Cutaneous Microvascular Function Research Articles

NADPH oxidase-derived reactive oxygen species contribute to impaired cutaneous microvascular function in chronic kidney disease.

Oxidative stress promotes vascular dysfunction in chronic kidney disease (CKD). We utilized the cutaneous circulation to test the hypothesis that reactive oxygen species derived from NADPH oxidase and xanthine oxidase impair nitric oxide (NO)-dependent cutaneous vasodilation in CKD. Twenty subjects, 10 stage 3 and 4 patients with CKD (61 ± 4 yr; 5 men/5 women; eGFR: 39 ± 4 ml·min(-1)·1.73 m(-2)) and 10 healthy controls (55 ± 2 yr; 4 men/6 women; eGFR: >60 ml·min(-1)·1.73 m(-2)) were instrumented with 4 intradermal microdialysis fibers for the delivery of 1) Ringer solution (Control), 2) 10 μM tempol (scavenge superoxide), 3) 100 μM apocynin (NAD(P)H oxidase inhibition), and 4) 10 μM allopurinol (xanthine oxidase inhibition). Skin blood flow was measured via laser-Doppler flowmetry during standardized local heating (42°C). N(g)-nitro-l-arginine methyl ester (L-NAME; 10 mM) was infused to quantify the NO-dependent portion of the response. Cutaneous vascular conductance (CVC) was calculated as a percentage of the maximum CVC achieved during sodium nitroprusside infusion at 43°C. Cutaneous vasodilation was attenuated in patients with CKD (77 ± 3 vs. 88 ± 3%, P = 0.01), but augmented with tempol and apocynin (tempol: 88 ± 2 (P = 0.03), apocynin: 91 ± 2% (P = 0.001). The NO-dependent portion of the response was reduced in patients with CKD (41 ± 4 vs. 58 ± 2%, P = 0.04), but improved with tempol and apocynin (tempol: 58 ± 3 (P = 0.03), apocynin: 58 ± 4% (P = 0.03). Inhibition of xanthine oxidase did not alter cutaneous vasodilation in either group (P > 0.05). These data suggest that NAD(P)H oxidase is a source of reactive oxygen species and contributes to microvascular dysfunction in patients with CKD.

Impact of natural cocoa ingestion on microvascular endothelial function in healthy older adults (1156.10)

Impact of natural cocoa ingestion on microvascular endothelial function in healthy older adults Michelle L. Harrison1, Kevin M. Christmas1, Amy G. Preston2, Stephen J. Crozier2, R. Matthew Brothers1 1Environmental and Autonomic Physiology Laboratory, Department of Kinesiology and Health Education, University of Texas at Austin; 2The Hershey Company, Hershey, Pennsylvania Aging is associated with a progressive decline in endothelial function that is significantly correlated with increased cardiovascular disease risk. The objective of this study is to investigate the role of natural cocoa (NC) on cutaneous microvascular endothelial function in older individuals. The skin represents an easily accessible vascular bed and evidence is suggesting that changes in the microcirculation may precede overt clinical signs of disease. This study is testing the hypothesis that older individuals will exhibit impaired thermal reactivity in response to a local heating stimulus and that this impairment will be restored following acute NC ingestion (13g NC, The Hershey Company). 11 individuals (68±5 years) were tested on two separate days; they were provided either a NC‐free placebo or a NC‐containing beverage (randomized order, double‐blinded). Cutaneous vascular conductance (CVC) was assessed while the skin was clamped at 34°C and 40°C and values were normalized to a maximal value obtained during 43°C heating for 30 min. This was done pre and 2 hours post NC ingestion. There is a trend for post‐CVC to be increased following flavanol ingestion at both 34°C (Pre: 11±3 % max vs. Post: 14±5 % max; P=0.08) and 40°C (Pre: 58±10 % max vs. Post: 64±14 % max; P=0.10). Our preliminary data suggest that microvascular endothelial function may be improved in older individuals following acute NC ingestion.

