Robust analysis of microcirculatory flowmotion during post-occlusive reactive hyperemia.

BACKGROUND: Flowmotion analysis of the microcirculatory blood flow is a method to extract information about the vessel regulatory function. It has previously shown promise when applied to measurements during a post-occlusive reactive hyperemia. The reperfusion peak and the following monotonic decline introduces false low frequencies that should not be interpreted as rhythmic vasomotion effect. AIM: To develop and validate a robust method for flowmotion analysis of post-occlusive reactive hyperemia signals. METHOD: The occlusion-induced reperfusion response contains a typical rapid increase followed by a monotonic decline to baseline. A mathematical model is proposed to detrend this transient part of the signal to enable further flowmotion analysis. The model is validated in 96 measurements on healthy volunteers. RESULTS: Applying the proposed model corrects the flowmotion signal without adding any substantial new false flowmotion components. CONCLUSION: Future studies should use the proposed method or equivalent when analyzing flowmotion during post-occlusive reactive hyperemia to ensure valid results.

Sense of coherence, mental health, and hair cortisol concentrations among older people during the COVID -19 pandemic: a cross-sectional study.

BACKGROUND: A person's sense of coherence (SoC) is likely to affect coping when exposed to a life changing event like the COVID -19 pandemic, which impacted the older population especially hard, an age group that already suffers from a lot of mental illness. Thus, the aim of this study was to investigate the associations between SoC and mental health in older adults using both screening scales and hair cortisol concentrations (HCC). METHOD: A cross-sectional design studying a cohort of 70-80 years old, N = 260, set in Swedish primary care during the pandemic years 2021-2022. Instruments used are sense of coherence 13 (SoC-13), EQ-5D-3L, Geriatric depression scale 20 (GDS-20), Hospital anxiety and depression scale (HADS), and Perceived stress scale 10 (PSS-10). Sociodemography and factors concerning SoC, and mental health are explored. HCC are measured using radioimmunoassay. Outcome measures are factors independently associated with SoC. Linear regression models were performed with SoC as dependent variable, and priory path analyses explored whether associations with SoC were direct, or indirect via anxiety. RESULTS: SoC was significantly associated with anxiety (p < 0.001), perceived economic status (p = 0.003), belief in the future (p = 0.001), and perceived negative mental effect from the COVID -19 pandemic (p = 0.002). The latter was 96% indirectly associated with SoC (p < 0.001), whereas perceived economic status together with belief in the future was 82% directly associated with SoC (p = 0.17). HCC and sex were not significantly associated with SoC, but, noticeably, high HCC was equally distributed between women and men. Women reported significantly lower quality of life (p = 0.03), and more symptoms of anxiety (p = 0.001) and depression (p < 0.001). CONCLUSION: Anxiety, belief in the future, perceived negative effect on mental health due to the pandemic, and perceived economic status were significantly associated with SoC. Anxiety is suggested to be important in explaining the association between perceived negative mental effect from the COVID-19 pandemic and SoC. Women reported significantly poorer mental health and life quality than men.

Factors affecting self-perceived mental health in the general older population during the COVID-19 pandemic: a cross-sectional study.

BACKGROUND: Mental health problems among older people are large public health concerns but often go unrecognized and undertreated. During COVID - 19 several restrictions regarding social contacts were launched, primarily for the old. The objective of this study is to investigate which factors that had the main negative affect on mental health in the older population during the pandemic. METHOD: A cross-sectional cohort study set in Swedish primary care during the pandemic years 2021-2022. The population constitutes of 70-80-years-old, N = 260. Instruments used are Geriatric depression scale 20 (GDS20); Hospital anxiety and depression scale (HADS), and Perceived stress scale 10 (PSS10). Sociodemography and risk factors are explored. Outcome measures are factors independently associated with decreased mental health. Analyses were performed for the group as a whole and with logistic regression models comparing individuals who stated they were mentally affected by the pandemic to individuals who stated they were not. RESULTS: Participants who stated they were mentally affected by the COVID - 19 pandemic reported significantly higher levels of anxiety (p < 0.001), depression (p < 0.001), and stress (p = 0.026) compared to those who stated they were not mentally affected. Explanatory regression models of up to 50% showed that following factors were prominent among individuals who reported a decline in their mental health due to the COVID - 19 pandemic (n = 24); impaired social life (OR 20.29, p < 0.001, CI 4.53-90.81), change in physical activity (OR 5.28, p = 0.01, CI 1.49-18.72), perceived family situation (OR 31.90, p = 0,007, CI 2,53-402.42), mild/moderate and high anxiety (OR 4.94, p = 0.034, CI 1.13-21.60, OR 7.96, p = 0.035, CI 1.16-54.53 respectively), and female gender (OR 6.52, p = 0.029, CI 1.22-34.92). CONCLUSION: Anxiety, family situation, social life and change in physical activity were the main factors influencing the 70-80-years-old's self-perceived mental health during the COVID - 19 pandemic. Long-term effects of social restrictions on mental health in the older population need to be further investigated.

