| 1. |
- Högstedt, Alexandra, 1993-
(författare)
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Microvascular effects of insulin in the skin
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The microcirculation in the skin is essential for skin homeostasis. In instances of altered microvascular function, that may be the result of insulin resistance, tissue morbidity may ensue. The underlying mechanisms are however complex and not fully understood. By studying the physiological effects of insulin in the skin, the understanding of the complex interplay between glucose metabolism and skin microcirculation can be improved. The general aim of this thesis was to develop an experimental in vivo model to study metabolic and microvascular responses to insulin in the skin in healthy subjects. Microdialysis is a suiting technique as it allows for both local delivery of drugs and simultaneous monitoring of the local metabolic and vascular effects in the very same tissue compartment. The effects of local and systemic insulin provocation on skin blood flow and metabolism were investigated using microdialysis urea clearance and laser speckle contrast imaging (paper I). An insulin dependent increase in skin blood flow was observed, presumably induced through the nitric oxide pathway (paper II). Investigating the protein expression during an oral glucose provocation using proteomic approaches however indicates interactions with other pathways, such as the renin-angiotensin system and the kallikrein-kinin system (paper IV). Paper III also investigated methodological concerns regarding the sampling of insulin using microdialysis. This in vivo model can, in the future, be applied to assess the microvascular effects of insulin in the skin in different patient groups, including those with micro-vascular dysfunction due to, for instance, insulin resistance.
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| 2. |
- Bergkvist, Max, 1976-
(författare)
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Studies on Polarised Light Spectroscopy
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis project focuses on measurements of dermal microcirculation during vascular provocations with polarised light spectroscopy. This is done with a non-invasive method commercially available as Tissue viability imaging (TiVi) which measures concentration and oxygenation of red blood cells in the papillary dermis. Three studies were done with human subjects and one with an animal model, to validate and compare the TiVi technique with laser Doppler flowmetry, which is an established method of measuring dermal microcirculation.The TiVi consists of a digital camera with polarisation filters in front of the flash and lens, with software for analysis of the picture. When taking a picture with the TiVi, the polarised light that is reflected on the skin surface is absorbed by the second filter over the lens (which is perpendicular to the first filter) but a portion of light penetrates the surface of the skin and is scattered when it is reflected on tissue components. This makes the light depolarised, passes the second filter, and produces a picture for analysis. The red blood cell (RBC) has a distinct absorption pattern that differs between red and green colour compared to melanin and other components of tissue. This difference is used by the software that calculates differences in each picture element and produces a measure of output which is proportional to the concentration of red blood cells. The oxygenation of RBC can also be calculated, as there is a difference in absorption depending on oxygen state.The first paper takes up possible sources of error such as ambient light, and the angle and distance of the camera. The main experiment was to investigate how the local heating reaction is detected with TiVi compared to LDF.In the second paper arterial and venous stasis are examined in healthy subjects with TiVi.The Third paper is an animal study where skin flaps were raised on pigs, and the vascular pedicle is isolated to enable control of inflow and outflow of blood.The measurements were made during partial venous, total venous, and total arterial occlusion. The TiVi recorded changes in the concentration of RBC, oxygenation and heterogeneity and the results were compared with those of laser Doppler flowmetry.In the fourth paper oxygenation and deoxygenation of RBC: s was studied. Studies were made on the forearms of healthy subjects who were exposed to arterial and venous occlusion. Simultaneous measurements were made with TiVi and Enhanced perfusion and oxygen saturation or EPOS, which is a new device that combines laser Doppler flowmetry and diffuse reflectance spectroscopy in one probe.With TiVi, one can measure RBC concentration and oxygenation in the area of an entire picture or in one or multiple user defined regions of interest (ROI). Methods such as laser Doppler flowmetry makes single point measurements, which is a potential source of error both because of the heterogeneity of the microcirculation, and that the circulation be insufficient in the margins of the investigated area. TiVi has been able to measure venous stasis more accurately than laser Doppler flowmetry, and venous stasis is the more common reason for flaps to fail.The TiVi is an accurate way to measure the concentration of RBC and trends in oxygenation of the dermal microcirculation. It has interesting possible applications for microvascular and dermatological research, monitoring of flaps, and diagnosis of peripheral vascular disease. Future clinical studies are needed as well as development of the user interface.
