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Abstract Background Circulatory shock and multi-organ failure remain major contributors to morbidity and mortality in critically ill patients and are associated with insufficient oxygen availability in the tissue. Intrinsic mechanisms to improve tissue perfusion, such as up-regulation of functional capillary density (FCD) and red blood cell velocity (RBCv), have been identified as maneuvers to improve oxygen extraction by the tissues; however, their role in circulatory shock and potential use as resuscitation targets remains unknown. To fill this gap, we examined the baseline and maximum recruitable FCD and RBCv in response to a topical nitroglycerin stimulus (FCDNG, RBCvNG) in patients with and without circulatory shock to test whether this may be a method to identify the presence and magnitude of a microcirculatory reserve capacity important for identifying a resuscitation target. Methods Sublingual handheld vital microscopy was performed after initial resuscitation in mechanically ventilated patients consecutively admitted to a tertiary medical ICU. FCD and RBCv were quantified using an automated computer vision algorithm (MicroTools). Patients with circulatory shock were retrospectively identified via standardized hemodynamic and clinical criteria and compared to patients without circulatory shock. Results 54 patients (57 ± 14y, BMI 26.3 ± 4.9 kg/m2, SAPS 56 ± 19, 65% male) were included, 13 of whom presented with circulatory shock. Both groups had similar cardiac index, mean arterial pressure, RBCv, and RBCvNG. Heart rate (p

Background: Circulatory shock and multi-organ failure remain major contributors to morbidity and mortality in critically ill patients and are associated with insufficient oxygen availability in the tissue. Intrinsic mechanisms to improve tissue perfusion, such as up-regulation of functional capillary density (FCD) and red blood cell velocity (RBCv), have been identified as maneuvers to improve oxygen extraction by the tissues; however, their role in circulatory shock and potential use as resuscitation targets remains unknown. To fill this gap, we examined the baseline and maximum recruitable FCD and RBCv in response to a topical nitroglycerin stimulus (FCDNG, RBCvNG) in patients with and without circulatory shock to test whether this may be a method to identify the presence and magnitude of a microcirculatory reserve capacity important for identifying a resuscitation target. Methods: Sublingual handheld vital microscopy was performed after initial resuscitation in mechanically ventilated patients consecutively admitted to a tertiary medical ICU. FCD and RBCv were quantified using an automated computer vision algorithm (MicroTools). Patients with circulatory shock were retrospectively identified via standardized hemodynamic and clinical criteria and compared to patients without circulatory shock. Results: 54 patients (57 ± 14y, BMI 26.3 ± 4.9 kg/m2, SAPS 56 ± 19, 65% male) were included, 13 of whom presented with circulatory shock. Both groups had similar cardiac index, mean arterial pressure, RBCv, and RBCvNG. Heart rate (p < 0.001), central venous pressure (p = 0.02), lactate (p < 0.001), capillary refill time (p < 0.01), and Mottling score (p < 0.001) were higher in circulatory shock after initial resuscitation, while FCD and FCDNG were 10% lower (16.9 ± 4.2 and 18.9 ± 3.2, p < 0.01; 19.3 ± 3.1 and 21.3 ± 2.9, p = 0.03). Nitroglycerin response was similar in both groups, and circulatory shock patients reached FCDNG similar to baseline FCD found in patients without shock. Conclusion: Critically ill patients suffering from circulatory shock were found to present with a lower sublingual FCD. The preserved nitroglycerin response suggests a dysfunction of intrinsic regulation mechanisms to increase the microcirculatory oxygen extraction capacity associated with circulatory shock and identifies a potential resuscitation target. These differences in microcirculatory hemodynamic function between patients with and without circulatory shock were not reflected in blood pressure or cardiac index. [ABSTRACT FROM AUTHOR]

Temporal lobe epilepsy (TLE) is increasingly associated with blood-brain barrier dysfunction and microvascular alterations, yet the pathophysiological link is missing. An important barrier function is exerted by the glycocalyx, a gel-like layer coating the endothelium. To explore such associations, we used intraoperative videomicroscopy to quantify glycocalyx and microcirculation properties of the neocortex and hippocampus of 15 patients undergoing resective brain surgery as treatment for drug-resistant TLE, and 15 non-epileptic controls. Fluorescent lectin staining of neocortex and hippocampal tissue was used for blood vessel surface area quantification. Neocortical perfused boundary region, the thickness of the glycocalyx' impaired layer, was higher in patients (2.64 ± 0.52 µm) compared to controls (1.31 ± 0.29 µm), P < 0.01, indicative of reduced glycocalyx integrity in patients. Moreover, erythrocyte flow velocity analysis revealed an impaired ability of TLE patients to (de-)recruit capillaries in response to changing metabolic demands (R 2 = 0.75, P < 0.01), indicating failure of neurovascular coupling mechanisms. Blood vessel quantification comparison between intraoperative measurements and resected tissue showed strong correlation (R 2 = 0.94, P < 0.01). This is the first report on in vivo assessment of glycocalyx and microcirculation properties in TLE patients, confirming the pivotal role of cerebrovascular changes. Further assessment of the cerebral microcirculation in relation to epileptogenesis might open avenues for new therapeutic targets for drug-resistant epilepsy. [ABSTRACT FROM AUTHOR]

