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- Bergstrand, Sara, 1978-
(författare)
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Preventing pressure ulcers by assessment of the microcirculation in tissue exposed to pressure
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overall aim of this thesis was to combine optical methods into a system with the ability to simultaneously measure blood flow changes at different tissue depths. The goal of such a system was to reveal vascular mechanisms relevant to pressure ulcer etiology under clinically relevant conditions and in relation to the evaluation of pressure-redistribution support surfaces.This thesis consists of four quantitative, cross-sectional studies measuring blood flow responses before, during, and after pressure exposure of the sacral tissue. Two optical methods – photoplethysmography and laser Doppler flowmetry – were combined in a newly developed system that has the ability to discriminate blood flows at different tissue depths. Studies I and II explored blood flow responses at different depths in 17 individuals. In Study I the blood flow was related to tissue thickness and tissue compression during pressure exposure of ≥ 220 mmHg. In Study II, the sacral tissue was loaded with 37.5 mmHg and 50.0 mmHg, and the variation in blood flow was measured. Studies III and IV included 42 healthy individuals < 65 years, 38 healthy individuals ≥ 65 years, and 35 patients ≥ 65 years. Study III included between-subject comparisons of blood flow and pressure between individuals in the three study groups lying in supine positions on a standard hospital mattress. Study IV added within-subject comparisons while the individual was lying on four different types of mattress. The studies explored the vascular phenomena pressure-induced vasodilation (PIV) and reactive hyperemia (RH).The most common blood flow response to tissue exposure in this thesis was PIV, although a decrease in blood flow (a lack of PIV) was observed in some individuals. The patients tended to have higher interface pressure during pressure exposure than the healthy groups but no differences in blood flow responses were seen. Our results showed that pressure levels that are normally considered to be harmless could have a significant effect on the microcirculation in different tissue structures. Differences in individual blood flow responses in terms of PIV and RH were seen, and a larger proportion of individuals lacked these responses in the deeper tissue structures compared to more superficial tissue structures.This thesis identified PIV and RH that are important vascular mechanisms for pressure ulcer development and revealed for the first time that PIV and RH are present at different depths under clinically relevant conditions. The thesis also identified a population of individuals not previously identified who lack both PIV and RH and seem to be particularly vulnerable to pressure exposure. Further, this thesis has added a new perspective to the microcirculation in pressure ulcer etiology in terms of blood flow regulation and endothelial function that are anchored in clinically relevant studies. Finally, the evaluation of pressureredistribution support surfaces in terms of mean blood flow during and after tissue exposure was shown to be unfeasible, but the assessment of PIV and RH could provide a new possibility for measuring individual physiological responses that are known to be related to pressure ulcer development.
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| 2. |
- Ståhl, Patrik, Dr., et al.
(författare)
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Visualization and analysis of gene expression in tissue sections by spatial transcriptomics
- 2016
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Ingår i: Science. - : AMER ASSOC ADVANCEMENT SCIENCE. - 0036-8075 .- 1095-9203. ; 353:6294, s. 78-82
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Tidskriftsartikel (refereegranskat)abstract
- Analysis of the pattern of proteins or messenger RNAs (mRNAs) in histological tissue sections is a cornerstone in biomedical research and diagnostics. This typically involves the visualization of a few proteins or expressed genes at a time. We have devised a strategy, which we call "spatial transcriptomics," that allows visualization and quantitative analysis of the transcriptome with spatial resolution in individual tissue sections. By positioning histological sections on arrayed reverse transcription primers with unique positional barcodes, we demonstrate high-quality RNA-sequencing data with maintained two-dimensional positional information from the mouse brain and human breast cancer. Spatial transcriptomics provides quantitative gene expression data and visualization of the distribution of mRNAs within tissue sections and enables novel types of bioinformatics analyses, valuable in research and diagnostics.
