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- 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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| 2. |
- Thorfinn, Johan, 1970-
(författare)
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Studies on sitting pressure and buttock microcirculation : aiming at developing an alarm in the prevention of pressure ulcers in patients with spinal cord injuries
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Pressure ulcers in patients with spinal cord injuries are a major problem, the prevalence in this group being reported as high as 20 – 30 percent. Most pressure ulcers develop around the pelvic girdle, and the key-contributing factor in the development of pressure ulcers is ischaemia due to longstanding pressure. Loss of mobility and lack of sensation below the level of injury are prominent risk factors for the development of pressure ulcers. Although many factors are known to contribute to pressure ulcer development, the exact aetiology is not completely clear. Prevention is suggested as the best way to deal with the problem. The studies in this thesis investigate some aspects of the physiology of sitting in patients with spinal cord injuries and healthy controls, aiming at developing a pressure ulcer alarm device to aid in the prevention of pressure ulcers. Methods used are laser Doppler perfusion imaging (LDPI) for measurement of superficial skin blood flow, as well microdialysis and a microelectrode (Licox®) to measure direct and indirect signs of ischaemia. In addition sitting pressures are mapped. The main findings are that patients with spinal cord injuries have almost four-fold mean maximum sitting pressures 43 and 49 N/cm2, left and right buttock) compared with healthy controls 12 and 13 N/cm2, left and right buttock). In the subcutaneous fat in healthy individuals, the tissue oxygen pressure decreases significantly during 30 minutes of sitting on a wheel chair cushion 13,7 mmHg) compared with 30 minutes of sitting on a hard surface 19,8 mmHg) implying that the tissues deep in the skin are exposed to a reduction in blood supply. This is also confirmed by a decrease in extracellular glucose during sitting for 30 minutes on a hard surface 1,8 mmol/L) and on a wheel chair cushion 1,7 mmol/L). The post-sitting reactive hyperaemia is dependent on duration of sitting in both patients and healthy subjects. It seems to be attenuated in patients in the sitting position but intensified while lying prone. Furthermore, four repeated loadings on a hard surface 15 minutes of sitting followed by five minutes of rest) without allowing the tissues to return to resting perfusion results in a significantly increasing reactive hyperaemia for each loading in healthy subjects, suggesting that it is important to unload the buttock skin completely before the next sitting period starts. This thesis also describes the construction of an alarm device that measures surface interface pressures during sitting continuously in eight predefined points, to alert the user by an audible signal after a given period of time when the pressure has reached a dangerously high level. It is concluded that the reactive hyperaemia that is observed in the buttock skin after sitting, as well as the reduction in glucose and oxygen in adipose tissue during sitting, are due to a reduction in blood supply relative or absolute ischaemia) caused by a compression of the vasculature by the ischial tuberosities. These findings imply a multilayer aetiology in pressure ulcer development. The altered hyperaemic reaction in patients with spinal cord injuries after sitting is possibly related to alterations in sympathetic activity due to the cord lesion. Lastly, the alarm device is supposed to be an aid to pressure ulcer prevention in patients with spinal cord injuries who lack normal sensory feedback.
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| 3. |
- Ivansson, Milena Edith, 1986-
(författare)
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Stable chlorine isotope analysis of chlorinated acetic acids
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Chlorinated acetic acids (CAAs) constitute a group of polar organic compounds that are ubiquitous in the environment. Their environmental occurrence has been extensively studied but their sources are still not well constrained. Isotopic characterization of compounds found in the environment can provide additional information and allow their source apportionment. Previous studies indicate, however, that CAAs of industrial and natural origin may not be distinguishable by stable carbon isotope analysis only. This thesis presents an analytical method for stable chlorine isotope analysis of CAAs using gas chromatography/quadruple mass spectrometry (GC/qMS), for which systems are found in most laboratories. The method was cross-calibrated with an offline reference method and allows the determination of chlorine isotope signatures of CAAs with sample amounts as small as 10 pmol with good precisions of <1 ‰. With this method CAAs can be isotopically characterized at environmental relevant concentrations, in contrast to conventional offline methods were large sample requirements limit the application. This new method enables multi-element stable isotope analysis of CAAs and may help to identify and quantify sources of CAAs to the environment.
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