| 1. |
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| 2. |
- Henricson, Joakim, et al.
(författare)
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Local Heating as a Predilatation Method for Measurement of Vasoconstrictor Responses with Laser-Doppler Flowmetry
- 2011
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Ingår i: Microcirculation. - : John Wiley & Sons. - 1073-9688 .- 1549-8719. ; 18:3, s. 214-220
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Tidskriftsartikel (refereegranskat)abstract
- Studying microvascular responses to iontophoresis of vasoconstricting drugs contributes to a better understanding of the regulatory mechanisms of cutaneous vessels, but measuring these responses with laser-Doppler flowmetry at basal blood flow conditions is technically challenging. This study aimed to investigate whether the measurement of cutaneous vasoconstrictor responses to noradrenaline (NA) and phenylephrine (PE), delivered by iontophoresis, is facilitated by predilatation of the microvascular bed using local heating. We used different drug delivery rates (100 s x 0.12 mA, 200 s x 0.06 mA, 300 s x 0.04 mA) to investigate whether predilatation affects the local drug dynamics by an increased removal of drugs from the skin. In a predilatated vascular bed, iontophoresis of NA and PE resulted in a significant decrease in perfusion from the thermal plateau (p andlt; 0.001). The decrease was 25-33%, depending on drug delivery rate. In unheated skin, a significant vasoconstriction was observed (p andlt; 0.001), with 17% and 14% decrease from baseline for NA and PE, respectively. These results indicate that predilatating the cutaneous vascular bed by local heating facilitates measurement of vasoconstriction with laser-Doppler flowmetry and does not seem to significantly affect the result by an increased removal of drugs from the skin.
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| 3. |
- Bergstrand, Sara, et al.
(författare)
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Existence of Tissue Blood Flow in Response to External Pressure in the Sacral Region of Elderly Individuals - Using an Optical Probe Prototype
- 2010
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Ingår i: MICROCIRCULATION. - : Taylor and Francis. - 1073-9688 .- 1549-8719. ; 17:4, s. 311-319
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Tidskriftsartikel (refereegranskat)abstract
- Pandgt;Objective: The aim was to investigate the existence of sacral tissue blood flow at different depths in response to external pressure and compression in elderly individuals using a newly developed optical probe prototype. Methods: The tissue blood flow and tissue thickness in the sacral area were measured during load in 17 individuals using laser Doppler flowmetry and photoplethysmography in a combined probe, and digital ultrasound. Results: The mean age was 68.6 +/- 7.0 years. While loading, the mean compression was 60.3 +/- 11.9%. The number of participants with existing blood flow while loading increased with increased measurement depth. None had enclosed blood flow deep in the tissue and at the same time an existing more superficial blood flow. Correlation between tissue thickness and BMI in unloaded and loaded sacral tissue was shown: r = 0.68 (P = 0.003) and r = 0.68 (P = 0.003). Conclusions: Sacral tissue is highly compressed by external load. There seems to be a difference in responses to load in the different tissue layers, as occluded blood flow in deeper tissue layers do not occur unless the blood flow in the superficial tissue layers is occluded.
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| 4. |
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| 5. |
- Farnebo, Simon, 1972-, et al.
(författare)
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Assessment of blood flow changes in human skin by microdialysis urea clearance
- 2011
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Ingår i: Microcirculation. - : Wiley. - 1073-9688 .- 1549-8719. ; 18:3, s. 198-204
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Forskningsöversikt (refereegranskat)abstract
- Objective: The aim of this study was to evaluate the urea clearance technique for the measurement of drug-induced blood flow changes in human skin, and compare it with two non-invasive techniques: polarization light spectroscopy and laser Doppler perfusion imaging. Methods: Fifteen microdialysis catheters were placed intracutaneously on the volar aspect of the forearms of healthy human subjects, and were perfused with nitroglycerine, noradrenaline, and again nitroglycerine, to induce local tissue hyperaemia, hypoperfusion, and hyperaemia, respectively. Results: Urea clearance, but not the other techniques, detected the changes in blood flow during all three periods of altered flow. The last hyperaemic response was detected by all three methods. Conclusion: Urea clearance can be used as a relatively simple method to estimate blood flow changes during microdialysis of vasoactive substances, in particular when the tissue is preconditioned in order to enhance the contrast between baseline and the responses to the provocations. Our results support that, in the model described, urea clearance was superior to the optical methods as it detected both the increases and decrease in blood flow, and the returns to baseline between these periods.
