| 1. |
- Bergkvist, Max, et al.
(författare)
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Assessment of microcirculation of the skin using Tissue Viability Imaging: A promising technique for detecting venous stasis in the skin
- 2015
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Ingår i: Microvascular Research. - : Elsevier. - 0026-2862 .- 1095-9319. ; 101, s. 20-25
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Tidskriftsartikel (refereegranskat)abstract
- Background: : Venous occlusion in the skin is difficult to detect by existing measurement techniques. Our aim was to find out whether Tissue Viability Imaging (TiVi) was better at detecting venous occlusion by comparing it with results of laser Doppler flowmetry (LDF) during graded arterial and venous stasis in human forearm skin. Methods: : Arterial and venous occlusions were simulated in 10 healthy volunteers by inflating a blood pressure cuff around the upper right arm. Changes in the concentration of red blood cells (RBC) were measured using TiVi, while skin perfusion and concentration of moving red blood cells (CMBC) were measured using static indices of LDF during exsanguination and subsequent arterial occlusion, postocclusive reactive hyperaemia, and graded increasing and decreasing venous stasis. Results: : During arterial occlusion there was a significant reduction in the mean concentration of RBC from baseline, as well as in perfusion and CMBC (p less than 0.008). Venous occlusion resulted in a significant 28% increase in the concentration of RBC (p = 0.002), but no significant change in perfusion (mean change -14%) while CMBC decreased significantly by 24% (p = 0.02). With stepwise increasing occlusion pressures there was a significant rise in the TiVi index and reduction in perfusion (p = 0.008), while the reverse was seen when venous flow was gradually restored. Conclusion: : The concentration of RBC measured with TiVi changes rapidly and consistently during both total and partial arterial and venous occlusions, while the changes in perfusion, measured by LDF, were less consistent This suggests that TiVi could be a more useful, non-invasive clinical monitoring tool for detecting venous stasis in the skin than LDF.
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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. |
- Bergkvist, Max, 1976-, et al.
(författare)
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Vascular Occlusion in a Porcine Flap Model : Effects on Blood Cell Concentration and Oxygenation.
- 2017
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Ingår i: Plastic and Reconstructive Surgery - Global Open. - : Wolters Kluwer. - 2169-7574. ; 5:11
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Tidskriftsartikel (refereegranskat)abstract
- Background: Venous congestion in skin flaps is difficult to detect. This study evaluated the ability of tissue viability imaging (TiVi) to measure changes in the concentration of red blood cells (CRBC), oxygenation, and heterogeneity during vascular provocations in a porcine fasciocutaneous flap model.Methods: In 5 pigs, cranial gluteal artery perforator flaps were raised (8 flaps in 5 pigs). The arterial and venous blood flow was monitored with ultrasonic flow probes. CRBC, tissue oxygenation, and heterogeneity in the skin were monitored with TiVi during baseline, 50% and 100% venous occlusion, recovery, 100% arterial occlusion and final recovery, thereby simulating venous and arterial occlusion of a free fasciocutaneous flap. A laser Doppler probe was used as a reference for microvascular perfusion in the flap.Results: During partial and complete venous occlusion, increases in CRBC were seen in different regions of the flap. They were more pronounced in the distal part. During complete arterial occlusion, CRBC decreased in all but the most distal parts of the flap. There were also increases in tissue oxygenation and heterogeneity during venous occlusion.Conclusions: TiVi measures regional changes in CRBC in the skin of the flap during arterial and venous occlusion, as well as an increase in oxygenated hemoglobin during venous occlusion that may be the result of reduced metabolism and impaired delivery of oxygen to the tissue. TiVi may provide a promising method for measuring flap viability because it is hand-held, easy to-use, and provides spatial information on venous congestion.
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| 4. |
- Droog Tesselaar, Erik, 1977-, et al.