Aim: Skeletal muscle convective and diffusive oxygen (O2) transport are peripheral determinants of exercise capacity in both patients with chronic obstructive pulmonary disease (COPD) and chronic heart failure (CHF). We hypothesised that differences in these peripheral determinants of performance between COPD and CHF patients are revealed during small muscle mass exercise, where the cardiorespiratory limitations to exercise are diminished. Methods: Eight patients with moderate to severe COPD, eight patients with CHF (NYHA II), and eight age- and sex-matched controls were studied. We measured leg blood flow (Q'leg) by Doppler ultrasound during submaximal one legged knee-extensor exercise (KEE), while sampling arterio-venous variables across the leg. The capillary oxyhaemoglobin dissociation curve was reconstructed from paired femoral arterial-venous oxygen tensions and saturations, which enabled the estimation of O2 parameters at the microvascular level within skeletal muscle, so that skeletal muscle oxygen conductance (DSMO2) could be calculated and adjusted for flow (DSMO2/ Q'leg) to distinguish convective from diffusive oxygen transport. Results: During KEE, Q'leg increased to a similar extent in CHF (2.0 (0.4) L/min) and controls (2.3 (0.3) L/min), but less in COPD patients (1.8 (0.3) L/min) (p <0.03). There was no difference in resting DSMO2 between COPD and CHF and when adjusting for flow, the DSMO2 was higher in both groups compared to controls (COPD: 0.97 (0.23) vs. controls 0.63 (0.24) mM/kPa, p= 0.02; CHF 0.98 (0.11) mM/kPa vs. controls, p= 0.001). The Q_ -adjusted DSMO2 was not different in COPD and CHF during KEE (COPD: 1.19 (0.11) vs. CHF: 1.00 (0.18) mM/kPa; p= 0.24) but higher in COPD vs. controls: 0.87 (0.28) mM/kPa (p= 0.02), and only CHF did not increase Q_ -adjusted DSMO2 from rest (p= 0.2). Conclusion: Disease-specific factors may play a role in peripheral exercise limitation in patients with COPD compared with CHF. Thus, low convective O2 transport to contracting muscle seemed to predominate in COPD, whereas muscle diffusive O2 transport was unresponsive in CHF. [ABSTRACT FROM AUTHOR]

Aim: Skeletal muscle convective and diffusive oxygen (O2) transport are peripheral determinants of exercise capacity in both patients with chronic obstructive pulmonary disease (COPD) and chronic heart failure (CHF). We hypothesised that differences in these peripheral determinants of performance between COPD and CHF patients are revealed during small muscle mass exercise, where the cardiorespiratory limitations to exercise are diminished.Methods: Eight patients with moderate to severe COPD, eight patients with CHF (NYHA II), and eight age- and sex-matched controls were studied. We measured leg blood flow (Q̇leg) by Doppler ultrasound during submaximal one-legged knee-extensor exercise (KEE), while sampling arterio-venous variables across the leg. The capillary oxyhaemoglobin dissociation curve was reconstructed from paired femoral arterial-venous oxygen tensions and saturations, which enabled the estimation of O2 parameters at the microvascular level within skeletal muscle, so that skeletal muscle oxygen conductance (DSMO2) could be calculated and adjusted for flow (DSMO2/Q̇leg) to distinguish convective from diffusive oxygen transport.Results: During KEE, Q̇leg increased to a similar extent in CHF (2.0 (0.4) L/min) and controls (2.3 (0.3) L/min), but less in COPD patients (1.8 (0.3) L/min) (p

Abstract Background The availability of handheld, noninvasive sublingual video-microscopes allows for visualization of the microcirculation in critically ill patients. Recent studies demonstrate that reduced numbers of blood-perfused microvessels and increased penetration of erythrocytes into the endothelial glycocalyx are essential components of microvascular dysfunction. The aim of this study was to identify novel microvascular variables to determine the level of microvascular dysfunction in sepsis and its relationship with clinical variables. Methods This observational, prospective, cross-sectional study included 51 participants, of which 34 critically ill sepsis patients were recruited from intensive care units of a university hospital. Seventeen healthy volunteers served as controls. All participants underwent sublingual videomicroscopy by sidestream darkfield imaging. A new developed version of the Glycocheck™ software was used to quantify vascular density, perfused boundary region (PBR-an inverse variable of endothelial glycocalyx dimensions), red blood cell (RBC) velocity, RBC content, and blood flow in sublingual microvessels with diameters between 4 and 25 µm. Results A detailed analysis of adjacent diameter classes (1 µm each) of vessels between 4 and 25 µm revealed a severe reduction of vascular density in very small capillaries (5–7 µm), which correlated with markers of sepsis severity. Analysis of RBC velocity (VRBC) revealed a strong dependency between capillary and feed vessel VRBC in sepsis patients (R 2 = 0.63, p

Objective: Diabetic kidney disease is a microvascular complication of diabetes. Here, we assessed the association between skin microvascular function and renal hemodynamic function in a cohort of well‐phenotyped adults with type 2 diabetes (T2D). Methods: We included 81 overweight/obese adults (age: 62 ± 8 years; BMI: 32 ± 4 kg/m2) with well‐controlled T2D and no renal impairment. Skin microvascular function was assessed by nailfold capillary density in rest and after arterial occlusion (ie, peak capillary density). Renal hemodynamic functions (ie, measured glomerular filtration rate [mGFR], effective renal blood flow [ERBF], filtration fraction [FF], and effective renal vascular resistance [ERVR]) were assessed by combined inulin and para‐aminohippurate clearances and blood pressure measurements. Results: Skin capillary density was 45 ± 10 capillaries/mm2 at baseline and 57 ± 11 capillaries/mm2 during post‐occlusive peak; mGFR averaged 108 ± 20 ml/min. In multivariable regression analyses, positive associations between capillary density during post‐occlusive peak and mGFR (β = 0.224; p = 0.022) and ERBF (β = 0.203; p = 0.020) and a positive trend for hyperemia and mGFR (β = 0.391; p = 0.053) were observed, while a negative association for post‐occlusive capillary density with ERVR (β = −0.196; p = 0.027) was found. Conclusion: These findings indicate that microvascular dysfunction in overweight adults with T2D is associated with lower mGFR and ERPF and higher ERVR. We hypothesize that increased renal vascular resistance may contribute to glomerular dysfunction due to impaired renal perfusion. [ABSTRACT FROM AUTHOR]

