundquist, Ingemar, 1947-
(author)
-
Cytofluorometry : technique and applications
- 1981
-
Doctoral thesis (other academic/artistic)abstract
- The aims of this investigation were to examine the conditions for rapid fluorescence measurements on cellular material, to improve the performance of measurement systems for microscope fluorometry, and to apply this technique in studies on mast cell biology. Fluorescence fading, a general complication of cytofluorometry, was studied during illumination times in the millisecond range, and a new fading phenomenon characterized by short duration and rapid recovery was described. The findings of the study formed the basis for the construction of two instfurnent systems for microscope fluorometry based on Leitz MPV I and MPV II microscope photometers. Rapid fluorescence measurements were performed by a completely automatic measuring sequence, except forselectionandfocusing of the objects to be measured. Automation was mainly achieved by the integration of computers in the measurement systems, which also resulted in easily interchangeable programdetermined measuring routines and proper data processing and presentation of results. The systems were mainly used for rapid analysis of cell populations. The precision of the measurements was improved by different standardization techniques, and the measuring speed, about 500 cells per h on well prepared specimens, was high enough to permit analysis of relatively large cell populations within a reasonable time.The cytofluorometric technique was applied to studies on the biology of the connective tissue mast cell. Rat peritoneal mast cells were used for this purpose. The proliferation of mast cells was estimated by cytofluorometric measurements of DNA in mast cell populations after staining with the fluorescent dye Hoechst 33258. Formaldehyde-induced fluorescence was used to study the uptake and turnover of dopamine in mast cells in vivo. Measurements of the mast cell content of heparin, a constituent of the mast cell granule matrix, were performed by a combination of microscope fluorometry, which permits visual identification of the cells, and flow cytofluorometry, by which rapid measurements of large populations can be made.
|
|
| 6. |
- Salerud, Göran, 1954-
(author)
-
Laser doppler tissue flowmetry : fiberoptic methods in microvascular research
- 1986
-
Doctoral thesis (other academic/artistic)abstract
- Laser Doppler flowmetry (LDF) constitutes a method for measuring the flux of blood cells in the microcirculatory bed. Photons are scattered in the moving blood cells, where they undergo a frequency shift according to the Doppler principle. Light is brought to the tissue under study by one optical fiber and transmitted back to photodetectors by two separate fibers. LDF is a particulary useful method to study blood flow patterns and vascular regulatory mechanisms, since it is non-invasive and assesses blood flow in a very small volume of tissue (1 mm3).Blood flow recordings from skin areas, such as forearm and forehead, have revealed large spatial and temporal variations in microvascular blood flow. If the flowmeter probe is moved as little as 2.5 mm, the spatial heterogeneity of the vasculature result in a significant (p<0.001) difference in flowmeter output signal.Spontaneous rhythmical blood flow patterns (vasomotion) with different amplitudes, appeared in all of the 8 subjects studied. Some subjects had a continuous vasomotion pattern, while others showed only "bursts" of the pattern. Recorded blood flow in two juxtaposed skin sites sometimes demonstrated simultaneous variations in both sites, while in other instances the rhythmical flow patterns were out of phase or of different frequencies. To overcome the problem with a large spatial variation in skin blood flow in relation to the geometrical dimension of the probe, a multifiber probe was developed. It was designed to integrate the blood flow over an area enlarged approximately seven times compared to the standard probe. Measurements with this probe reduced the spatial differences as theoretically expected. No averaging effect was found, however, on the temporal variations.In skin, the capillary bed is located superficially, while in other tissues, such as the intestine, the inner wall (mucosa) is the most perfused. In an experiment on cat small intestine, the blood flow was measured both from the mucosal and serosal side. The results showed that it was possible to record the total blood flow of the intestinal wall, irrespective of whether the probe was placed on the mucosal or serosal side of the bowel wall.For tissues like muscle, liver and brain it may be of interest to assess the deep tissue perfusion. The LDF standard probes are, however, too large and blunt to be inserted into the tissue, without disturbing the flow. Therefore a single fiber LDF was developed, with oneoptical diber (Ø =0.5 mm) guiding the light to and from the tissue under study. In a flow model resembling tissue perfusion, the usefulness of the single fiber LDF based on the differential technique was evaluated. When a mathematical model was used to evaluate the single versus the differential channel operation, the differential technique was found most powerful if the laser broadband noise has a substantial rms-value or if many coherence areas are detected. The dynamic responses of the single fiber LDF were studied in a pig experimental model under different physiological conditions. The results agreed well with known reference blood flow patterns
|
|
| 7. |
- Stål, Olle, 1952-
(author)
-
Static and flow cytometry for tumor DNA analysis
- 1989
-
Doctoral thesis (other academic/artistic)abstract
- The analysis of cellular DNA content in human tumors has shown to be of prognostic importance. The techniques used involve measurements in slide preparations by absorption cytophotometry and static cytofluorometry as well as the analysis of cell suspensions by flow cytometry. The aim of this work has been to improve these techniques by the development of computer aided systems in order to facilitate the use in a larger scale for clinical purposes. Another aim has been to study the prognostic significance of DNA analysis in breast cancer.Software for determination of DNA content and nuclear area by scanning absorption cytophotometry was developed. The system, HISTOSCAN, is insensitive to light scattering and may therefore be used in tissue sections. Thus, measurements in morphologically well-defined areas may be performed, but the method is less suitable for extensive use due to the slow procedure of the mechanical scanning.More rapid analyses are achieved by the system developed for static cytofluorometry in cytocentrifuged specimens. Cells to be measured are not positioned in the ordinary way, but are just passed through the excitation light beam as the specimen is visually scanned. DNA content and nuclear size are estimated simultaneously from the fluorescence recorded. For estimation of proliferative activity a sufficient number of cells may be analysed within a reasonable time.Similar results were obtained by static cytofluorometry and flow cytometry in a series of primary breast cancers. A close correlation was found for DNA index and, if 200 cells or more were measured, the same was true for S-phase fraction.Tumors from 472 women with primary breast cancer were analysed by flow cytometry. DNA ploidy showed significant association with disease recurrence and mortality but did not show a prognostic value in addition to that of traditional factors. The prognostic significance of S-phase fraction was independent of nodal status, tumor size and estrogen receptor content concerning early relapse and mortality. The survival of 116 women with recurrent breast cancer was correlated with both DNA ploidy and S-phase fraction in a multivariate analysis including nodal status, tumor size, ER content and site of recurrence.