(författare)
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Changes in skin microcirculation during radiation therapy for breast cancer
- 2017
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Ingår i: Acta Oncologica. - Oxfordshire : Taylor & Francis. - 0284-186X .- 1651-226X. ; 56:8, s. 1072-1080
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The majority of breast cancer patients who receive radiation treatment are affected by acute radiation-induced skin changes. The assessment of these changes is usually done by subjective methods, which complicates the comparison between different treatments or patient groups. This study investigates the feasibility of new robust methods for monitoring skin microcirculation to objectively assess and quantify acute skin reactions during radiation treatment.MATERIAL AND METHODS: Laser Doppler flowmetry, laser speckle contrast imaging, and polarized light spectroscopy imaging were used to measure radiation-induced changes in microvascular perfusion and red blood cell concentration (RBC) in the skin of 15 patients undergoing adjuvant radiation therapy for breast cancer. Measurements were made before treatment, once a week during treatment, and directly after the last fraction.RESULTS: In the treated breast, perfusion and RBC concentration were increased after 1-5 fractions (2.66-13.3 Gy) compared to baseline. The largest effects were seen in the areola and the medial area. No changes in perfusion and RBC concentration were seen in the untreated breast. In contrast, Radiation Therapy Oncology Group (RTOG) scores were increased only after 2 weeks of treatment, which demonstrates the potential of the proposed methods for early assessment of skin changes. Also, there was a moderate to good correlation between the perfusion (r = 0.52) and RBC concentration (r = 0.59) and the RTOG score given a week later.CONCLUSION: We conclude that radiation-induced microvascular changes in the skin can be objectively measured using novel camera-based techniques before visual changes in the skin are apparent. Objective measurement of microvascular changes in the skin may be valuable in the comparison of skin reactions between different radiation treatments and possibly in predicting acute skin effects at an earlier stage.
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| 5. |
- Elawa, Sherif, et al.
(författare)
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The microvascular response in the skin to topical application of methyl nicotinate : Effect of concentration and variation between skin sites
- 2019
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Ingår i: Microvascular Research. - : Academic Press. - 0026-2862 .- 1095-9319. ; 124, s. 54-60
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundMethyl nicotinate (MN) induces a local cutaneous erythema in the skin and may be used as a local provocation in the assessment of microcirculation and skin viability. The aims were to measure the effects of increasing doses of MN, to find the concentration that yields the most reproducible effect from day to day and between sites, and to study the variation between skin sites.MethodsMicrovascular responses to topically applied MN at different concentrations were measured in 12 subjects on separate days and on contralateral sides, using laserspeckle contrast imaging (LSCI). MN effects were measured in four different body sites.ResultsAt 20 mmol/L, the response to MN was most reproducible day-to-day and site-to-site, and resulted in a plateau response between 5 and 20 min after application.The skin region of the lower back had a lower perfusion value compared to the epigastric region (p = 0.007). When responses were compared to nearby, unprovoked areas, a significantly larger increase in perfusion was seen in the forearm, compared to all other anatomical sites (p < 0.03).ConclusionA concentration of 20 mmol/L MN generated the most reproducible microvascular response in the skin. The response varies between different body sites.
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| 6. |
- Elmasry, Moustafa, 1981-, et al.
(författare)
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Laser speckle contrast imaging in children with scalds : Its influence on timing of intervention, duration of healing and care, and costs
- 2019
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Ingår i: Burns. - : Elsevier. - 0305-4179 .- 1879-1409. ; 45:4, s. 798-804
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundScalds are the most common type of burn injury in children, and the initial evaluation of burn depth is a problem. Early identification of deep dermal areas that need excision and grafting would save unnecessary visits and stays in hospital. Laser speckle contrast imaging (LSCI) shows promise for the evaluation of this type of burn. The aim of this study was to find out whether perfusion measured with LSCI has an influence on the decision for operation, duration of healing and care period, and costs, in children with scalds.MethodsWe studied a group of children with scalds whose wounds were evaluated with LSCI on day 3–4 after injury during the period 2012–2015. Regression (adjustment for percentage total body surface area burned (TBSA%), age, and sex) was used to analyse the significance of associations between degree of perfusion and clinical outcome.ResultsWe studied 33 children with a mean TBSA% of 6.0 (95% CI 4.4–7.7)%. Lower perfusion values were associated with operation (area under the receiver-operating characteristic curve 0.86, 95% CI 0.73–1.00). The perfusion cut-off with 100% specificity for not undergoing an operation was ≥191 PU units (66.7% sensitivity and 72.7% accurately classified). Multivariable analyses showed that perfusion was independently associated with duration of healing and care period.ConclusionLower perfusion values, as measured with LSCI, are associated with longer healing time and longer care period. By earlier identification of burns that will be operated, perfusion measurements may further decrease the duration of care of burns in children with scalds.