To shed light on how acute exercise affects blood glucose (BG) concentrations in nondiabetic subjects, we develop a physiological pharmacokinetic/pharmacodynamic model of postprandial glucose dynamics during exercise. We unify several concepts of exercise physiology to derive a multiscale model that includes three important effects of exercise on glucose dynamics: increased endogenous glucose production (EGP), increased glucose uptake in skeletal muscle (SM), and increased glucose delivery to SM by capillary recruitment (i.e. an increase in surface area and blood flow in capillary beds). We compare simulations to experimental observations taken in two cohorts of healthy nondiabetic subjects (resting subjects (n = 12) and exercising subjects (n = 12)) who were each given a mixed-meal tolerance test. Metabolic tracers were used to quantify the glucose flux. Simulations reasonably agree with postprandial measurements of BG concentration and EGP during exercise. Exercise-induced capillary recruitment is predicted to increase glucose transport to SM by 100%, causing hypoglycemia. When recruitment is blunted, as in those with capillary dysfunction, the opposite occurs and higher than expected BG levels are predicted. Model simulations show how three important exercise-induced phenomena interact, impacting BG concentrations. This model describes nondiabetic subjects, but it is a first step to a model that describes glucose dynamics during exercise in those with type 1 diabetes (T1D). Clinicians and engineers can use the insights gained from the model simulations to better understand the connection between exercise and glucose dynamics and ultimately help patients with T1D make more informed insulin dosing decisions around exercise. [ABSTRACT FROM AUTHOR]

Background: The availability of handheld, noninvasive sublingual video-microscopes allows for visualization of the microcirculation in critically ill patients. Recent studies demonstrate that reduced numbers of blood-perfused microvessels and increased penetration of erythrocytes into the endothelial glycocalyx are essential components of microvascular dysfunction. The aim of this study was to identify novel microvascular variables to determine the level of microvascular dysfunction in sepsis and its relationship with clinical variables.Methods: This observational, prospective, cross-sectional study included 51 participants, of which 34 critically ill sepsis patients were recruited from intensive care units of a university hospital. Seventeen healthy volunteers served as controls. All participants underwent sublingual videomicroscopy by sidestream darkfield imaging. A new developed version of the Glycocheck™ software was used to quantify vascular density, perfused boundary region (PBR-an inverse variable of endothelial glycocalyx dimensions), red blood cell (RBC) velocity, RBC content, and blood flow in sublingual microvessels with diameters between 4 and 25 µm.Results: A detailed analysis of adjacent diameter classes (1 µm each) of vessels between 4 and 25 µm revealed a severe reduction of vascular density in very small capillaries (5-7 µm), which correlated with markers of sepsis severity. Analysis of RBC velocity (VRBC) revealed a strong dependency between capillary and feed vessel VRBC in sepsis patients (R2 = 0.63, p < 0.0001) but not in healthy controls (R2 = 0.04, p = 0.43), indicating impaired capillary (de-)recruitment in sepsis. This finding enabled the calculation of capillary recruitment and dynamic capillary blood volume (CBVdynamic). Moreover, adjustment of PBR to feed vessel VRBC further improved discrimination between sepsis patients and controls by about 50%. By combining these dynamic microvascular and glycocalyx variables, we developed the microvascular health score (MVHSdynamic™), which decreased from 7.4 [4.6-8.7] in controls to 1.8 [1.4-2.7] in sepsis patients (p < 0.0001) and correlated with sepsis severity.Conclusion: We introduce new important diameter-specific quantification and differentiated analysis of RBC kinetics, a key to understand microvascular dysfunction in sepsis. MVHSdynamic, which has a broad bandwidth to detect microvascular (dys-) function, might serve as a valuable tool to detect microvascular impairment in critically ill patients. [ABSTRACT FROM AUTHOR]

The regulation of oxygen and blood supply during isometric muscle actions is still unclear. Recently, two behavioral types of oxygen saturation (SvO2) and relative hemoglobin amount (rHb) in venous microvessels were described during a fatiguing holding isometric muscle action (HIMA) (type I: nearly parallel behavior of SvO2 and rHb; type II: partly inverse behavior). The study aimed to ascertain an explanation of these two regulative behaviors. Twelve subjects performed one fatiguing HIMA trial with each arm by weight holding at 60% of the maximal voluntary isometric contraction (MVIC) in a 90° elbow flexion. Six subjects additionally executed one fatiguing PIMA trial by pulling on an immovable resistance with 60% of the MVIC with each side and same position. Both regulative types mentioned were found during HIMA (I: n = 7, II: n = 17) and PIMA (I: n = 3, II: n = 9). During the fatiguing measurements, rHb decreased initially and started to increase in type II at an average SvO2-level of 58.75 ± 2.14%. In type I, SvO2 never reached that specific value during loading. This might indicate the existence of a threshold around 59% which seems to trigger the increase in rHb and could explain the two behavioral types. An approach is discussed to meet the apparent incompatibility of an increased capillary blood filling (rHb) despite high intramuscular pressures which were found by other research groups during isometric muscle actions.

These studies test, using intravital microscopy (IVM), the hypotheses that perfusion effects on insulin-stimulated muscle glucose uptake (MGU) are 1) capillary recruitment independent and 2) mediated through the dispersion of glucose rather than insulin. For experiment 1, capillary perfusion was visualized before and after intravenous insulin. No capillary recruitment was observed. For experiment 2, mice were treated with vasoactive compounds (sodium nitroprusside, hyaluronidase, and lipopolysaccharide), and dispersion of fluorophores approximating insulin size (10- kDa dextran) and glucose (2-NBDG) was measured using IVM. Subsequently, insulin and 2[14C]deoxyglucose were injected and muscle phospho-2[14C]deoxyglucose (2[C14]DG) accumulation was used as an index of MGU. Flow velocity and 2-NBDG dispersion, but not perfused surface area or 10-kDa dextran dispersion, predicted phospho-2[14C]DG accumulation. For experiment 3, microspheres of the same size and number as are used for contrast-enhanced ultrasound (CEU) studies of capillary recruitment were visualized using IVM. Due to their low concentration, microspheres were present in only a small fraction of blood-perfused capillaries. Microsphereperfused blood volume correlated to flow velocity. These findings suggest that 1) flow velocity rather than capillary recruitment controls microvascular contributions to MGU, 2) glucose dispersion is more predictive of MGU than dispersion of insulin-sized molecules, and 3) CEU measures regional flow velocity rather than capillary recruitment. [ABSTRACT FROM AUTHOR]