Apocynin and tempol restores cutaneous microvascular function in healthy, salt‐resistant adults on a high sodium diet (LB686)

The purpose of this study was to determine if NADPH derived superoxide plays a role in attenuating cutaneous vasodilation in response to local heating in healthy, salt‐resistant adults on a high sodium diet. Nineteen healthy adults (33±3yrs) participated in a controlled feeding study. Subjects completed 7 days of a low sodium (LS) diet (20mmol sodium/day) and 7 days of a high sodium (HS) diet (300mmol sodium/day) in random order. On the final day of LS and HS diets cutaneous microvascular function was assessed using a standard heating protocol. RBC flux was measured via laser Doppler flowmetry coupled with interdermal microdialysis for the local delivery of 10µM tempol (scavenging superoxide) and 100 µM apocynin (inhibiting NADPH oxidase). Once a stable post‐heating plateau was achieved, 10mM L‐NAME was infused through all sites to determine NO contribution to vasodilation. The plateau phase of cutaneous vasodilation was attenuated in the HS condition compared to LS (91.0±1.8 vs 83.4±1.9; p<0.05) and was restored with the local infusion of both tempol and apocynin (p<0.05). The NO contribution to cutaneous vasodilation was also decreased on the HS diet compared to LS (62.7±4.2 vs 52.3±4.6; p<0.05). This was restored with the infusion of apocynin (p< 0.05) but was not improved by tempol (p=0.173). These finding suggest that NADPH derived superoxide plays a role in dietary sodium induced decreases in cutaneous vasodilation in response to local heating.Grant Funding Source: Supported by NIH Grant R01 HL104106‐01A1

Urine π-Glutathion S-transferase but not Tamm-Horsfall protein correlates with Carotid artery intima media thickness in childhood type1 diabetes

BackgroundRenal disease remains a serious threat in patients with insulin-dependent (type1) diabetes. Hence its detection early in the life of patients with type1 diabetes is crucial. Several lines of evidence suggest similar mechanisms for the development of both renal and arterial disease. We sought to investigate in young patients with type1 diabetes whether π-Glutathione S-transferase to creatinine (π-GST:crea) and Tamm-Horsfall protein to creatinine (THP:crea) ratios, markers of distal tubular renal function, relate to subclinical markers of arterial disease, which appear to onset early and develop rapidly in type1 diabetes.MethodsSeventy-one children and adolescents (median age and diabetes duration 14 and 6 years, respectively) with type1 diabetes for at least 6 months were assessed for timed urine levels of π-GST, THP, HbA1c, albumin, and plasma C-reactive protein (CRP). Carotid artery intima-media thickness (IMT), brachial artery flow-mediated dilatation (FMD), and cutaneous microvascular function were assessed by high-resolution ultrasound and laser Doppler, respectively.ResultsTwo patients had microalbuminuria (> 20 μg/min), and were therefore removed from the study population. π-GST:crea ratio and THP:crea showed no relationship to the demographic, diabetes, or inflammatory indices. Lower π-GST:crea ratio was associated with greater IMT (p = 0.01, r = −0.29), particularly in female patients (p = 0.004, r = −0.49). The association of π-GST:crea ratio with IMT was stronger in patients with passive smoke exposure (p = 0.002, r = −0.43). Among post-pubertal patients, lower π-GST:crea ratio was also associated with lower microvascular response to Ach (acetylcholine; p = 0.03, r = 0.49).ConclusionsIn young patients with type1 diabetes, proximal tubular dysfunction as suggested by lower levels of π-GST:crea ratio seems to be paralleled by changes in arterial structure and microvascular function.