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| 6. |
- Mellor, Russell H, et al.
(författare)
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Lymphatic dysfunction, not aplasia, underlies Milroy disease.
- 2010
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Ingår i: Microcirculation. - : Wiley. - 1073-9688 .- 1549-8719. ; 17:4
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: Milroy disease is an inherited autosomal dominant lymphoedema caused by mutations in the gene for vascular endothelial growth factor receptor-3 (VEGFR-3, also known as FLT4). The phenotype has to date been ascribed to lymphatic aplasia. We further investigated the structural and functional defects underlying the phenotype in humans.METHODS: The skin of the swollen foot and the non-swollen forearm was examined by (i) fluorescence microlymphangiography, to quantify functional initial lymphatic density in vivo; and (ii) podoplanin and LYVE-1 immunohistochemistry of biopsies, to quantify structural lymphatic density. Leg vein function was assessed by colour Doppler duplex ultrasound.RESULTS: Milroy patients exhibited profound (86-91%) functional failure of the initial lymphatics in the foot; the forearm was unimpaired. Dermal lymphatics were present in biopsies but density was reduced by 51-61% (foot) and 26-33% (forearm). Saphenous venous reflux was present in 9/10 individuals with VEGFR3 mutations, including two carriers.CONCLUSION: We propose that VEGFR3 mutations in humans cause lymphoedema through a failure of tissue protein and fluid absorption. This is due to a profound functional failure of initial lymphatics and is not explained by microlymphatic hypoplasia alone. The superficial venous valve reflux indicates the dual role of VEGFR-3 in lymphatic and venous development.
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| 7. |
- Tchou Folkesson, Kim, et al.
(författare)
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A Human Vascular Model Based on Microdialysis for the Assessment of the Vasoconstrictive Dose-Response Effects of Norepinephrine and Vasopressin in Skin
- 2012
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Ingår i: Microcirculation. - : Informa Healthcare / John Wiley and Sons. - 1073-9688 .- 1549-8719. ; 19:4, s. 352-359
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Tidskriftsartikel (refereegranskat)abstract
- Abstract Objective: Microdialysis enables drug delivery in the skin and simultaneous measurement of their effects. The present study aimed to evaluate dose-dependent changes in blood flow and metabolism during microdialysis of norepinephrine and vasopressin. Methods: We investigated whether increasing concentrations of norepinephrine (NE, 1.859 mu mol/L) and vasopressin (VP, 1100 nmol/L), delivered sequentially in one catheter or simultaneously through four catheters, yield dose-dependent changes in blood flow (as measured using urea clearance) and metabolism (glucose and lactate). Results: We found a significant dose-dependent vasoconstriction with both drugs. Responses were characterized by a sigmoid dose response model. Urea in the dialysate increased from a baseline of 7.9 +/- 1.7 to 10.9 +/- 0.9 mmol/L for the highest concentration of NE (p andlt; 0.001) and from 8.1 +/- 1.4 to 10.0 +/- 1.7 mmol/L for the highest concentration of VP (p = 0.037). Glucose decreased from 2.3 +/- 0.7 to 0.41 +/- 0.18 mmol/L for NE (p = 0.001) and from 2.7 +/- 0.6 to 1.3 +/- 0.5 mmol/L for VP (p andlt; 0.001). Lactate increased from 1.1 +/- 0.4 to 2.6 +/- 0.5 mmol/L for NE (p = 0.005) and from 1.1 +/- 0.4 to 2.6 +/- 0.5 mmol/L for VP (p = 0.008). There were no significant differences between responses from a single catheter and from those obtained simultaneously using multiple catheters. Conclusions: Microdialysis in the skin, either with a single catheter or using multiple catheters, offers a useful tool for studying dose response effects of vasoactive drugs on local blood flow and metabolism without inducing any systemic effects.