The incidence of cardiovascular diseases in vegetarian individuals is lower than that in the general population. Nevertheless, individuals who adhere to vegan diets have a higher prevalence of hyperhomocysteinemia with eventual adverse effects on vascular reactivity. Creatine supplementation (CrS) reduces plasma homocysteine levels and enhances vascular reactivity in the microcirculation. Thus, we investigated the effects of CrS on systemic microcirculation and homocysteine blood levels in strict vegan subjects. Forty‐nine strict vegan subjects were allocated to the oral CrS (5 g micronized creatine monohydrate daily for three weeks; n = 31) and placebo (n = 18) groups. Laser speckle contrast imaging coupled with acetylcholine skin iontophoresis was used to evaluate cutaneous microvascular reactivity, and intravital video‐microscopy was used to evaluate skin capillary density and reactivity before and after CrS. We demonstrated that CrS reduces the plasma levels of homocysteine and increases those of folic acid. After the CrS period, the homocysteine levels of all of the vegan subjects normalized. CrS also induced increases in baseline skin functional capillary density and endothelium‐dependent capillary recruitment in both normo‐ (N‐Hcy) and hyperhomocysteinemic (H‐Hcy) individuals. CrS increased endothelium‐dependent skin microvascular vasodilation in the H‐Hcy vegan subjects but not in the N‐Hcy vegan subjects. In conclusion, three weeks of oral CrS was sufficient to increase skin capillary density and recruitment and endothelium‐dependent microvascular reactivity. CrS also resulted in plasma increases in folic acid levels and reductions in homocysteine levels among only the H‐Hcy individuals. [ABSTRACT FROM AUTHOR]

Key points: It has been postulated that increased blood flow‐associated shear stress on endothelial cells is an underlying mechanism by which physical activity enhances insulin‐stimulated vasodilatation.This report provides evidence supporting the hypothesis that increased shear stress exerts insulin‐sensitizing effects in the vasculature and this evidence is based on experiments in vitro in endothelial cells, ex vivo in isolated arterioles and in vivo in humans.Given the recognition that vascular insulin signalling, and associated enhanced microvascular perfusion, contributes to glycaemic control and maintenance of vascular health, strategies that stimulate an increase in limb blood flow and shear stress have the potential to have profound metabolic and vascular benefits mediated by improvements in endothelial insulin sensitivity. The vasodilator actions of insulin contribute to glucose uptake by skeletal muscle, and previous studies have demonstrated that acute and chronic physical activity improves insulin‐stimulated vasodilatation and glucose uptake. Because this effect of exercise primarily manifests in vascular beds highly perfused during exercise, it has been postulated that increased blood flow‐associated shear stress on endothelial cells is an underlying mechanism by which physical activity enhances insulin‐stimulated vasodilatation. Accordingly, herein we tested the hypothesis that increased shear stress, in the absence of muscle contraction, can acutely render the vascular endothelium more insulin‐responsive. To test this hypothesis, complementary experiments were conducted using (1) cultured endothelial cells, (2) isolated and pressurized skeletal muscle arterioles from swine, and (3) humans. In cultured endothelial cells, 1 h of increased shear stress from 3 to 20 dynes cm−2 caused a significant shift in insulin signalling characterized by greater activation of eNOS relative to MAPK. Similarly, isolated arterioles exposed to 1 h of intraluminal shear stress (20 dynes cm−2) subsequently exhibited greater insulin‐induced vasodilatation compared to arterioles kept under no‐flow conditions. Finally, we found in humans that increased leg blood flow induced by unilateral limb heating for 1 h subsequently augmented insulin‐stimulated popliteal artery blood flow and muscle perfusion. In aggregate, these findings across models (cells, isolated arterioles and humans) support the hypothesis that elevated shear stress causes the vascular endothelium to become more insulin‐responsive and thus are consistent with the notion that shear stress may be a principal mechanism by which physical activity enhances insulin‐stimulated vasodilatation. Key points: It has been postulated that increased blood flow‐associated shear stress on endothelial cells is an underlying mechanism by which physical activity enhances insulin‐stimulated vasodilatation.This report provides evidence supporting the hypothesis that increased shear stress exerts insulin‐sensitizing effects in the vasculature and this evidence is based on experiments in vitro in endothelial cells, ex vivo in isolated arterioles and in vivo in humans.Given the recognition that vascular insulin signalling, and associated enhanced microvascular perfusion, contributes to glycaemic control and maintenance of vascular health, strategies that stimulate an increase in limb blood flow and shear stress have the potential to have profound metabolic and vascular benefits mediated by improvements in endothelial insulin sensitivity. [ABSTRACT FROM AUTHOR]

Our objective is to develop a physiology-based model of insulin kinetics to understand how exercise alters insulin concentrations in those with type 1 diabetes (T1D). We reveal the relationship between the insulin absorption rate (kaI) from subcutaneous tissue, the insulin delivery rate (kdI) to skeletal muscle, and two physiological parameters that characterize the tissue: the perfusion rate (Q) and the capillary permeability surface area (PS), both of which increase during exercise because of capillary recruitment. We compare model predictions to experimental observations from two pump-wearing T1D cohorts [resting subjects (n=17) and exercising subjects (n=12)] who were each given a mixed-meal tolerance test and a bolus of insulin. Using independently measured values of Q and PS from literature, the model predicts that during exercise insulin concentration increases by 30% in plasma and by 60% in skeletal muscle. Predictions reasonably agree with experimental observations from the two cohorts, without the need for parameter estimation by curve fitting. The insulin kinetics model suggests that the increase in surface area associated with exercise-induced capillary recruitment significantly increases kaI and kdI, which explains why insulin concentrations in plasma and skeletal muscle increase during exercise, ultimately enhancing insulin-dependent glucose uptake. Preventing hypoglycemia is of paramount importance in determining the proper insulin dose during exercise. The presented model provides mechanistic insight into how exercise affects insulin kinetics, which could be useful in guiding the design of decision support systems and artificial pancreas control algorithms. [ABSTRACT FROM AUTHOR]