Workload and sex effects in comprehensive assessment of cutaneous microcirculation.

INTRODUCTION: Workload and sex-related differences have been proposed as factors of importance when evaluating the microcirculation. Simultaneous assessments with diffuse reflectance spectroscopy (DRS) and laser Doppler flowmetry (LDF) enable a comprehensive evaluation of the microcirculation. The aim of the study was to compare the response between sexes in the microcirculatory parameters red blood cell (RBC) tissue fraction, RBC oxygen saturation, average vessel diameter, and speed-resolved perfusion during baseline, cycling, and recovery, respectively. METHODS: In 24 healthy participants (aged 20 to 30 years, 12 females), cutaneous microcirculation was assessed by LDF and DRS at baseline, during a workload generated by cycling at 75 to 80 % of maximal age-predicted heart rate, and recovery, respectively. RESULTS: Females had significantly lower RBC tissue fraction and total perfusion in forearm skin microcirculation at all phases (baseline, workload, and recovery). All microvascular parameters increased significantly during cycling, most evident in RBC oxygen saturation (34 % increase on average) and perfusion (9-fold increase in total perfusion). For perfusion, the highest speeds (>10 mm/s) increased by a factor of 31, whereas the lowest speeds (<1 mm/s) increased by a factor of 2. CONCLUSION: Compared to a resting state, all studied microcirculation measures increased during cycling. For perfusion, this was mainly due to increased speed, and only to a minor extent due to increased RBC tissue fraction. Skin microcirculatory differences between sexes were seen in RBC concentration and total perfusion.

In vivo dose-response analysis to acetylcholine: pharmacodynamic assessment by polarized reflectance spectroscopy.

Transdermal iontophoresis offers an in vivo alternative to the strain-gauge model for measurement of vascular function but is limited due to lack of technical solutions for outcome assessment. The aims of this study were to, after measurement by polarized reflectance spectroscopy (PRS), use pharmacodynamic dose-response analysis on responses to different concentrations of acetylcholine (ACh); and to examine the effect of three consecutively administered iontophoretic current pulses. The vascular responses in 15 healthy volunteers to iontophorised ACh (5 concentrations, range 0.0001% to 1%, three consecutive pulses of 0.02 mA for 10 min each) were recorded using PRS. Data were fitted to a four-parameter logistic dose response model and compared. Vascular responses were quantifiable by PRS. Similar pharmacodynamic dose response curves could be generated irrespectively of the ACh concentration. Linearly increasing maximum vasodilatory responses were registered with increasing concentration of ACh. A limited linear dose effect of the concentration of ACh was seen between pulses. Polarized reflectance spectroscopy is well suited for measuring vascular responses to iontophoretically administrated ACh. The results of this study support further development of iontophoresis as a method to study vascular function and pharmacological responses in vivo.

Local Response and Barrier Recovery in Elderly Skin Following the Application of High-Density Microarray Patches.

The high-density microneedle array patch (HD-MAP) is a promising alternative vaccine delivery system device with broad application in disease, including SARS-CoV-2. Skin reactivity to HD-MAP applications has been extensively studied in young individuals, but not in the >65 years population, a risk group often requiring higher dose vaccines to produce protective immune responses. The primary aims of the present study were to characterise local inflammatory responses and barrier recovery to HD-MAPs in elderly skin. In twelve volunteers aged 69−84 years, HD-MAPs were applied to the forearm and deltoid regions. Measurements of transepidermal water loss (TEWL), dielectric permittivity and erythema were performed before and after HD-MAP application at t = 10 min, 30 min, 48 h, and 7 days. At all sites, TEWL (barrier damage), dielectric permittivity (superficial water);, and erythema measurements rapidly increased after HD-MAP application. After 7 days, the mean measures had recovered toward pre-application values. The fact that the degree and chronology of skin reactivity and recovery after HD-MAP was similar in elderly skin to that previously reported in younger adults suggests that the reactivity basis for physical immune enhancement observed in younger adults will also be achievable in the older population.