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| 8. |
- Tesselaar, Erik, et al.
(författare)
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Polarized Light Spectroscopy for Measurement of the Microvascular Response to Local Heating at Multiple Skin Sites
- 2012
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Ingår i: Microcirculation. - : Informa Healthcare / John Wiley and Sons. - 1073-9688 .- 1549-8719. ; 19:8, s. 705-713
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Tidskriftsartikel (refereegranskat)abstract
- Objective: To evaluate whether TiVi, a technique based on polarized light, could measure the change in RBC concentration during local heating in healthy volunteers. Methods: Using a custom-made transparent heater, forearm skin was heated to 42 degrees C for 40 minutes while the change in RBC concentration was measured with TiVi. The perfusion response during local heating was measured at the same time with Laser Doppler flowmetry. Results: Mean RBC concentration increased (91 +/- 34 vs. 51 +/- 34 A.U. at baseline, p less than 0.001). The spatial heterogeneity of the RBC concentration in the measured skin areas was 26 +/- 6.4% at baseline, and 23 +/- 4.6% after 40 minutes of heating. The mean RBC concentrations in two skin sites were highly correlated (0.98 at baseline and 0.96 after 40 minutes of heating). The change in RBC concentration was less than the change in perfusion, measured with LDF. Unlike with LDF, a neurally mediated peak was not observed with TiVi in most of the test subjects. Conclusions: TiVi is a valuable technique for measuring the microvascular response to local heating in the skin, and offers a high reproducibility for simultaneous measurements at different skin sites, provided carefully controlled experiments are ensured.
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| 9. |
- Albinsson, Sebastian, et al.
(författare)
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Stretch-dependent smooth muscledifferentiation in theportal vein - role of actin polymerization, calcium signaling and microRNAs.
- 2014
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Ingår i: Microcirculation. - : Wiley. - 1549-8719 .- 1073-9688. ; 21:3, s. 230-238
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Forskningsöversikt (refereegranskat)abstract
- The mechanical forces acting onsmooth muscle cells in the vascular wall are known to regulate processes such as vascular remodeling and contractile differentiation. However, investigations to elucidate the underlying mechanisms of mechanotransduction in smooth muscle have been hampered by technical limitations associated with mechanical studies on pressurized small arteries, due primarily to the small amount of available tissue. The murine portal vein is a relatively large vessel showing myogenic tone that in many respects recapitulates the properties of small resistance vessels. Studies on stretched portal veins to elucidate mechanisms of mechanotransduction in the vascular wall have shown that stretch-sensitive regulation of contractile differentiation is mediated via Rho-activation and actin polymerization, while stretch-induced growth is regulated by the MAP-kinase pathway. In this review, we have summarized findings on mechanotransduction in the portal vein with focus on stretch-induced contractile differentiation and the role of calcium, actin polymerization and microRNAs in this response. This article is protected by copyright. All rights reserved.
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| 10. |
- Bergstrand, Sara, et al.
(författare)
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Pressure-induced vasodilation and reactive hyperemia at different depths in sacral tissue under clinically relevant conditions
- 2014
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Ingår i: Microcirculation. - : John Wiley & Sons. - 1073-9688 .- 1549-8719. ; 21:8, s. 761-771
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: To characterize pressure-induced vasodilatation and reactive hyperemia at different sacral tissue depths in different populations under clinically relevant pressure exposure.METHODS: Forty-two subjects (< 65 years), 38 subjects (≥ 65 years), and 35 patients (≥ 65 years) participated. Interface pressure, skin temperature, and blood flow at tissue depths of 1 mm, 2 mm, and 10 mm (using laser Doppler flowmetry and photoplethysmography) were measured in the sacral tissue before, during, and after load in a supine position.RESULTS: pressure-induced vasodilatation and reactive hyperemia were observed at three tissue depths. At 10 mm depth, the proportion of subjects with a lack of pressure-induced vasodilatation was higher compared to superficial depths. The patients had higher interface pressure during load than the healthy individuals, but there were no significant differences in blood flow. Twenty-nine subjects in all three study groups were identified with a lack of pressure-induced vasodilatation and reactive hyperemia.CONCLUSIONS: pressure-induced vasodilatation and reactive hyperemia can be measured at different tissue depths. A lack of these responses was found in healthy individuals as well as in patients indicating an innate susceptibility in some individuals, and are potential important factors to evaluate in order to better understand the etiology of pressure ulcers.