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| 3. |
- Zdolsek, Markus, 1989-
(författare)
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Volume effects of albumin infusion in humans
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: The use of colloids when treating a patient for hypovolemia has been debated throughout the years. During the last decade, albumin solutions have become the colloids of choice in both operating theatres and intensive care settings when crystalloid fluids are insufficient. The volume effects of albumin infusion are explored in this thesis. Methods: Recruitment of fluid from the interstitial fluid compartment to the plasma was estimated in healthy volunteers who received 3 ml/kg of albumin 20% infusion over 30 min. The same infusion protocol was applied to burn patients to study whether significant inflammation changes the volume effect of an albumin infusion. The influence of the infusion rate of albumin 20% on plasma volume (PV) was evaluated in a crossover fashion in healthy volunteers. Additionally, two concentrations, 5% and 20%, with equivalent amounts of albumin, were given to healthy volunteers in a crossover fashion to determine if a difference in volume effect occurred. The volume effects in terms of PV expansion and capillary leakage of albumin were calculated by mass balance and volume kinetics based on repeated blood samples. Results: There was a 10–20 min delay after completion of the albumin 20% infusion until maximum PV expansion was reached. Extravascular fluid was recruited at a ratio of 3.4 times the infused albumin 20%. Both healthy volunteers and burn patients had a 15% increase in PV. Capillary leakage of albumin occurred at a similar rate in both groups. Rapid infusion resulted in a longer intravascular half-life for albumin and a larger initial PV expansion over time without long-term negative compensation. Albumin 20% increased the PV to twice the infused volume in contrast to albumin 5%, which only increased the PV by two-thirds of the infused volume. Conclusion: Albumin infusions provide long-lasting PV expansion in both burn patients and healthy volunteers. Albumin 20% induces the recruitment of extravascular fluid, amounting to three times the infused fluid volume. A rapid infusion rate is beneficial, as it results in a larger initial PV expansion over time and a longer intravascular persistence of albumin. Further, albumin 20% provides a three times more potent PV expansion than albumin 5%. The infused fluid volume of an albumin solution depends more on the amount of albumin infused than the infused volume; albumin 20% could be preferred over other fluids for its dehydrating effect in the prevention of oedema.
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| 4. |
- Zötterman, Johan, 1975-
(författare)
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Laser Speckle Contrast Imaging in Reconstructive Surgery
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- ObjectivesReconstructive surgery aims to restore function or normal appearance by reconstructing defective organs after trauma or disease. In patients undergoing reconstructive surgery, previous trauma, surgery or radiotherapy can result in compromised blood supply. This will affect the viability of the tissue and increases the risk for postoperative complications, such as ischemia and infection. It is therefore important to assess the tissue viability, both before, during and after the surgery. This can be done using different techniques that monitor the perfusion of the skin covering the affected area. In this thesis, LSCI have been evaluated for tissue monitoring in reconstructive surgery. The technique allows for a fast and noninvasive assessment of superficial tissue perfusion over a wide field. Based on previous work on the technology, we have seen clear advantages with LSCI compared to other methods, for example laser Doppler flowmetry (LDF). We have evaluated laser speckle contrast imaging (LSCI) as a tool for tissue monitoring in reconstructive surgery in four studies.MethodsIn study I we used a bench top model and healthy subjects to address methodological concerns subjected to the LSCI technology. We investigated the effect of motion distance and angle on the assessed perfusion value In study II we used a porcine model to compare LSCI and LDF as tools to detect partial and full venous outflow obstruction. We used both methods to assess a flap based on the cranial gluteal artery perforator with partial and complete occlusion of the vein and artery. In study III we used the same porcine model as in study II to investigate the possibility to use LSCI intraoperatively to identify flap areas with compromised circulation and thereby predict areas with a high risk of postoperative necrosis. In study IV we used LSCI for intraoperative evaluation of tissue viability during deep inferior epigastric perforator (DIEP) free flap surgery and to investigate the perfusion distribution according to the Hartrampf zones, as measured with LSCI, in relation to the selected perforator in the deep inferior epigastric perforator free flap.ResultsIn study I we saw that tissue perfusion as measured with LSCI increases with increasing tissue motion, independent of frame rate, number of images, and tissue perfusion. Measured perfusion will decrease when images are acquired at an angle larger than 45° but distances between 15 and 40 cm do not affect the measured perfusion. In study II we observed significant decreases in perfusion during both partial and complete venous occlusion with both LSCI and LDF. However, higher variability seen with LDF, measured as % coefficient of variation. In study III a decrease in perfusion during the first 30 min after raising the flap and a perfusion value below 25 PU after 30 min was a predictor for tissue morbidity 72h after surgery. In study IV the highest perfusion values were found in zone I and higher perfusion in zone II compared to zone III, directly after the flap was raised. No remaining significant difference between zone I, II and III could be seen after anastomosis of the vessels. All flaps with a minimum perfusion <30 PU, measured after the flap was shaped and inserted, later suffered from partial flap necrosis.ConclusionLSCI is a technology that has the potential to contribute to tissue monitoring in reconstructive surgery. It has many advantages over other techniques, such as the fast acquisition time, the spatial resolution and the fact that it is completely non-invasive. However, the current system is still too bulky to be easily introduced into a clinical setting and the technology is also subject to certain drawbacks which limit its usability. It is sensitive to motion artefacts; only superficial tissue is assessed and cannot offer absolute perfusion data. If these disadvantages could be addressed, LSCI could contribute to a more accurate survey of tissue perfusion and thus better outcome in reconstructive surgery.