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| 7. |
- Ericsson, Elin, et al.
(författare)
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Effect of Electrode Belt and Body Positions on Regional Pulmonary Ventilation- and Perfusion-Related Impedance Changes Measured by Electric Impedance Tomography
- 2016
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Ingår i: PLOS ONE. - : PUBLIC LIBRARY SCIENCE. - 1932-6203. ; 11:6, s. e0155913-
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Tidskriftsartikel (refereegranskat)abstract
- Ventilator-induced or ventilator-associated lung injury (VILI/VALI) is common and there is an increasing demand for a tool that can optimize ventilator settings. Electrical impedance tomography (EIT) can detect changes in impedance caused by pulmonary ventilation and perfusion, but the effect of changes in the position of the body and in the placing of the electrode belt on the impedance signal have not to our knowledge been thoroughly evaluated. We therefore studied ventilation-related and perfusion-related changes in impedance during spontaneous breathing in 10 healthy subjects in five different body positions and with the electrode belt placed at three different thoracic positions using a 32-electrode EIT system. We found differences between regions of interest that could be attributed to changes in the position of the body, and differences in impedance amplitudes when the position of the electrode belt was changed. Ventilation-related changes in impedance could therefore be related to changes in the position of both the body and the electrode belt. Perfusion-related changes in impedance were probably related to the interference of major vessels. While these findings give us some insight into the sources of variation in impedance signals as a result of changes in the positions of both the body and the electrode belt, further studies on the origin of the perfusion-related impedance signal are needed to improve EIT further as a tool for the monitoring of pulmonary ventilation and perfusion.
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| 8. |
- Iredahl, Fredrik, 1988-
(författare)
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Assessment of microvascular and metabolic responses in the skin
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The general aim of this project was to develop experimental in vivo models that allow for minimally invasive investigations of responses in the skin to microvascular and metabolic provocations. The cutaneous microvasculature has emerged as a valuable model and been proposed to mirror the microcirculation in other organs. Dysfunction in the cutaneous microcirculation has thus been linked to systemic diseases such as hypertension and diabetes mellitus. Models for investigating skin responses could facilitate the understanding of pathophysiological mechanisms as well as effects of drugs.In the first study, three optical measurement techniques (laser Doppler flowmetry (LDF), laser speckle contrast imaging (LSCI) and tissue viability imaging (TiVi)) were compared against each other and showed differences in their ability to detect microvascular responses to provocations in the skin. TiVi was found more sensitive for measurement of noradrenaline-induced vasoconstriction, while LSCI was more sensitive for measurement of vascular occlusion. In the second study, microvascular responses in the skin to iontophoresis of vasoactive drugs were found to depend on the drug delivery protocol. Perfusion half-life was defined and used to describe the decay in the microvascular response to a drug after iontophoresis. In the third study, the role of nitric oxide (NO) was assessed during iontophoresis of insulin. The results showed a NO-dependent vasodilation in the skin by insulin. In the fourth study the vasoactive and metabolic effects of insulin were studied after both local and endogenous administration. Local delivery of insulin increased skin blood flow, paralleled by increased skin concentrations of interstitial pyruvate and lactate, although no change in glucose concentration was observed. An oral glucose load resulted in an increased insulin concentration in the skin paralleled by an increase in blood flow, as measured using the microdialysis urea clearance technique, although no changes in perfusion was measured by LSCI.The thesis concludes that when studying skin microvascular responses, the choice of measurement technique and the drug delivery protocol has an impact on the measurement results, and should therefore be carefully considered. The thesis also concludes that insulin has metabolic and vasodilatory effects in the skin both when administered locally and as an endogenous response to an oral glucose load. The vasodilatory effect of insulin in the skin is mediated by nitric oxide.
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| 9. |
- Iredahl, Fredrik, et al.