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| 11. |
- Bergstrand, Sara, et al.
(författare)
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The relationship between forearm skin speed-resolved perfusion and oxygen saturation, and finger arterial pulsation amplitudes, as indirect measures of endothelial function
- 2018
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Ingår i: Microcirculation. - : WILEY. - 1073-9688 .- 1549-8719. ; 25:2
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Endothelial function is important for regulating peripheral blood flow to meet varying metabolic demands and can be measured indirectly during vascular provocations. In this study, we compared the PAT finger response (EndoPAT) after a 5-minutes arterial occlusion to that from forearm skin comprehensive microcirculation analysis (EPOS). Methods: Measurements in 16 subjects with varying cardiovascular risk factors were carried out concurrently with both methods during arterial occlusion, while forearm skin was also evaluated during local heating. Results: Peak values for EPOS skin Perf(conv) and speed-resolved total perfusion after the release of the occlusion were significantly correlated to the EndoPAT RHI (rho =.68, P = .007 and rho =.60, P = .025, respectively), mainly due to high-speed blood flow. During local heating, EPOS skin oxygen saturation, SO2, was significantly correlated to RHI (rho = .62, P =.043). This indicates that SO2 may have diagnostic value regarding endothelial function. Conclusions: We have demonstrated for the first time a significant relationship between forearm skin microcirculatory perfusion and oxygen saturation and finger PAT. Both local heating and reactive hyperemia are useful skin provocations. Further studies are needed to understand the precise regulation mechanisms of blood flow and oxygenation during these tests.
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| 12. |
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| 13. |
- Högstedt, Alexandra, et al.
(författare)
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Effect of N-G-monomethyl l-arginine on microvascular blood flow and glucose metabolism after an oral glucose load
- 2020
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Ingår i: Microcirculation. - : WILEY. - 1073-9688 .- 1549-8719. ; 27:3
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Tidskriftsartikel (refereegranskat)abstract
- Objective The aim of this study was to investigate whether the effects on local blood flow and metabolic changes observed in the skin after an endogenous systemic increase in insulin are mediated by the endothelial nitric oxide pathway, by administering the nitric oxide synthase inhibitor N-G-monomethyl l-arginine using microdialysis. Methods Microdialysis catheters, perfused with N-G-monomethyl l-arginine and with a control solution, were inserted intracutaneously in 12 human subjects, who received an oral glucose load to induce a systemic hyperinsulinemia. During microdialysis, the local blood flow was measured by urea clearance and by laser speckle contrast imaging, and glucose metabolites were measured. Results After oral glucose intake, microvascular blood flow and glucose metabolism were both significantly suppressed in the N-G-monomethyl l-arginine catheter compared to the control catheter (urea clearance: P amp;lt; .006, glucose dialysate concentration: P amp;lt; .035). No significant effect of N-G-monomethyl l-arginine on microvascular blood flow was observed with laser speckle contrast imaging (P = .81). Conclusion Local delivery of N-G-monomethyl l-arginine to the skin by microdialysis reduces microvascular blood flow and glucose delivery in the skin after oral glucose intake, presumably by decreasing local insulin-mediated vasodilation.
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| 14. |
- 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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| 15. |
- Iredahl, Fredrik, et al.