Micropuncture closure following high density microarray patch application in healthy subjects.

BACKGROUND: The high-density microarray patch (HD-MAP) promises to be a robust vaccination platform with clear advantages for future global societal demands for health care management. The method of action has its base not only in efficient delivery of vaccine but also in the reliable induction of a local innate physical inflammatory response to adjuvant the vaccination process. The application process needs to induce levels of reactivity, which are acceptable to the vaccine, and from which the skin promptly recovers. MATERIALS AND METHODS: 1 × 1 cm HD-MAP patches containing 5000, 250-µm long microprojections were applied to the skin in 12 healthy volunteers. The return of skin barrier function was assessed by transepidermal water loss (TEWL) and reaction to topical histamine challenge. RESULTS: Skin barrier recovery by 48 h was confirmed for all HD-MAP sites by recovered resistance to the effects of topical histamine application. CONCLUSIONS: Our previous observation, that the barrier disruption indicator TEWL returns to normal by 48 h, is supported by this paper's demonstration of return of skin resistance to topical histamine challenge in twelve healthy subjects.

Low awareness of non-alcoholic fatty liver disease in patients with type 2 diabetes in Swedish Primary Health Care.

OBJECTIVES: Non-alcoholic fatty liver disease (NAFLD) is more common in patients with type 2 diabetes mellitus (T2DM) compared to individuals without. Recent guidelines recommend screening for NAFLD in patients with T2DM. Our aim was to investigate the prevalence of NAFLD in patients with T2DM in a Swedish primary health care setting, how they are cared for and assess the risk of biochemical signs of advanced fibrosis. MATERIAL AND METHODS: In this cohort study, patients with T2DM from five primary health care centers were included. Medical records were retrospectively reviewed and living habits, medical history, results of diagnostic imaging and anthropometric and biochemical features were noted in a standardized form. The risk of steatosis and advanced fibrosis was assessed using commonly used algorithms (FLI, HSI, NAFLD-LFS, NAFLD ridge score, FIB-4 and NFS). RESULTS: In total 350 patients were included. Diagnostic imaging had been performed in 132 patients and of these, 34 (26%) had steatosis, which was not noted in the medical records in 16 (47%) patients. One patient with steatosis had been referred to a hepatologist. Of assessable patients, 71-97% had a high to intermediate risk of steatosis and 29-65% had an intermediate to high risk of advanced fibrosis according to the algorithms used. CONCLUSION: This study indicates a high prevalence of NAFLD among T2DM patients in Swedish primary care. Patients with known NAFLD were followed up to a very low extent. Using fibrosis algorithms in primary health care would result in many patients needing further assessment in secondary care.

Vasomotion analysis of speed resolved perfusion, oxygen saturation, red blood cell tissue fraction, and vessel diameter: Novel microvascular perspectives.

BACKGROUND: Vasomotion is the spontaneous oscillation in vascular tone in the microcirculation and is believed to be a physiological mechanism facilitating the transport of blood gases and nutrients to and from tissues. So far, Laser Doppler flowmetry has constituted the gold standard for in vivo vasomotion analysis. MATERIALS AND METHODS: We applied vasomotion analysis to speed-resolved perfusion, oxygen saturation, red blood cell tissue (RBC) tissue fraction, and average vessel diameter from five healthy individuals at rest measured by the newly developed Periflux 6000 EPOS system over 10 minutes. Magnitude scalogram and the time-averaged wavelet spectra were divided into frequency intervals reflecting endothelial, neurogenic, myogenic, respiratory, and cardiac function. RESULTS: Recurrent high-intensity periods of the myogenic, neurogenic, and endothelial frequency intervals were found. The neurogenic activity was considerably more pronounced for the oxygen saturation, RBC tissue fraction, and vessel diameter signals, than for the perfusion signals. In a correlation analysis we found that changes in perfusion in the myogenic, neurogenic, and endothelial frequency intervals precede changes in the other signals. Furthermore, changes in average vessel diameter were in general negatively correlated to the other signals in the same frequency intervals, indicating the importance of capillary recruitment. CONCLUSION: We conclude that vasomotion can be observed in signals reflecting speed resolved perfusion, oxygen saturation, RBC tissue fraction, and vessel diameter. The new parameters enable new aspects of the microcirculation to be observed.

