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- Nilsson, Lena, 1950-
(author)
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Studies on skin blood flow and evaporative water loss : a bioengineering approach
- 1986
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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.
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| 2. |
- Salerud, Göran, 1954-
(author)
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Laser doppler tissue flowmetry : fiberoptic methods in microvascular research
- 1986
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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
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| 3. |
- Stål, Olle, 1952-
(author)
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Static and flow cytometry for tumor DNA analysis
- 1989
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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.
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| 4. |
- Åhlfeldt, Hans, 1955-
(author)
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Computer-based modeling and simulation in the analysis of cardiac arrhythmias and cardiac pacing
- 1989
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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.
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| 5. |
- Lennmarken, Claes, 1948-
(author)
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Skeletal muscle function and energy metabolism in various nutritional states : a clinical study
- 1986
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Doctoral thesis (other academic/artistic)abstract
- The clinical picture of the malnourished patient consists of loss of body fat and lean body mass resulting in weight loss and impaired vital organ function. Weakness and fatigue are often prominent symptoms arising from affected skeletal muscle in these patients.Skeletal muscle is intimately involved in the process of body energy metabolism and its regulation. The effect of insufficient nutritional intake on skeletal muscle function and energy metabolism was studied in subjects, with various nutritional states. Involuntary muscle function was assessed in the adductor pollicis muscle after electrical stimulation of the ulnar nerve. Energy metabolites were measured in needle biopsy samples from the quadriceps femoris muscle.After total starvation, muscle function was found to be altered and indicated a low rate of energy turn-over. In extremely obese patients, muscle function was also changed but indicated a high rate of energy turn-over. Semi-starved surgical patients had normal skeletal muscle function.In anorexia nervosa patients 3-5 weeks of total patenteral nutrition largely normalized their deranged muscle energy metabolism. In the obese patients energy metabolism was found to be altered, indicated a high metabolic rate. This is probably a physiological adaptation to a high body weight. In semi-starved surgical patients normal contents of energy metabolites were found.These findings indicate that major changes in the nutritional state, induced alterations in skeletal muscle energy metabolism. Skeletal muscle function was concomitantly altered indicating a relationship between energy metabolism and function in skeletal muscle. In moderately malnourished patients however, skeletal muscle function was normal.
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| 7. |
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| 8. |
- Timpka, Toomas, 1957-
(author)
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Design of computer-based decision support for general practitioners
- 1989
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Doctoral thesis (other academic/artistic)abstract
- Most computer-based decision support systems (DSSs) in medicine have been developed in hospital settings, intended for use in hospitals. In this study, a DSS for general practitioners (GPs) in primary care is designed, taking into consideration that primary care is the first level in a health care organization. Female genitourinary (GU) infections is chosen as prototype area for the study of decisionmaking. There are three primary data sources used for this study: 1. Decision protocols were obtained from 11 GPs after 139 GU consultations. A decision certainty estimate and an estimate by the GP of the patient's desire to go through GU work-up was included. 2. A nine-physician panel evaluated 63 of these protocols. Individually, the panel completed a similar decision protncol without access to the GP's decisions. 3. Questionnaires were responded to by 186 primary care physicians regarding information needs and attitudes towards computer support. The critical incident technique is used to identify information dilemmas. Discriminant analysis is used to identify dati items used by the GPs to differentiate between decision alternatives. The kappa coefficient is used as measure of inter-physician decision variability in the panel. From a theoretical review, a model is establisbed,of which knowledge types the GP uses and the forms in which this knowledge is used in daily practice:Not all types of knowledge relevant to the GP are available in forms amenable to computer manipulation. Doctor-patient communication skills are, for instance, tacit and acquired through professional experience. The main empirical results of this study are that: I. The GPs rely heavily on laboratory data in their decisions. However, they fail to use negative evidence. Orthogonal patient desire is a major source of uncertainty. 2. The urethritis diagnosis is used inconsistently. 3. There are considerable differences between individual physicians in their use of medical concepts. In one case out of four, no consensus diagnosis is available at all. 4. Dilemmas in general inte'rnal medicine are the most prevalent medicaldilemmas for the GP, and support for drug prescription and access to full-text databases are the computer applications most desired. A design of the DSS is described, which consists of five integrated components: a hypertext module, a critiquing program for support of drug prescriptions, diagnosis support of reconsider type, an interface to computer-based library and communication resources, and a central database. The design is implemented in experimental form. Organizational changes to facilitate decision-making and a theoretical model of the GP's information use arc discussed.
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