Aims: In type 2 diabetes impaired insulin‐induced muscle perfusion is thought to contribute to reduced whole‐body glucose uptake. In this study, we examined the effects of iloprost, a stable prostacyclin analogue, on insulin‐induced muscle capillary recruitment and whole‐body glucose uptake. Materials and Methods: In a randomized cross‐over design, 12 type 2 diabetes patients (age, 55 [46‐69] years; BMI, 33.1 [31.0‐39] kg/m2) underwent two hyperinsulinaemic‐euglycaemic clamps, one with and one without simultaneous low‐dose iloprost infusion. Contrast‐enhanced ultrasonography of the vastus lateralis muscle was performed before and during the clamp. Muscle capillary recruitment was calculated as percentage change in microvascular blood volume (MBV) before and during the clamp. Results: Insulin infusion reduced skeletal muscle MBV by ~50% compared to the fasting state (fasting, 1.77·10−4 [1.54·10−5–2.44·10−3] arbitrary units (AU); hyperinsulinaemia, 6.69·10−5 [2.68·10−6–5.72·10−4] AU; P = 0.050). Infusion of iloprost prevented this insulin‐induced skeletal muscle capillary derecruitment, from (−49.5 [−89.5 to 55.3] %) to (8.0 [−68.8 to 306.6] %), for conditions without and with iloprost, respectively. The rate of glucose disappearance (Rd) did not change significantly during iloprost infusion (17.3 [10.0‐40.8] μmol/kg/min) compared with insulin infusion alone (17.6 [9.9‐68.7] μmol/kg/min). Conclusions: Our data suggest that acute improvement in insulin‐stimulated muscle perfusion is not an attractive therapeutic approach to bypass cellular resistance to glucose uptake in type 2 diabetes. Whether long‐term improvements in insulin‐induced muscle perfusion may prove beneficial for glucose disposal remains to be determined. [ABSTRACT FROM AUTHOR]

Summary: Methods capable of measuring blood flow in a tissue‐specific manner are needed. The purpose of this study was to investigate whether contrast‐enhanced ultrasound (CEUS) using bolus injections of SonoVue® is an useful method for assessing postprandial changes in microvascular perfusion in the vastus lateralis muscle. Ten healthy, young subjects were recruited for this study. Six subjects participated in washout and reproducibility protocols to assess washout time of SonoVue® and the reproducibility of the method when measuring microvascular blood volume (MBV). Six subjects (two of which also participated in the washout and reproducibility protocols) participated in exercise and nutrition protocols, to assess the ability of the method to detect changes in MBV in response to these interventions. Intraday variation (coefficients of variation) for MBV indices, as assessed by peak signal intensity (PI) or mean plateau signal intensity (mPI), was high (PI: 19 ± 4·2%; mPI: 23 ± 3·3%). The exercise protocol induced significant increases in MBV indices (PI:+113%, P˂0·0001; mPI:+218%, P˂0·0001) acutely after exercise cessation. There were no changes in MBV indices in response to feeding during the nutrition protocol (PI: P = 0·51; mPI: P = 0·51). We conclude that CEUS using bolus injections of SonoVue® is not capable of detecting changes in MBV of vastus lateralis in response to feeding. This is probably due to the low reproducibility of the method. However, the method is capable of measuring changes in MBV in response to exercise. This method could therefore be used when investigating exercise‐induced changes in microvascular perfusion. [ABSTRACT FROM AUTHOR]

Abstract: Objective: Changes in microvascular perfusion have been reported in many diseases, yet the functional significance of altered perfusion is often difficult to determine. This is partly because commonly used techniques for perfusion measurement often rely on either indirect or by‐hand approaches. Methods: We developed and validated a fully automated software technique to measure microvascular perfusion in videos acquired by fluorescence microscopy in the mouse gastrocnemius. Acute perfusion responses were recorded following intravenous injections with phenylephrine, SNP, or saline. Results: Software‐measured capillary flow velocity closely correlated with by‐hand measured flow velocity (R2 = 0.91, P < 0.0001). Software estimates of capillary hematocrit also generally agreed with by‐hand measurements (R2 = 0.64, P < 0.0001). Detection limits range from 0 to 2000 μm/s, as compared to an average flow velocity of 326 ± 102 μm/s (mean ± SD) at rest. SNP injection transiently increased capillary flow velocity and hematocrit and made capillary perfusion more steady and homogenous. Phenylephrine injection had the opposite effect in all metrics. Saline injection transiently decreased capillary flow velocity and hematocrit without influencing flow distribution or stability. All perfusion metrics were temporally stable without intervention. Conclusions: These results demonstrate a novel and sensitive technique for reproducible, user‐independent quantification of microvascular perfusion. [ABSTRACT FROM AUTHOR]

Objectives It has been hypothesized that obesity is the primary cause of microvascular dysfunction (MD), which could be a pathway to increase blood pressure and decrease insulin sensitivity. Due to the high prevalence of this metabolic disorder in the world today, the aim of this study was to investigate which is the most appropriate videocapillaroscopic method, between nailfold and dorsal finger, to assess microvascular function in obese patients since both techniques are non-invasive and could be used for early detection as well as for follow-up. Methods Eighteen lean [27.8 ± 6.2 years, body mass index (BMI) 21.8 ± 1.8 kg/m 2 ] and nineteen obese (30.8 ± 4.6 years; BMI 32.3 ± 1.5 kg/m 2 ) women participated in the study. Dynamic nailfold videocapillaroscopy assessed morphological (capillary diameters) and functional [functional capillary density (FCD); red blood cell velocity (RBCV) at baseline and peak and time (TRBCV max ) taken to reach it during the post-occlusive reactive hyperemia (PORH) response, after 1-min ischemia] parameters; while dorsal finger videocapillaroscopy assessed FCD at rest and capillary recruitment during PORH and post-venous occlusion. Results RBCV (0.32 ± 0.01 vs. 0.30 ± 0.01 mm/s; p < 0.0001) and RBCV max (0.32 ± 0.01 vs. 0.30 ± 0.015 mm/s; p = 0.0020) were significantly higher in control subjects compared to the obese group. Moreover, TRBCV max was prolonged in the obese group compared to control one (3.5 ± 1.4 vs. 5.5 ± 1.3 s; p = 0.0001). Multiple regression analysis showed that these variables were influenced by some others, especially those related to adiposity and metabolic disease. On the other hand, dorsal finger videocapillaroscopy did not show any significant differences between groups. Conclusion Our results strongly suggest that microvascular dysfunction consequent to obesity could be better detected by dynamic nailfold videocapillaroscopy than by dorsal finger videocapillaroscopy. [ABSTRACT FROM AUTHOR]