|
|
| 8. |
- Sundqvist, Tommy, 1949-
(author)
-
Probing intestinal permeability in man using different-sized, low-molecular-weight polyethyleneglycols and mathematical modelling
- 1981
-
Doctoral thesis (other academic/artistic)abstract
- Selective intestinal permeability as reflected by the urinary recovery of low-molecular-weight polyethylene glycols (PEG 400) of dlfferentsizes after oral administration was characterized with a mathematical filter-function. There was relative loss of both large and small PEG molecules on their way from the intestine to the urine. The reduced recovery of the large molecules is explained by selective intestinal absorption, since intravenous instillation abolished the effect. After curve-fitting to the experimental data, the mathematical procedure gives a quantitative measure of the fraction of selective and non-selective passage, and of filter-efficiency at different molecular weights. When applied to patients treated by bypass surgery for morbid obesity the method indicated a less permeable intestine with a reduced effective absorbtive surface area. In patients with rheumatoid arthritis a fasting diet gave a similar effect, which was accompanied by a reduction in disease activity. However, after changing to lactovegetarian diet the intestinal selectivity returned towards the control values, as did the inflammatory indices. Finally, to evaluate the importance of different physiological criteria for the outcome of the PEG 400 absorption test, a mathematical multi-compartment model was constructed and simulated on a computer.
|
|
| 9. |
- Tenland, Torsten, 1952-
(author)
-
On laser Doppler flowmetry : methods and microvascular applications
- 1982
-
Doctoral thesis (other academic/artistic)abstract
- A laser Doppler flowmeter for non-invasive microcirculatory blood flow studies has been developed. The tissue under study is illuminated by laser light (helium-neon laser, output power 2 mW) via an optical fibre and the Doppler shift oflight scattered in moving red cells is analysed. By the use of two photodetectors for detection of the backscattered light, the influences of mode interference and broadband noise from the laser and noise from surrounding light sources have been suppressed. The instrument is designed to give a continuous, stable and linear real-time measure of the flux of red cells (i.e. the number of red cells times their velocity) in the outermost layer (1 mm) of tissue, in which the red cell volume fractions are low or moderate. Linearity, measuring depth and the influence of blood oxygen tension were evaluated in a flow model with optical properties similar to those of human skin. Laser Dopplerflowmetry was found to be versatile for measurements of blood flow in human skin and rat testis and did not influence the flow under study.An extensive study of spatial and temporal variations of human skin blood flow was performed. As it was found that skin blood flow shows wide day-to-day variations and significant differences between adjacent probe sites, earlier reported "normal" values of skin blood flow were seriously questioned. It is proposed that this study can serve as a base for further functional studies.Testicular blood flow in rats was studied in order to evaluate acute effects of stress-linked substances such as adrenaline and noradrenaline. Both substances lowered the blood flow at high doses.Rhythmical variations of blood flow (frequency 5-12 min-1) in human skin and rat testis were observed and found to be in agreement with earlier findings in microscopic studies on other types of tissue. The nature and origin of this rhythmicity point towards a local regulatory mechanism operating also under "steady state" conditions.
|
|
| 10. |
- Åhlfeldt, Hans, 1955-
(author)
-
Computer-based modeling and simulation in the analysis of cardiac arrhythmias and cardiac pacing
- 1989
-
Doctoral thesis (other academic/artistic)abstract
- Most systems for ECG analysis deal with QRS classification and arrhythmia detection but do not address the problem of finding the underlying mechanism responsible for the manifest arrhythmia. Although it is possible to distinguish among different arrhythmogenic mechanisms on the cellular level, it is far more difficult in the clinic based on ECG recordings. A computer model which is well suited for rhythm studies has been developed. The heart is modeled as a network of finite elements in which the impulse propagation is described mathematically, as well as several arrhythmogenic mechanisms. These include modulated parasystole, macro and micro reentry and different kinds of block. Since modulated parasystole provides a unified explanation of a variety of different arrhythmias, a stepwise procedure is presented by which this mechanism can be detected. Modulated parasystole can be described mathematically with a phase response curve, and the model has proven valuable for deduction of biand triphasic phase response curves from clinical cases with frequent ventricular premature complexes.Cardiac pacing is a very important therapy for rhythm disorders and since modern pacemakers interact with the heart in a complex way, the problem of cardiac pacing and pacemaker follow-up has also been studied. An ambulatory recording system has been developed, including a pacemaker spike detector and a computer program which can detect possible events of pacemaker malfunction. The computer model has been used to analyse the interaction between the heart and different types of pacemakers. The model has also been integrated with a hypertext system, allowing the system to be used for computer-aided education of cardiac pacing and cardiac arrhythmias.
|
|