(författare)
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Skin glucose metabolism and microvascular blood flow during local insulin delivery and after an oral glucose load
- 2016
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Ingår i: Microcirculation. - : Wiley-Blackwell. - 1073-9688 .- 1549-8719. ; 23:7, s. 597-605
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: Insulin causes capillary recruitment in muscle and adipose tissue, but the metabolic and microvascular effects of insulin in the skin have not been studied in detail. The aim of this study was to measure glucose metabolism and microvascular blood flow in the skin during local insulin delivery and after an oral glucose load.METHODS: Microdialysis catheters were inserted intracutanously in human subjects. In eight subjects two microdialysis catheters were inserted, one perfused with insulin and one with control solution. First the local effects of insulin was studied, followed by a systemic provocation by an oral glucose load. Additionally, as control experiment, six subjects did not recieve local delivery of insulin or the oral glucose load. During microdialysis the local blood flow was measured by urea clearance and by laser speckle contrast imaging (LSCI).RESULTS: Within 15 minutes of local insulin delivery, microvascular blood flow in the skin increased (urea clearance: P=.047, LSCI: P=.002) paralleled by increases in pyruvate (P=.01) and lactate (P=.04), indicating an increase in glucose uptake. An oral glucose load increased urea clearance from the catheters, indicating an increase in skin perfusion, although no perfusion changes were detected with LSCI. The concentration of glucose, pyruvate and lactate increased in the skin after the oral glucose load.CONCLUSION: Insulin has metabolic and vasodilatory effects in the skin both when given locally and after systemic delivery through an oral glucose load.
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| 16. |
- Iredahl, Fredrik, et al.
(författare)
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The Microvascular Response to Transdermal Iontophoresis of Insulin is Mediated by Nitric Oxide
- 2013
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Ingår i: Microcirculation. - : WILEY-BLACKWELL, 111 RIVER ST, HOBOKEN 07030-5774, NJ USA. - 1073-9688 .- 1549-8719. ; 20:8, s. 717-723
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Tidskriftsartikel (refereegranskat)abstract
- ObjectiveInsulin has direct effects on blood flow in various tissues, most likely due to endothelial NO production. We investigated whether insulin delivered to the skin by iontophoresis increases microvascular perfusion and whether this effect is partly or completely mediated by the release of NO. MethodsIn healthy subjects, regular insulin and monomeric insulin were delivered to the skin by cathodal iontophoresis. The skin was pretreated either with L-NAME or control solution (PBS) using anodal iontophoresis. Microvascular responses were measured using laser Doppler flowmetry. ResultsA dose-dependent increase in perfusion was observed during iontophoresis of regular and monomeric insulin. The maximum perfusion was significantly elevated compared with control after PBS (regular insulin 53.6 (12.7-95.6) PU vs. 4.2 (3.4-4.8) PU, p = 0.002; monomeric insulin 32.6 (8.9-92.6) PU vs. 5.9 (3.4-56.0) PU, p = 0.03). The microvascular response to insulin was abolished after L-NAME (regular insulin: 25.6 (11.6-54.4) PU vs. control: 4.7 (2.9-11.5) PU, p = 0.15; monomeric insulin 10.9 (5.4-56.8) PU vs. control: 4.7 (2.9-11.5) PU, p = 0.22). ConclusionsThe main finding is that iontophoresis of insulin induces a dose-dependent vasodilation in the skin, which could be suppressed after pretreatment with a NO synthase inhibitor. This suggests that vasodilation in the skin after iontophoresis of insulin is mediated by the NO pathway.
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| 17. |
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| 18. |
- Källman, Ulrika, et al.
(författare)
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Blood flow responses over sacrum in nursing home residents during one hour bed rest
- 2016
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Ingår i: Microcirculation. - : WILEY-BLACKWELL. - 1073-9688 .- 1549-8719. ; 23:7, s. 530-539
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Tidskriftsartikel (refereegranskat)abstract
- ObjectivesTo describe individual BF responses in a nursing home resident population for one-hour periods of bed rest. MethodsBF was measured for one hour over the sacrum in 0 degrees supine position and 30 degrees supine tilt position in 25 individuals aged 65 y or older while lying on a pressure-redistributing mattress. Measurements were made at three tissue depths (1, 2, and 10 mm) using the noninvasive optical techniques, LDF and PPG. ResultsEleven participants had a PIV response at 1mm depth in both positions and seven participants had a lack of this response at this depth and positions. The BF response at 1mm depth appeared immediately and remained over, or below, baseline for the entire 60min of loading in both positions. These BF patterns were also seen in deeper tissue layers. ConclusionsThe cutaneous BF response among the nursing home residents was distinct, appeared early, and remained during the one hour of loading.