Objective: To compare capillary diameters, density and reactivity in high-risk pregnancies complicated by pregnancy-induced hypertension (PIH) to other high-risk pregnancies not affecting microcirculation (O).Methods: Patients hospitalized at a tertiary referral center from January to May 2012 were enrolled in the prospective pilot study. Five microscopic fields were recorded from the nailfold for capillary diameters and functional capillary density assessment. One microscopic field was assessed before and after venous congestion to evaluate the change in capillary diameters. The results were expressed as median (interquartile range). Wilcoxon rank-sum test was used for the analysis of statistical significance (level of significance was set top < 0.05).Results: In total, 31 patients were available for statistical analysis (PIH = 17;O = 14). Patients in the PIH group had significantly longer capillaries (123(91;182) vs. 72(65;107)μm,p = 0.003) and higher average capillary diameter (12(10;13) vs. 10(9;11)μm,p = 0.017). The difference in mean functional capillary density was not significant (20(17;25) vs. 19(15:21),p > 0.05), however, significantly reduced capillary recruitment (1(0;7) vs. 10(6;17),p = 0.006) was found in PIH. Preeclampsia was observed in 10 patients from the PIH group. These patients did not significantly differ from the rest of the PIH group in the abovementioned variables.Conclusion: This is the first pilot study concerning change of capillary diameters after venous congestion in pregnancy. The reduced capillary recruitment and reduced capability of further dilation of capillaries after venous congestion observed in women with PIH may suggest a significantly reduced functional capacity of the microcirculation and increased load on capillary endothelium in pregnancy complicated by gestational hypertension. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) has been shown to be involved in skeletal muscle glucose uptake during contraction/ exercise, especially in individuals with Type 2 diabetes (T2D). To examine the potential mechanisms, we examined the effect of local NO synthase (NOS) inhibition on muscle glucose uptake and muscle capillary blood flow during contraction in healthy and T2D rats. T2D was induced in Sprague-Dawley rats using a combined high-fat diet (23% fat wt/wt for 4 wk) and low-dose streptozotocin injections (35 mg/kg). Anesthetized animals had one hindlimb stimulated to contract in situ for 30 min (2 Hz, 0.1 ms, 35 V) with the contralateral hindlimb rested. After 10 min, the NOS inhibitor, W-nitro-L-arginine methyl ester (L-NAME; 5 μM) or saline was continuously infused into the femoral artery of the contracting hindlimb until the end of contraction. Surprisingly, there was no increase in skeletal muscle NOS activity during contraction in either group. Local NOS inhibition had no effect on systemic blood pressure or muscle contraction force, but it did cause a significant attenuation of the increase in femoral artery blood flow in control and T2D rats. However, NOS inhibition did not attenuate the increase in muscle capillary recruitment during contraction in these rats. Muscle glucose uptake during contraction was significantly higher in T2D rats compared with controls but, unlike our previous findings in hooded Wistar rats, NOS inhibition had no effect on glucose uptake during contraction. In conclusion, NOS inhibition did not affect muscle glucose uptake during contraction in control or T2D Sprague-Dawley rats, and this may have been because there was no increase in NOS activity during contraction. [ABSTRACT FROM AUTHOR]

Background Dietary creatine supplementation (CrS) is a practice commonly adopted by physically active individuals. However, the effects of CrS on systemic microvascular reactivity and density have never been reported. Additionally, CrS is able to influence blood levels of homocysteine, resulting in presumed effects on vascular endothelial function. Thus, we investigated the effects of CrS on the systemic microcirculation and on homocysteine levels in healthy young individuals. Methods This open-label study was performed on a group of 40 healthy male, moderately physically active subjects aged 27.7 ± 13.4 years who received one week of CrS at a dose of 20 g/day of commercially available micronized creatine monohydrate. Laser speckle contrast imaging was used in the evaluation of cutaneous microvascular reactivity, and intra-vital video microscopy was used to evaluate skin capillary density and reactivity, before and after CrS. CrS did not alter plasma levels of homocysteine, although CrS increased creatinine (p = 0.0001) and decreased uric acid (p = 0.0004) plasma levels. Significant changes in total cholesterol (p = 0.0486) and LDL-cholesterol (p = 0.0027) were also observed along with a reduction in plasma levels of T3 (p = 0.0074) and an increase in T4 levels (p = 0.0003). Skin functional capillary density (p = 0.0496) and capillary recruitment during post-occlusive reactive hyperemia (p = 0.0043) increased after CrS. Increases in cutaneous microvascular vasodilation induced by post-occlusive reactive hyperemia (p = 0.0078) were also observed. Conclusions Oral supplementation with creatine in healthy, moderately physically active young adults improves systemic endothelial-dependent microvascular reactivity and increases skin capillary density and recruitment. These effects are not concurrent with changes in plasma homocysteine levels. [ABSTRACT FROM AUTHOR]

Objective Insulin-induced capillary recruitment is considered a significant regulator of overall insulin-stimulated glucose uptake. Insulin's action to recruit capillaries has been hypothesized to involve insulin-induced changes in vasomotion. Data directly linking vasomotion to capillary perfusion, however, are presently lacking. We, therefore, investigated whether insulin's actions on capillary recruitment and vasomotion were interrelated in a group of healthy individuals. We further assessed the role of capillary recruitment in the association between vasomotion and insulin-mediated glucose uptake. Methods Changes in vasomotion and capillary density were determined by LDF and capillary videomicroscopy in skin, respectively, before and during a hyperinsulinemic euglycemic clamp in 19 healthy volunteers. Results Insulin-induced increase in the neurogenic vasomotion domain was positively related to insulin-augmented capillary recruitment ( r = 0.51, p = 0.04), and both parameters were related to insulin-mediated glucose uptake ( r = 0.47, p = 0.06 and r = 0.73, p = 0.001, respectively). The change in insulin-augmented capillary recruitment could, at least statistically, largely explain the association between the neurogenic domain and insulin-mediated glucose uptake. Conclusions Insulin-induced changes in vasomotion and capillary recruitment are associated in healthy volunteers. These data suggest that insulin's action to recruit capillaries may in part involve action on the neurogenic vasomotion domain, thereby enhancing capillary perfusion and glucose uptake. [ABSTRACT FROM AUTHOR]