Acute hyperglycaemia does not alter nitric oxide-mediated microvascular function in the skin of adolescents with type 1 diabetes

We assessed the impact of an acute bout of hyperglycaemia on nitric oxide (NO)-mediated microvascular function in the skin of adolescents with type 1 diabetes (T1DM). Twelve subjects (12-18 years) with T1DM were randomised into a control (n = 6) or hyperglycaemia (n = 6) group. Hyperinsulinaemic clamps were used to manipulate blood glucose level (BGL). Following a baseline period, where all subjects were euglycaemic (20 min), the experimental phase began. During the experimental phase, BGL was elevated to 16.7 ± 0.9 mmol L(-1) in the hyperglyceamic group, while it was maintained at euglycaemia (5.5 ± 0.1 mmol L(-1)) in the control group. Simultaneously, cutaneous microvascular function (% max cutaneous vascular conductance, CVC%) was assessed using laser Doppler fluxometry following stimulation of skin blood flow using localised heating (42 °C). To determine the NO contribution to skin blood flow, two microdialysis sites were assessed, one perfused with Ringers and the other with the NO blocker, NG-monomethyl-L-arginine (L-NMMA). In the hyperglycaemic group, acute increase in BGL was not associated with changes in skin blood flow (CVC% 82.4 ± 8.7% at 5.5 ± 0.1 mmol L(-1) vs 79.5 ± 9.1% at 16.7 ± 0.9 mmol L(-1), unpaired t tests, P = 0.588) or the contribution of NO to vasodilation. These results suggest that, in our group of adolescents with type 1 diabetes, acute hyperglycaemia did not affect skin microvascular NO-mediated function.

Effect of decompression-induced bubble formation on highly trained divers microvascular function

We previously showed microvascular alteration of both endothelium-dependent and -independent reactivity after a single SCUBA dive. We aimed to study mechanisms involved in this postdive vascular dysfunction. Ten divers each completed three protocols: (1) a SCUBA dive at 400 kPa for 30 min; (2) a 41-min duration of seawater surface head immersed finning exercise to determine the effect of immersion and moderate physical activity; and (3) a simulated 41-min dive breathing 100% oxygen (hyperbaric oxygen [HBO]) at 170 kPa in order to analyze the effect of diving-induced hyperoxia. Bubble grades were monitored with Doppler. Cutaneous microvascular function was assessed by laser Doppler. Endothelium-dependent (acetylcholine, ACh) and -independent (sodium nitroprusside, SNP) reactivity was tested by iontophoresis. Endothelial cell activation was quantified by plasma Von Willebrand factor and nitric oxide (NO). Inactivation of NO by oxidative stress was assessed by plasma nitrotyrosine. Platelet factor 4 (PF4) was assessed in order to determine platelet aggregation. Blood was also analyzed for measurement of platelet count. Cutaneous vascular conductance (CVC) response to ACh delivery was not significantly decreased by the SCUBA protocol (23 ± 9% before vs. 17 ± 7% after; P = 0.122), whereas CVC response to SNP stimulation decreased significantly (23 ± 6% before vs. 10 ± 1% after; P = 0.039). The HBO and immersion protocols did not affect either endothelial-dependent or -independent function. The immersion protocol induced a significant increase in NO (0.07 ± 0.01 vs. 0.12 ± 0.02 μg/mL; P = 0.035). This study highlighted change in microvascular endothelial-independent but not -dependent function in highly trained divers after a single air dive. The results suggest that the effects of decompression on microvascular function may be modified by diving acclimatization.

Abstract 209: NAD(P)H Oxidase-Derived Superoxide Contributes to Impaired Cutaneous Microvascular Function in Chronic Kidney Disease