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| 3. |
- Fredriksson, Camilla, 1969-
(författare)
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Keratinocytes in tissue engineering of human skin: invitro and in vivo studies
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Full thickness wounds, such as deep burns, need restoration of both the dermal and epidermal layers of the skin. In normal wound healing, re-epithelialization occurs by migration and proliferation of keratinocytes from the wound edges and by differentiation of stem cells from remaining hair follicles. Restoration of dermis occurs by influx of growth factors secreted by macrophages, platelets, and fibroblasts; by fibroblast proliferation and subsequent synthesis and remodeling of collagenous dermal matrix. In the case of full-thickness acute burn injuries and chronic wounds (e.g. pressure ulcers, venous ulcers and diabetic foot ulcers), these processes are defective. With the principles of tissue engineering in mind (to correct, improve and maintain tissues and their functions), researchers have developed promising materials and methods to make it possible to restore either the dermal (Integra® DRT, Alloderm®) or the epidermal layer (split thickness skin grafts (STSG), cultured epithelial autografts (CEA), autologous keratinocytes in single cell suspension). It is now well established that superior results are obtained if both dermal and epidermal components are combined, for example in a bilayered skin equivalent. Apligraf® is recommended for use on venous ulcers and is the only bilayered living skin equivalent currently approved by the FDA. Studies on different factors affecting the wound healing capacity as well as techniques in use provide valuable information for further development.In this licentiate thesis, we evaluated different transplantation techniques for delivering cultured human keratinocytes in single cell suspension, a measure becoming more frequently used in addition to STSG and CEA for restoring the epidermal layer of the skin. We found that the pressure device, commonly used to spray cell suspension onto the wound with pressures as high as 200 kPa, killed around 0% of the cells. In comparison, an ordinary syringe with the attachment of a spray nozzle showed almost 90% viable cells post transplantation and provided an equally good distribution of the cell suspension.We also studied different silver containing dressings regarding silver accumulation in human skin. In addition, we graded the re-epithelialization to evaluate whether the dressings caused any delay in the wound healing process. We found that the silver dressings tested, with few exceptions, caused dermal accumulation of silver, primarily aggregated around blood vessels. We could also show that most of the dressings had negative effect on the re-epithelialization.For the restoration of the dermal layer of the skin, Integra® DRT functions as a scaffold for guided tissue regeneration of the dermis. We had the possibility to study a case of necrotizing fasciitis were the treatment consisted of the use of Integra® DTR together with sub-atmospheric pressure (after initial surgical debridement) and later transplantation of split thickness skin grafts. This measure proved to be safe as well as giving satisfactory pliable and aesthetically acceptable result.
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| 4. |
- Nyman, Erika, 1976-
(författare)
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Guided Regeneration of the Human Skin : in vitro and in vivo studies
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Every day and in all parts of the world, humans experience different grades of wounding and tissue loss of the skin, thus initiating one of the most complex biological processes. Acute and chronic wounds, as well as the additional problem of skin scarring, involve not only great suffering for the patient but also extensive health care costs for the society. Although the wound-healing process is a wellstudied field much knowledge must be gained to unlock the door to regenerative pathways in humans.Epidermis heals by complete regeneration, but dermal and full thickness injuries heal with fibrosis and scar formation. In Papers I and II, we studied whether dermal scarring could be turned into regeneration by using two different types of threedimensional dermal scaffolds. In Paper I, we studied a solid scaffold made of poly(urethane urea), initially in vitro then followed by in vivo studies. In Paper II, we intradermally injected a liquid three-dimensional scaffold consisting of porous gelatin spheres in human healthy volunteers. Both materials showed ingrowth of functional fibroblasts and blood vessels and appeared to stimulate regeneration while slowly degrading. This finding could be of significant clinical importance, for example in burn wound care or after cancer surgery.In Papers III and IV, we wanted to study the effects of amniotic fluid and hyaluronic acid on adult wound healing, because early fetal wounds re-epithelialize rapidly and naturally heal dermis by regeneration without the need of a dermal scaffold. Amniotic fluid, naturally rich in hyaluronic acid, induced an accelerated reepithelialization of adult human wounds in vitro, and hyaluronic acid seemed to be important for this effect. Stimulation with exogenous hyaluronic acid in vivo induced accelerated re-epithelialization and an altered protein expression in healthy human volunteers. The inflammatory phase of wound healing, as measured by tissue viability imaging, was not affected by hyaluronic acid. Elucidating the effects of amniotic fluid and hyaluronic acid on the wound-healing process may allow improved treatment of wounds with impaired healing.Studies on finding new dermal scaffolds and studies on the positive effect of amniotic fluid or hyaluronic acid on the wound-healing process are two different ways of gaining insight that may lead to regeneration and improved wound healing for the patient.
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