(författare)
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Modeling Perfusion Dynamics in the Skin During Iontophoresis of Vasoactive Drugs Using Single-Pulse and Multiple-Pulse Protocols
- 2015
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Ingår i: Microcirculation. - : Informa Healthcare / Wiley: 12 months. - 1073-9688 .- 1549-8719. ; 22:6, s. 446-453
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Tidskriftsartikel (refereegranskat)abstract
- Objective: After iontophoresis of vasoactive drugs into the skin, a decrease in perfusion is commonly observed. We delivered vasoactive drugs by iontophoresis using different delivery protocols to study how these affect this decrease in perfusion as measured using LDF. Methods: We measured skin perfusion during iontophoresis of (ACh), MCh, andNAusing a single pulse or separate pulses at different skin sites, and during repeated delivery of ACh at the same site. Results: Perfusion half-life was 6.1 (5.6-6.6) minutes for ACh and 41 (29-69) minutes for MCh (p less than 0.001). The maximum response with multiple pulses of ACh iontophoresis was lower than with a single pulse, 30 (22-37) PU vs. 43 (36-50) PU, p less than 0.001. Vasoconstriction to NA was more rapid with a single pulse than with multiple pulses. The perfusion half-life of ACh decreased with repeated delivery of ACh at the same site-first 16 (14-18), second 5.9 (5.1-6-9) and third 3.2 (2.9-3.5) minutes, p less than 0.001. Conclusions: The drug delivery protocol affects microvascular responses to iontophoresis, possibly as a result of differences in the dynamics of local drug concentrations. Perfusion half-life may be used as a measure to quantify the rate of perfusion recovery after iontophoresis of vasoactive drugs.
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| 10. |
- Iredahl, Fredrik, et al.
(författare)
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Non-Invasive Measurement of Skin Microvascular Response during Pharmacological and Physiological Provocations
- 2015
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Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 10:8, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- Introduction Microvascular changes in the skin due to pharmacological and physiological provocations can be used as a marker for vascular function. While laser Doppler flowmetry (LDF) has been used extensively for measurement of skin microvascular responses, Laser Speckle Contrast Imaging (LSCI) and Tissue Viability Imaging (TiVi) are novel imaging techniques. TiVi measures red blood cell concentration, while LDF and LSCI measure perfusion. Therefore, the aim of this study was to compare responses to provocations in the skin using these different techniques. Method Changes in skin microcirculation were measured in healthy subjects during (1) iontophoresis of sodium nitroprusside (SNP) and noradrenaline (NA), (2) local heating and (3) post-occlusive reactive hyperemia (PORH) using LDF, LSCI and TiVi. Results Iontophoresis of SNP increased perfusion (LSCI: baseline 40.9 +/- 6.2 PU; 10-min 100 +/- 25 PU; pless than0.001) and RBC concentration (TiVi: baseline 119 +/- 18; 10-min 150 +/- 41 AU; p = 0.011). No change in perfusion (LSCI) was observed after iontophoresis of NA (baseline 38.0 +/- 4.4 PU; 10-min 38.9 +/- 5.0 PU; p = 0.64), while RBC concentration decreased (TiVi: baseline 59.6 +/- 11.8 AU; 10-min 54.4 +/- 13.3 AU; p = 0.021). Local heating increased perfusion (LDF: baseline 8.8 +/- 3.6 PU; max 112 +/- 55 PU; pless than0.001, LSCI: baseline 50.8 +/- 8.0 PU; max 151 +/- 22 PU; pless than0.001) and RBC concentration (TiVi: baseline 49.2 +/- 32.9 AU; max 99.3 +/- 28.3 AU; pless than0.001). After 5 minutes of forearm occlusion with prior exsanguination, a decrease was seen in perfusion (LDF: p = 0.027; LSCI: pless than0.001) and in RBC concentration (p = 0.045). Only LSCI showed a significant decrease in perfusion after 5 minutes of occlusion without prior exsanguination (pless than0.001). Coefficients of variation were lower for LSCI and TiVi compared to LDF for most responses. Conclusion LSCI is more sensitive than TiVi for measuring microvascular changes during SNP-induced vasodilatation and forearm occlusion. TiVi is more sensitive to noradrenaline-induced vasoconstriction. LSCI and TiVi show lower inter-subject variability than LDF. These findings are important to consider when choosing measurement techniques for studying skin microvascular responses.
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