Evaluating the prevalence and severity of NAFLD in primary care: the EPSONIP study protocol.

BACKGROUND: Non-alcoholic fatty liver disease (NAFLD) affects 20-30% of the general adult population. NAFLD patients with type 2 diabetes mellitus (T2DM) are at an increased risk of advanced fibrosis, which puts them at risk of cardiovascular complications, hepatocellular carcinoma, or liver failure. Liver biopsy is the gold standard for assessing hepatic fibrosis. However, its utility is inherently limited. Consequently, the prevalence and characteristics of T2DM patients with advanced fibrosis are unknown. Therefore, the purpose of the current study is to evaluate the prevalence and severity of NAFLD in patients with T2DM by recruiting participants from primary care, using the latest imaging modalities, to collect a cohort of well phenotyped patients. METHODS: We will prospectively recruit 400 patients with T2DM using biomarkers to assess their status. Specifically, we will evaluate liver fat content using magnetic resonance imaging (MRI); hepatic fibrosis using MR elastography and vibration-controlled transient elastography; muscle composition and body fat distribution using water-fat separated whole body MRI; and cardiac function, structure, and tissue characteristics, using cardiovascular MRI. DISCUSSION: We expect that the study will uncover potential mechanisms of advanced hepatic fibrosis in NAFLD and T2DM and equip the clinician with better diagnostic tools for the care of T2DM patients with NAFLD. TRIAL REGISTRATION: Clinicaltrials.gov, identifier NCT03864510. Registered 6 March 2019, https://clinicaltrials.gov/ct2/show/NCT03864510 .

Moisture sensor for exudative wounds - A pilot study.

BACKGROUND: Exudative wounds cause discomfort for patients. Introduction of a moisture sensor to dressings could facilitate change of dressings only when needed. The aim of this pilot study was to evaluate the ability of a newly developed moisture sensor to detect moisture in relation to the absorbing capacity of the dressing. MATERIALS AND METHODS: In five patients, with one leg ulcer each, three dressing changes per patient were observed. Interval of dressing change was according to clinical need and healthcare professional's decision. Sensor activation, dressing weight and complications were registered. To investigate the effect of dressing on sensor activation, half of the observations were made without an extra layer of non-woven between the dressing and sensor (Variant A), and half with (Variant B). RESULTS: The sensor indicated time for dressing change in six out of fifteen observations. Variants A and B did not differ regarding activation or the timing of the activation. CONCLUSIONS: The addition of a moisture sensor for facilitating management of exudative wounds is promising. We recommend future larger studies evaluating the potential clinical benefits and risks of the addition of a moisture sensor. We also recommend evaluation of potential home monitoring of wounds by a moisture sensor.

Microvascular effects of microneedle application.

BACKGROUND: The efficiency of transdermal drug delivery may be increased by pretreating the skin with microneedles, but distinct effects of microneedles and the microneedle-enhanced delivery of vasoactive drugs on the skin microvasculature are still not well investigated. MATERIALS AND METHODS: In eight healthy human subjects, we measured the microvascular response to microneedle-induced microtraumas in the skin microvasculature using polarized light spectroscopy imaging (Tissue Viability imaging, TiVi). The microvascular response was assessed for up to 48 hours for three microneedle sizes (300 µm, 500 µm, and 750 µm) and for different pressures and application times. RESULTS: In our results, microneedle application increased the local red blood cell (RBC) concentration for up to 24 hours dependent on the needle lengths, applied time, and force. CONCLUSION: Optimization of microneedles size, pressure, and application time should be taken into account for future protocols for drug delivery and experimental provocations.

Effect of NG -monomethyl l-arginine on microvascular blood flow and glucose metabolism after an oral glucose load.

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 NG -monomethyl l-arginine using microdialysis. METHODS: Microdialysis catheters, perfused with NG -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 NG -monomethyl l-arginine catheter compared to the control catheter (urea clearance: P < .006, glucose dialysate concentration: P < .035). No significant effect of NG -monomethyl l-arginine on microvascular blood flow was observed with laser speckle contrast imaging (P = .81). CONCLUSION: Local delivery of NG -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.

Vascular Occlusion in a Porcine Flap Model: Effects on Blood Cell Concentration and Oxygenation.

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.

Skin glucose metabolism and microvascular blood flow during local insulin delivery and after an oral glucose load.

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.

Monitoring of partial and full venous outflow obstruction in a porcine flap model using laser speckle contrast imaging.