Endothelial dysfunction occurs in chronic kidney disease (CKD) and cardiovascular disease is the most common cause of death in these patients. Oxidative stress has been shown to be a mechanism of vascular dysfunction in CKD. We utilized the cutaneous circulation to test the hypothesis that superoxide derived from NAD(P)H oxidase and xanthine oxidase impair nitric oxide (NO)-dependent cutaneous vasodilation patients with CKD. Twenty subjects, 10 stage 3 and 4 CKD patients (61±4 years; 5 male/5 female; eGFR: 39 ± 4 ml·min -1 ·1.73m -2 ) and 10 healthy controls (HC) (55±2 years; 4 male/6 female; eGFR: >60 ml·min -1 ·1.73m -2 ) were instrumented with 4 intradermal microdialysis fibers in the forearm for the local delivery of 1) Ringers solution (Control), 2) 10 μM Tempol to scavenge superoxide, 3) 100 μM apocynin to inhibit NAD(P)H oxidase, and 4) 10 μM allopurinol to inhibit xanthine oxidase. Red blood cell (RBC) flux was measured via laser Doppler flowmetry during standardized local heating (42°C). After the local heating response was established, 10 mM L-NAME was infused into all four sites to quantify the NO-dependent portion of the response. Cutaneous vascular conductance (CVC) was calculated as RBC flux/mean arterial pressure and all data are presented as a percentage of maximum CVC achieved during 28mM sodium nitroprusside infusion at 43°C. The plateau in cutaneous vasodilation was attenuated in CKD at the control site (CKD: 77±3 vs. HC: 88±3 %, p<0.05). Tempol and apocynin augmented the plateau in cutaneous vasodilation in CKD patients (Tempol: 88±2, apocynin: 91±2 %, p<0.05 vs. CKD control site) but had no effect in the healthy control group. The NO-dependent portion of the response was reduced in CKD at the control site (CKD: 41±4 vs. HC: 58±2 %, p<0.05). Tempol and apocynin augmented NO-dependent portion of the response in CKD patients (Tempol: 58±3, apocynin: 58±4 %, p<0.05 vs. CKD control site) but had no effect in the healthy control group. Inhibition of xanthine oxidase did not alter the plateau in cutaneous vasodilation in either group (p>0.05). These data suggest that NAD(P)H oxidase is a source of superoxide and contributes to microvascular dysfunction in CKD.

Laser doppler-assessed cutaneous microvascular function in cardiac syndrome x patients

Laser doppler-assessed cutaneous microvascular function in cardiac syndrome x patients

Oral clopidogrel improves cutaneous microvascular function through EDHF-dependent mechanisms in middle-aged humans

Platelet P₂Y₁₂-ADP and COX-1 receptor inhibition with oral clopidogrel (CLO) and low-dose aspirin (ASA), respectively, attenuates reflex-mediated cutaneous vasodilation, but little is known about how these medications affect local vasodilatory signaling. Reactive hyperemia (RH) results in vasodilation that is mediated by sensory nerves and endothelium-derived hyperpolarization factors (EDHF) through large-conductance calcium-activated potassium channels, whereas slow local heating (LH) elicits vasodilation largely through the production of nitric oxide (NO). We hypothesized that CLO and ASA would attenuate locally mediated cutaneous vasodilation assessed by RH and LH (0.5°C/min). In a randomized, cross-over, double-blind placebo-controlled study, nine healthy men and women (56 ± 1 yr) took CLO (75 mg), ASA (81 mg), and placebo for 7 days. Skin blood flow was measured (laser-Doppler flowmetry, LDF) and cutaneous vascular conductance (CVC) was calculated (LDF/mean arterial pressure) and normalized to maximal CVC (%CVCmax: 43°C and 28 mM sodium nitroprusside). RH response parameters, including area under the curve (AUC), total hyperemic response (THR), and the decay constant tau (λ) were calculated. NO-dependent vasodilation during LH was assessed by calculating the difference in %CVCmax between a control site and an NO synthase-inhibited site (10 mM l-NAME: intradermal microdialysis). CLO augmented the AUC and THR (AUCclo = 3,783 ± 342; THRclo = 2,306 ± 266% CVCmax/s) of the RH response compared with ASA (AUCASA = 3,101 ± 325; THRASA = 1,695 ± 197% CVCmax/s) and placebo (AUCPlacebo = 3,000 ± 283; THRPlacebo = 1,675 ± 170% CVCmax/s; all P < 0.0001 vs. CLO). There was no difference in the LH response or calculated NO-dependent vasodilation among treatments (all P > 0.05). Oral CLO treatment augments vasodilation during RH but not LH, suggesting that CLO may improve cutaneous microvascular function.