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| 19. |
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| 20. |
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| 21. |
- Sundheim, Liv Kristin, et al.
(författare)
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Acute skin trauma induces hyperemia, but superficial papillary nutritive perfusion remains unchanged
- 2017
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Ingår i: Microcirculation. - : WILEY. - 1073-9688 .- 1549-8719. ; 24:7
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Tidskriftsartikel (refereegranskat)abstract
- Objectives: Superficial skin papillary capillaries with blood supply from a superficial vascular plexus and regulated by local metabolic needs supply oxygen and nutrients for epithelial cell proliferation. A deep vascular plexus regulated by autonomous nerves serves body thermoregulation. In healthy volunteers, we assessed circulatory effects of a standardized skin trauma by CAVM, DRS, and LDPM to assess the measuring depth of the three techniques and to describe the acute trauma effects on nutritive and thermoregulatory perfusion. Methods: Volunteers (n=12) were examined at baseline and after induction of a 5.0 mmx1.0 mm incision on the forearm; 30 minutes after the trauma induction, data were collected at 0-1, 2-3 and 30 mm distances. Results: LDPM showed hyperemia at 2-3 mm distance (35.8 +/- 15.2 a.u.), but not at 30 mm distance (7.4 +/- 2.5 a.u.) compared to baseline (8.8 +/- 1.8 a.u.). The DRS saturation increased at 2-3 mm (71.2 +/- 4.8%), but not at 30 mm (49.8 +/- 7.9%) compared to baseline (45.8 +/- 7.4%). Capillary density and flow velocities were unaffected at all distances. Conclusions: The results indicate that skin nutritive papillary capillary function can be assessed by CAVM and DRS, but not with LDPM because of its dependence of the deep plexus perfusion.
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| 22. |
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| 23. |
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| 24. |
- Edvinsson, Marie-Louise, et al.
(författare)
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Characterization of Relaxant Responses to Natriuretic Peptides in the Human Microcirculation In Vitro and In Vivo
- 2016
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Ingår i: Microcirculation. - : Wiley. - 1073-9688. ; 23:6, s. 438-446
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Tidskriftsartikel (refereegranskat)abstract
- Objective: We characterized the vasodilatory effects of ANP, BNP, and CNP in human subcutaneous arterioles in vitro and the cutaneous microcirculation in vivo. Methods: The in vitro experiments were performed using wire myography and the responses were characterized by the use of inhibitors for nitric oxide (L-NAME), prostaglandin synthesis (indomethacin), or the endothelium-derived hyperpolarization factor. In vivo, the vasorelaxant effect of iontophoretically administrated BNP or CNP was measured with a noninvasive laser Doppler technique. Involvement of nitric oxide or prostaglandins was assessed by L-NAME or indomethacin given by iontophoresis. Results: In vitro all three peptides showed significant vasodilatation with the efficacy order: CNP > BNP = ANP. The BNP-induced vasodilatation, but not that of ANP or CNP, was significantly reduced by pretreatment with indomethacin or L-NAME. In vivo administration of BNP induced a marked vasodilatory response that was attenuated by local pretreatment of L-NAME. Indomethacin by itself resulted in increased cutaneous perfusion. Conclusions: NPs are potent vasodilators in the human subcutaneous circulation. The response to BNP differs from that of the other peptides as it seems dependent on cyclooxygenase products and nitric oxide.
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| 25. |
- Rippe, Bengt, et al.