The present study was undertaken to determine the effect of arterial blood hypoxemia induced by acute systemic hypoxia (pO2 =12%) on capillary recruitment and diameter, and red blood cell (RBC) velocity in human nail fold capillaries during rest, arterial post-occlusive reactive hyperemia (PRH), and venous occlusion (VO) using intravital video-capillaroscopy. Capillary recruitment was unchanged in acute systemic hypoxia (H) versus normoxia (N). There was no difference in RBC velocity measurements between normoxia and hypoxia (P<0.63). However, a statistically significant increase in nail fold capillary total width (N, 39.9±9.1 vs. H, 42.7±10.3μm; P<0.05), apical diameter (N, 15.5±4.3 vs. H, 16.8±4.3μm; P<0.05), arterial diameter (N, 11.9±3.5 vs. H, 13.9±4.1μm; P<0.05), and venous diameter (N, 15.5±4.3 vs. H, 17.2±4.8μm; P<0.05) was observed and continued to be significant most often during post-occlusive reactive hyperemia (PRH) and venous congestion (VO). These data suggest that acute systemic hypoxia does not increase capillary recruitment, but instead increases capillary diameter, resulting in increased capillary blood flow. [ABSTRACT FROM AUTHOR]

The insulinotropic gut hormone, glucagon-like-peptide-1 (GLP-1) has been proposed to have effects on vascular function and glucose disposal. However, whether GLP-1 is able to increase microvascular recruitment (MVR) in humans has not been investigated. GLP-1 was infused in the femoral artery in overnight fasted healthy young men. Microvascular recruitment was measured with real time contrast-enhanced ultrasound and leg glucose uptake by the leg balance technique with and without inhibition of the insulinotropic response of GLP-1 by co-infusion of octreotide. As a positive control, MVR and leg glucose uptake were measured during a hyperinsulinemic euglycemic clamp. Infusion of GLP-1 caused a rapid increase (P < 0.05) of 20% ± 12% (mean ± SE) in MVR in the vastus lateralis muscle of the infused leg after 5 min and MVR further increased to 60%±8% above pre-infusion levels by 60 min infusion. The effect was slightly slower but similar in magnitude in the non-infused contralateral leg in which GLP-1 concentration was within the physiological range. Octreotide-infusion did not prevent the GLP-1 induced increase in MVR. GLP-1 infusion did not increase leg glucose uptake with or without octreotide co-infusion. GLP-1 infusion in rats increased MVR by 28% (P < 0.05) but did not increase muscle glucose uptake. During the hyperinsulinemic clamp, MVR increased ~40% and leg glucose uptake increased 24 fold. It is concluded that GLP-1 in physiological concentrations causes a rapid insulin-independent increase in muscle MVR, but does not affect muscle glucose uptake. Thus, increasing microvascular recruitment without concomitant direct effects on muscle does not increase glucose uptake. [ABSTRACT FROM AUTHOR]

The skeletal muscle is one of the major target organs of insulin and plays an essential role in insulin-induced glucose uptake. Some evidence indicates that insulin delivery to skeletal muscle interstitium through the endothelial cells is the rate-limiting step in insulin-stimulated glucose uptake. Researchers have also found that this process is impaired by insulin resistance in type 2 diabetes and obesity. A recent study of ours demonstrated that insulin signaling in the endothelial cells plays a pivotal role in the regulation of glucose uptake by the skeletal muscle. Specifically, impaired insulin signaling in the endothelial cells, with reduction of insulin-induced eNOS phosphorylation, causes attenuation of the insulin-induced capillary recruitment and insulin delivery, which, in turn reduces glucose uptake by the skeletal muscle in high-fat diet-fed mice. Moreover, restoration of the insulin-induced eNOS phosphorylation in the endothelial cells completely reverses the reduction in the capillary recruitment and insulin delivery, and as a result, significantly restores glucose uptake by the skeletal muscle. In the present review, we describe the recent progress in research on the physiological and pathophysiological roles of endothelial insulin signaling in the regulation of insulin-induced glucose uptake by the skeletal muscle. [ABSTRACT FROM AUTHOR]

Purpose: To identify associations between long-term (1 year) food intake and skin nutritive microvascular function in healthy subjects. Methods: This was a cross-sectional study. A validated 88-item food-frequency questionnaire was administered to 39 healthy men aged 23.4 ± 0.5 years and body mass index 23.3 ± 2.3 kg/m, who reported food intake during the last year and underwent videocapillaroscopy exams. The main outcome was the increase in functional capillary recruitment, that is, peak capillary density after post-occlusive reactive hyperemia subtracted from basal capillary density (caps/mm). Associations between reported food intake and functional capillary recruitment were investigated. Results: Daily average estimates of intake were: total energy (3,745 ± 1,365 kcal), carbohydrates (60.1 ± 5.9 %), lipids (22.1 ± 4.4 %), proteins (17.8 ± 4.1 %), fibers (33.9 ± 18.5 g), and cholesterol (492.8 ± 209.6 mg). Positive significant correlations with capillary recruitment were found for selenium (as μg/day/1,000 kcal; rho = 0.3412, p = 0.038,) calcium (as mg/day/1,000 kcal; rho = 0.3390, p = 0.043), and percentage of total energy from dairy products (rho = 0.3660, p = 0.023). Conclusions: Long-term intakes of selenium, calcium, and dairy products were positively associated with capillary recruitment in skin nutritive microcirculation in healthy young men. The role of such dietary components is discussed and possible mechanisms for their effects should be further investigated. This evidence adds one more possible functional property of these nutrients and food items. [ABSTRACT FROM AUTHOR]

Abstract: In this article, I will first give a brief account of my work at MGH on characterizing the intravascular susceptibility effect. Then I will describe studies into the underlying physiology of BOLD-fMRI which has become of interest to my group in the following decade. I will touch issues such as signal source of BOLD fMRI, capillary recruitment, the elusive initial dip and others. [Copyright &y& Elsevier]