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| 5. |
- Elawa, Sherif, 1988-
(författare)
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Microvascular Function Assessment after Mastectomy and Radiation Therapy in Breast Cancer Patients : From Methodology to Clinical Application
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Post-mastectomy radiotherapy (PMRT) is an important part of the treatment of breast cancer. It reduces the risk of recurrence and improves overall survival. Scaring and fibrotization of the skin and subcutaneous tissue of the chest wall or remaining breast are among its side-effects. These late side-effects of PMRT may in turn affect skin microcirculation and oxygenation, although this connection is not completely established. In patients that later require breast reconstruction, it is difficult as a plastic surgeon to evaluate if the microcirculatory changes have been affected by PMRT, and how such effects should have an impact on the choice of reconstructive method. In the work presented in this thesis, laser speckle contrast imaging (LSCI), laser-doppler flowmetry (LDF) and diffuse reflectance spectroscopy (DRS) have been used with a strong vasodilator, methyl nicotinate (MN) to study the microcirculatory changes after PMRT.In studies I and II, we aimed to find the optimal concentration of MN and its main mechanisms of action. In healthy volunteers, the microvascular response to different concentrations of MN was evaluated on the forearm using LSCI. It was found that a concentration of 20 mmol/l resulted in a quick vasodilatory response with a long plateau phase, minimal tissue edema and no non-responders. In study II, we utilized locally administered drugs to block the three main pathways responsible for skin vasodilation. Subsequently, we provoked the skin with MN and assessed its effect with LSCI. From this study we could conclude that MN’s mechanism of action is largely mediated by prostaglandins and partly by local sensory nerves.In study III, we examined the skin microcirculatory response in breast cancer patients before, immediately after, and at two and six months following unilateral PMRT, using the contralateral breast as a control. A significant increase in basal skin perfusion and perfusion after application of MN was observed on the irradiated chest wall immediately after RT compared to the contralateral breast and compared to before RT. At six months after RT, there was no longer a difference in basal skin perfusion or after application of MN in the irradiated chest wall compared to the contralateral breast and compared to before RT was given. The results from this study concluded that skin perfusion in the irradiated chest wall had returned to normal when measured six months after RT.In study IV, the late effects on skin microvascular function were studied in women who had undergone mastectomy and PMRT several years prior to the study. Skin perfusion and oxygen saturation was measured with white light diffuse reflectance spectroscopy (DRS) combined with Laser Doppler Flowmetry (LDF) before and after application of MN on the irradiated chest wall with the contralateral non-irradiated breast as control. In this study we found that skin perfusion and oxygenation in the breast are affected several years after radiotherapy and that our method could be a valuable clinical tool prior to deciding surgical procedures after PMRT.To conclude, MN can be topically applied to the skin to reliably assess microvascular function and the microvascular capacity. LSCI and LDF have different strengths and drawbacks, with LSCI having the advantage of having a large spatial resolution that allows for measurements of control areas in the same field of view as the provoked areas. LDF in combination with DRS enabled us to further assess perfusion and oxygenation simultaneously which could be an advantage in fibrotic skin where skin perfusion and oxygen saturation may not correlate with each other. Although the study groups differed between the study examining the early effects of PMRT with the late effects of PMRT, we have been able to non-invasively visualize changes in microcirculation in relation to the acute and chronic phase after PMRT. Future studies are needed to investigate the value of pre-operative measurements with MN provocation for predicting surgical outcome.