(författare)
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The peritoneal microcirculation in peritoneal dialysis
- 2001
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Ingår i: Microcirculation. - 1549-8719. ; 8:5, s. 303-320
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Forskningsöversikt (refereegranskat)abstract
- This paper deals with the peritoneal microcirculation and with peritoneal exchange occurring in peritoneal dialysis (PD). The capillary wall is a major barrier to solute and water exchange across the peritoneal membrane. There is a bimodal size-selectivity of solute transport between blood and the peritoneal cavity, through pores of radius approximately 40-50 A as well as through a very low number of large pores of radius approximately 250 A. Furthermore, during glucose-induced osmosis during PD, nearly 40% of the total osmotic water flow occurs through molecular water channels, termed "aquaporin-1." This causes an inequality between 1 - sigma and the sieving coefficient for small solutes, which is a key feature of the "three-pore model" of peritoneal transport. The peritoneal interstitium, coupled in series with the capillary walls, markedly modifies small-solute transport and makes large-solute transport asymmetric. Thus, although severely restricted in the blood-to-peritoneal direction, the absorption of large solutes from the peritoneal cavity occurs at a high clearance rate ( approximately 1 mL/min), largely independent of molecular radius. True absorption of macromolecules to the blood via lymphatics, however, seems to be occurring at a rate of approximately 0.2 mL/min. Several controversial issues regarding transcapillary and transperitoneal exchange mechanisms are discussed in this paper.
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| 26. |
- Ritsvall, Olivia, et al.
(författare)
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Emerging role of YAP/TAZ in vascular mechanotransduction and disease
- 2023
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Ingår i: Microcirculation. - 1073-9688.
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Forskningsöversikt (refereegranskat)abstract
- Cells have an incredible ability to physically interact with neighboring cells and their environment. They can detect and respond to mechanical forces by converting mechanical stimuli into biochemical signals in a process known as mechanotransduction. This is a key process for the adaption of vascular smooth muscle and endothelial cells to altered flow and pressure conditions. Mechanical stimuli, referring to a physical force exerted on cells, are primarily sensed by transmembrane proteins and the actin cytoskeleton, which initiate a cascade of intracellular events, including the activation of signaling pathways, ion channels, and transcriptional regulators. Recent work has highlighted an important role of the transcriptional coactivators YAP/TAZ for mechanotransduction in vascular cells. Interestingly, the activity of YAP/TAZ decreases with age, providing a potential mechanism for the detrimental effects of aging in the vascular wall. In this review, we summarize the current knowledge on the functional role of YAP and TAZ in vascular endothelial and smooth muscle cells for mechanotransduction in homeostasis and disease. In particular, the review is focused on in vivo observations from conditional knockout (KO) models of YAP/TAZ and the potential implications these studies may have for our understanding of vascular disease development.
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| 27. |
- Venturoli, Daniele, et al.
(författare)
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Estimation of in vivo pulmonary microvascular and interstitial geometry using digital image analysis
- 1995
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Ingår i: Microcirculation. - 1549-8719. ; 2:1, s. 27-40
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: To determine microvascular diameter and perivascular interstitium thickness at the lung surface in the in situ, in vivo lung. METHODS: Microscopic images of the lung surface collected through a "pleural window" by a videocamera were digitized with a monochrome frame grabber (512 x 512 pixels, 8 bits per pixels) to be computer analyzed by image processing techniques. RESULTS: We found that the maxima in the distribution of the standard deviations of gray levels in adjacent neighbors 7 x 7 pixels wide identify the edges between the microvessel lumen and the surrounding perivascular interstitium. Furthermore, the maxima in the distribution of the standard deviation of the standard deviations of gray levels identify the edges between the perivascular interstitium and the lung tissue. CONCLUSIONS: This technique can be applied to microvessels ranging in diameter from 30 microns to 200 microns and perivascular interstitial thickness of the order of 10-150 microns. Our approach allows for the definition of microvascular geometry even for noisy images and represents an improvement compared to other edge detection methods. The proposed analytical procedure may provide a useful tool to study lung fluid balance and microvascular reactivity in the in situ lung in the normal state and in response to a variety of functional conditions.
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