BACKGROUND: In microsurgery, there is a demand for more reliable methods of post-operative monitoring of free flaps, especially with regard to tissue-threatening obstructions of the feeding arteries and draining veins. In this study, we evaluated laser speckle contrast imaging (LSCI) and laser Doppler flowmetry (LDF) to assess their possibilities to detect partial and full venous outflow obstruction, as well as full arterial occlusion, in a porcine flap model. METHODS: Cranial gluteal artery perforator flaps (CGAPs) were raised, and arterial and venous blood flow to and from the flaps was monitored using ultrasonic flow probes. The venous flow was altered with an inflatable cuff to simulate partial and full (50% and 100%) venous obstruction, and arterial flow was completely obstructed using clamps. The flap microcirculation was monitored using LSCI and LDF. RESULTS: Both LDF and the LSCI detected significant changes in flap perfusion. After partial (50%) venous occlusion, perfusion decreased from baseline, LSCI: 63.5 ± 12.9 PU (p = 0.01), LDF 31.3 ± 15.7 (p = 0.64). After 100% venous occlusion, a further decrease in perfusion was observed: LSCI 54.6 ± 14.2 PU (p < 0.001) and LDF 16.7 ± 12.8 PU (p < 0.001). After release of the venous cuff, LSCI detected a return of the perfusion to a level slightly, but not significantly, below the baseline level 70.1 ± 11.5 PU (p = 0.39), while the LDF signal returned to a level not significant from the baseline 36.1 ± 17.9 PU (p > 0.99). Perfusion during 100% arterial occlusion decreased significantly as measured with both methods, LSCI: 48.3 ± 7.7 (PU, p < 0.001) and LDF: 8.5 ± 4.0 PU (p < 0.001). During 50% and 100% venous occlusion, LSCI showed a 20% and 26% intersubject variability (CV%), respectively, compared to 50% and 77% for LDF. CONCLUSIONS: LSCI offers sensitive and reproducible measurements of flap microcirculation and seems more reliable in detecting decreases in blood perfusion caused by venous obstruction. It also allows for perfusion measurements in a relatively large area of flap tissue. This may be useful in identifying areas of the flap with compromised microcirculation during and after surgery.

Microvascular blood flow in scalds in children and its relation to duration of wound healing: A study using laser speckle contrast imaging.

BACKGROUND: Microvascular perfusion changes in scalds in children during the first weeks after injury is related to the outcome of healing, and measurements of perfusion, based on laser Doppler imaging, have been used successfully to predict the need for excision and grafting. However, the day-to-day changes in perfusion during the first weeks after injury have not to our knowledge been studied in detail. The aim of this study, based on a conservative treatment model where excision and grafting decisions were delayed to day 14 after injury, was to measure changes in perfusion in scalds using laser speckle contrast imaging (LSCI) during the first three weeks after injury. METHODS: We measured perfusion with LSCI in 34 patients at regular intervals between 6h after injury until complete reepithelialization or surgery. Duration of healing was defined as the time to complete reepithelialization. RESULTS: Less perfusion, between 6 and 96h after injury, was associated with longer duration of healing with the strongest association occurring between 72 and 96h. Burns that healed within 14 days had relatively high initial perfusion, followed by a peak and subsequent slow decrease. Both the maximum perfusion and the time-to-peak were dependent on the severity of the burn. Burns that needed excision and grafting had less initial perfusion and a gradual reduction over time. CONCLUSION: The perfusion in scalds in children shows characteristic patterns during the first weeks after injury depending on the duration of wound healing, the greatest difference between wounds of different severity being on the 4th day. Perfusion should therefore preferably be measured on the fourth day if it is to be used in the assessment of burn depth.

Non-Invasive Measurement of Skin Microvascular Response during Pharmacological and Physiological Provocations.

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; p<0.001) 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; p<0.001, LSCI: baseline 50.8±8.0 PU; max 151±22 PU; p<0.001) and RBC concentration (TiVi: baseline 49.2±32.9 AU; max 99.3±28.3 AU; p<0.001). After 5 minutes of forearm occlusion with prior exsanguination, a decrease was seen in perfusion (LDF: p = 0.027; LSCI: p<0.001) and in RBC concentration (p = 0.045). Only LSCI showed a significant decrease in perfusion after 5 minutes of occlusion without prior exsanguination (p<0.001). 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.

Assessment of microcirculation of the skin using Tissue Viability Imaging: A promising technique for detecting venous stasis in the skin.

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<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.