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| 6. |
- Mirdell, Robin, 1989-
(författare)
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Blood Flow Dynamics in Burns
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Objectives:Burns of intermediate thickness are hard to evaluate clinically. This often leads to unnecessary delays of up to 14 days before a surgical decision can be made. To counter this, several objective methods have been developed to determine the healing potential of the wound. Over the years, measurement of perfusion has proven to be the most successful method for evaluation of healing potential. Laser Doppler imaging (LDI) is currently the most used method and can determine surgical need 2 days after injury with an accuracy >90%. There are however emerging techniques like laser speckle contrast imaging (LSCI), which also measure perfusion. LSCI have several advantages over LDI and is easier to use. LSCI can also investigate aspects of the microcirculation, previously not possible with LDI. The aim of this thesis was to investigate LSCI’s ability to evaluate surgical need in burns of indeterminate partial-thickness. The first objective was to investigate the dynamics of perfusion the first 14 days after injury. The purpose was to find the optimal time-window for perfusion measurements. The next goal was to determine the accuracy of different perfusion cut-offs. In this second study, the benefit of a subsequent measurement was also investigated. After this, interobserver variation between different profession groups was studied. Both the agreement of perfusion measurements and observer assessments were evaluated. Finally, cardiac vasomotion in combination with perfusion (pulsatility) was investigated as a method to determine surgical need <48 hours after injury. Methods:Perfusion was measured in a total of 77 patients at the Department of Plastic Surgery, Hand Surgery and Burns at Linköping University Hospital, Sweden. Most of these patients were children and the most common type of burn was scalds. A laser speckle contrast imager (PeriCam PSI System, Perimed AB, Järfälla, Sweden) was used to measure perfusion. Results: In the first paper we showed a clear relation between perfusion dynamics and the healing potential of the wound. The changes in perfusion were largest the first 5 days after injury, why this time interval was selected for subsequent papers. Perfusion measurements done day 3-4 after injury could predict surgical need with a sensitivity of 100% (95% CI: 83.9-100%) and a specificity of 90.4% (95% CI: 83.8-94.9%). If two measurements were used, <24 hours and 3-4 days after injury, the accuracy was 100%. Furthermore, we found that different observers could consistently predict perfusion, while there was a large variation in their clinical assessments. This was not improved by extensive burn experience. Finally, pulsatility could be used to predict surgical need the same day as the injury occurred with a sensitivity of 100% (95% CI: 88.1-100%) and a specificity of 98.8% (95% CI: 95.7- 99.9%). Conclusions: LSCI is a promising method for evaluation of burns and provides several benefits over LDI. The surgical need of burns can be determined mere hours after injury when pulsatility is measured. However, the benefits of early scald diagnostics in children with LSCI need to be evaluated in a prospective study before the method is ready for routine clinical use.
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| 7. |
- Moloney, Maria
(författare)
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Ulnar fractures and ligament injuries of the wrist
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Falling over on an outstretched hand with the wrist extended is a common accident that can cause a multitude of injuries in the wrist. Research has mainly focused on distal radius fractures while injuries of the distal ulna and adjacent ligaments have taken a back seat. If not treated adequately, these injuries may result in ulnar-sided wrist pain, sometimes referred to as the “black box” of hand surgery. The distal radio-ulnar joint (DRUJ) enables forearm rotation where the radio-carpal unit rotates around the fixed ulna, stabilised most importantly by the triangular fibrocartilage complex (TFCC). Painless rotation and stability of the forearm under load is important for upper limb function. If full function is to be restored after wrist injury, it is important to treat not only injury to the radius but also those to the ulna and TFCC.The aims of this thesis were to evaluate the long-term results of TFCC injury repair, and contribute to our knowledge on fractures of the distal ulna, their epidemiology, radiographic classification and results of treatment.The long-term outcome of 47 patients with a foveal TFCC tear was evaluated by patient-rated wrist evaluation (PRWE) and radiography 20 years after open repair. The median PRWE score was 22.6 (7-48.5), and 34 % had had further surgery after the initial repair, half of these due to recurrence of DRUJ instability. Signs of osteoarthritis were seen in the radiocarpal joint in 17.5 % and in the DRUJ in 34 %. Higher PRWE scores were seen in patients with osteoarthritis or those who had undergone further surgery. Radio-carpal osteoarthritis was less frequently seen in patients who had undergone initial arthroscopy. This study highlights the importance of arthroscopy in identifying associated injuries. Twenty years after foveal TFCC tear repair