Abstract: The cephalic phase of digestion (CPD) has been extensively investigated in terms of digestion and metabolism. Nevertheless, microcirculatory changes required to prepare peripheral tissues in order to dispose nutrients have never been assessed. In this study, microvascular function has been evaluated to determine its behavior and potential association to hormonal secretions during CPD. Thirty-nine healthy male subjects, 23.4±0.5years (mean±SD) and BMI of 23.3±2.3kg/m2, were randomized into receiving cognitive-sensorial stimuli to elicit CPD (CPD group, n=20) or not (control group, n=19), after a 12-h overnight fast. Main outcomes were differences in resting and peak functional capillary density (FCD, cap/mm2); resting red blood cell velocity (RBCV), peak RBCV (RBCVmax) and time taken to reach it (TRBCVmax); peak flow and vasomotion, before and after CPD and their associations with insulin and/or pancreatic polypeptide (PP). In the CPD group, basal FCD (24.9±7.6 to 28.3±8.1, p =0.005), peak FCD (27.8±6.3 to 32.6±7.1, p =0.002), RBCV (0.306±0.031 to 0.330±0.027mm/s, p =0.005), RBCVmax (0.336±0.029 to 0.398±0.292mm/s, p =0.005) and peak flow (23.5±14.3 to 26.9±15.8 PU, p <0.01) increased while TRBCVmax decreased (4.9±1.5 to 3.5±1.2s, p =0.01). No significant changes could be detected in the control group. Groups have not presented differences for insulin, but PP significantly increased in the CPD group and was positively associated to basal FCD increase (rho=0.527, p =0.03). In conclusion, neurally-mediated anticipatory responses of digestion elicited functional capillary recruitment associated to PP in healthy men, suggesting a precocious role for microcirculation in the physiology of digestion and nutrient homeostasis. [Copyright &y& Elsevier]

BACKGROUND Insulin resistance, i.e. impaired insulin-mediated glucose uptake (IMGU), is a major risk factor for type 2 diabetes in women with polycystic ovary syndrome (PCOS). Insulin-induced capillary recruitment (IICR) is considered a significant determinant of IMGU. We investigated whether IICR is a determinant IMGU in obese and lean women with and without PCOS. METHODS The study included 36 women with PCOS (20 lean, BMI 21.9 ± 2.3 kg/m2 and 16 obese, BMI 35.9 ± 6.0 kg/m2) and 27 age-matched healthy controls (14 lean, BMI 22.2 ± 1.8 kg/m2 and 13 obese, BMI 40.5 ± 7.0 kg/m2). IICR was evaluated by capillary microscopy during an isoglycemic-hyperinsulinemic clamp. IMGU was expressed as M/I value. RESULTS The M/I value was significantly lower in obese PCOS women compared with obese controls [0.5 (0.2–1.1) versus 0.8 (0.3–1.4) (mg kg−1 min−1 pmol l−1) × 100, P < 0.01], whereas the small difference between lean PCOS and lean control women was non-significant [1.5 (0.5–2.6) versus 1.7 (1.0–3.7) (mg kg−1 min−1 pmol l−1) × 100, P = 0.17]. Hyperinsulinemia increased capillary recruitment in lean controls (53.5 ± 20.3 versus 64.9 ± 27.4 n/mm2, P < 0.05), but not in either PCOS group nor in obese controls. IICR and androgens were a determinant of M/I value only in lean women with or without PCOS. CONCLUSIONS PCOS per se is associated with impaired IICR. Obese women with PCOS, in part independent of obesity, demonstrated a profound insulin resistance, whereas the difference between lean PCOS women and healthy controls was small and statistically non-significant. IICR was a determinant of IMGU in lean, but not in obese, women regardless of the presence of PCOS. [ABSTRACT FROM PUBLISHER]

We employed and evaluated a new application of contrast-enhanced ultrasound for real-time imaging of changes in microvascular blood volume (MBV) in tissues in females, males, and rat. Continuous real-time imaging was performed using contrast-enhanced ultrasound to quantify infused gas-filled microbubbles in the microcirculation. It was necessary to infuse microbubbles for a minimum of 5-7 min to obtain steady-state bubble concentration, a prerequisite for making comparisons between different physiological states. Insulin clamped at a submaximal concentration (∼75 μU/ml) increased MBV by 27 and 39% in females and males, respectively, and by 30% in female subcutaneous adipose tissue. There was no difference in the ability of insulin to increase muscle MBV in females and males, and microvascular perfusion rate was not increased significantly by insulin. However, perfusion rate of the microvascular space was higher in females compared with males. In rats, insulin clamped at a maximal concentration increased muscle MBV by 60%. Large increases in microvascular volume and perfusion rate were detected during electrical stimulation of muscle in rats and immediately after exercise in humans. We have demonstrated that real-time imaging of changes in MBV is possible in human and rat muscle and in subcutaneous adipose tissue and that the method is sensitive enough to pick up relatively small changes in MBV when performed with due consideration of steady-state microbubble concentration. Because of real-time imaging, the method has wide applications for determining MBV in different organs during various physiological or pathophysiological conditions. [ABSTRACT FROM AUTHOR]

Type 2 diabetes is in essence a vascular disease and is frequently associated with hypertension, macrovascular events, and microvascular complications. Microvascular dysfunction, including impaired recruitment and capillary rarefaction, has been implicated in the pathogenesis of diabetic complications. Microvascular insulin resistance and renin-angiotensin system upregulation are present in diabetes, and each contributes to the development of hypertension and microvascular dysfunction. In the insulin-sensitive state, insulin increases microvascular perfusion by increasing endothelial nitric oxide production, but this effect is abolished by insulin resistance. Angiotensin II, acting via the type 1 receptors, induces inflammation and oxidative stress, leading to impaired insulin signaling, reduced nitric oxide availability, and vasoconstriction. Conversely, it acts on the type 2 receptors to cause vasodilatation. Because substrate and hormonal exchanges occur in the microvasculature, antihypertensive agents targeted to improve microvascular insulin sensitivity and function may have beneficial effects beyond their capacity to lower blood pressure in patients with diabetes. [ABSTRACT FROM AUTHOR]