patient reported outcomes were similar to those of distal radius fractures.Apart from fractures of the styloid process, distal ulna fractures are rare. All distal ulna fractures in the county of Östergötland 2010-2012 were identified. A total of 766 fractures were found (incidence 74/100 000 person-years), the majority of which were fractures of the ulnar styloid process(79%) usually caused by a fall from standing height. Most patients were female (76%), mean age at the time of injury was 63 years and 92 % had a concomitant distal radius fracture. Second after styloid fractures were fractures of the ulnar neck. A retrospective study of 96 patients with 97 fractures of the distal ulna (excluding the styloid) showed that 40 % were treated by internal fixation. The median PRWE score was 15, with significantly worse scores in patients with an internally fixed distal ulna fracture compared to patients not operated. When classifying these fractures according to AO/OTA 2018, transverse extra-articular fractures (2U3A2.3) had a significantly better outcome when not treated surgically, and these probably do not require internal fixation if the distal radius provides stability and alignment. All 97 fractures were classified by three independent observers according to three classification systems: Biyani, AO/OTA 2007, and AO/OTA 2018. Classification was repeated after a minimum of 3 weeks. Reliability and reproducibility were calculated. The reliability was judged as fair for AO/OTA 2007, and moderate for Biyani and AO/OTA 2018. The reproducibility was moderate for all three systems. These results together with the observers´ opinion that Biyani is an easier system to use, leads us to conclude that a slightly modified Biyani-system together with improved radiological techniques that provide more information about the fracture pattern, may well improve accuracy, reliability and reproducibility.A better classification of distal ulna fractures could help us in the evaluation of new and existing treatments as well as providing the information necessary for designing treatment algorithm. After careful consideration, internal fixation is probably the treatment of choice for certain types of fracture, but this needs further investigation.
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| 8. |
- Farnebo, Simon, 1972-
(författare)
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On microvascular blood flow assessment with the new microdialysis urea clearance technique
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis was to develop and evaluate a new way of monitoring blood flow with microdialysis. A thin catheter consisting of a semipermeable membrane is implanted in the tissue being studied. The catheter is perfused by a solution that closely resembles interstitial fluid, and small water-soluble substances are allowed to diffuse passively through the pores of the membrane with the aim at reaching equilibrium with the surrounding tissue. The minimally invasive character of microdialysis, and its ability to sample from the organ being studied, make microdialysis attractive in most research settings as well as for clinical surveillance. It has, however, become increasingly evident that microdialysis under conditions of non-equilibrium - for example, fluctuating regional blood flow, will alter the results gained. We have therefore aimed to explore the possibilities of developing a new marker of blood flow that will yield information about changes in blood flow that occur in the area of the microdialysis catheter itself.We hypothesised that the changes in the diffusion of exogenous urea could be used as markers of changes in tissue blood flow. The theoretical basis for this approach is that the mass transfer of urea will increase across the dialysis membrane secondary to increased blood flow. As removal of urea from the vicinity of the dialysis membrane increases with increased blood flow, the concentration gradient of urea between the perfusate and tissue will also increase. This in turn will result in a greater loss of urea from the perfusate. The changes noted in retrieval of urea from dialysate by the system are therefore thought to be inversely related to changes in blood flow. We tested our hypothesis in two species of animal (rat and pig) and in man, and in three organ systems (muscle, liver, and skin), and present four papers that indicate that the urea clearance technique provides reliable and reproducible results. The technique was evaluated against conventional metabolic markers (lactate and glucose), the ethanol clearance technique (microdialysis), laser Doppler perfusion imaging (LDPI), and polarisation light spectroscopy (TiVi).We present evidence that the urea clearance technique can be used to assess blood flow in the organs studied reliably and reproducibly with microdialysis. The microdialysis technique is minimally invasive and safe for the recipient, and catheters can easily be implanted during operation to monitor organs at risk. Urea is easily analysed as a standard assay among other “basic” metabolic markers (in a standard microdialysis kit) and has favourable characteristics with a standardised measurement system that is routinely used for monitoring metabolites in the clinic. The technique is also effective when used at lower perfusate flow rates (<1 μl/minute), which is advantageous as the recovery of metabolic markers increases at low perfusate flow rates.
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