Exercise training improves cutaneous microvascular function in nonalcoholic fatty liver disease

The leading causes of mortality in nonalcoholic fatty liver disease (NAFLD) relate to cardiovascular disease (CVD). The contribution of nitric oxide (NO) to endothelial function, a surrogate of CVD risk, is currently unknown in NAFLD. We hypothesize that NO-mediated cutaneous microvessel function would be impaired in NAFLD compared with controls and that exercise would enhance microvessel function compared with conventional care. Thirteen NAFLD patients (aged 50 ± 3 yr, BMI 31 ± 1 kg/m²) and seven controls (48 ± 4 yr, 30 ± 2 kg/m²) were studied. NAFLD patients were randomized to either 16 wk of exercise or conventional care. Cutaneous microvessel function was examined using laser Doppler flowmetry combined with intradermal microdialysis of N(G)-monomethyl-l-arginine to assay the NO dilator response to local forearm heating. Magnetic resonance imaging and spectroscopy quantified abdominal and liver fat, respectively, and cardiorespiratory fitness was assessed. Differences in NO contribution to cutaneous blood flow between NAFLD and control individuals and between interventions were analyzed using general linear modeling. NO contribution to cutaneous blood flow was similar between NAFLD and controls (P = 0.47). Cardiorespiratory fitness was greater following exercise training compared with conventional care. NO contribution to cutaneous blood flow in response to heating at 42°C was 20.4% CVCmax (95% CI = 4.4, 36.4) greater following exercise training compared with conventional care (P = 0.02). Exercise training improves cutaneous microvascular NO function in NAFLD patients. The benefit of exercise training compared with conventional care strongly supports a role for exercise in the prevention of CVD in NAFLD.

P70: Molecular and physiological aspects connecting red cell eNOS, red blood cell deformability and decreased microvascular function in patients with essential hypertension

Background Arterial hypertension (HT) is a complex multifactorial condition associated with cardiovascular disease. Independent studies show that HT is associated with microcirculatory and hemorheological alterations, such as decreased red blood cell (RBC) deformability, as well as decreased endothelial function and nitric oxide (NO) bioavailability. Recently we found RBC carry an active endothelial nitric oxide synthase (eNOS), which is decreased in cardiovascular disease.Hypothesis: We hypothesized that a reduced RBC deformability may contribute to induce a hypertensive phenotype via impairment of microcirculatory conductance. Methods To evaluate hemorehological alterations in HT, patients ( n = 10) with HT and age-and risk factors-matched subjects ( n = 10) without HT (control) were recruited. High BP was defined as systolic BP > 135 mm Hg and diastolic BP > 85 mm in 24 h BP measurements. RBC deformability was measured by laser-assisted optical rotational cell analyzer (LORCA) and assessed as elongation index (EI) at 1.73 Pa. RBC redox state (ROS, GSH) was assessed by labeling with diclorodihydrofluorescein and thiol-tracker and flow cytometry. Cutaneous microvascular function as post-occlusion reactive hyperemia was measured by noninvasive laser Doppler Perfusion imaging and quantified as area under the curve (AUC). Endothelial function of the brachial artery was assessed as flow-mediated dilatation (FMD) by high resolution ultrasound. Deformability of RBC from eNOS −/− mice was evaluated and compared to wild type (WT) C57Bl/6 mice. To evaluate NO and NOS-dependent changes in RBC deformability, RBC from healthy individuals ( n = 6) were treated with NO donors, NOS inhibitors and guanylate cyclase inhibitors. Measurements of cGMP production in RBC were assessed by ELISA. A stepwise linear regression as well as a multivariate linear regression model were performed to identify independent predictors for systolic BP. Results In the HT group EI (0.300 ± 0.007 vs. 0.326 ± 0.007, p = 0.013), AUC (1657 ± 422 vs. 2313 ± 473 PU; p = 0.009). and FMD (6.2% ± 0.7% vs. 5.0% ± 0.3 % p = 0.010) was reduced in the HT group, suggesting decreased deformability, shorter lasting vasodilation of microvessels and endothelial dysfunction. In RBC from HT patients the ROS levels increased and the GSH levels decreased, indicating increased oxidative stress. Univariate inverse correlations were found between systolic BP and AUC ( r = −0.485; p r = 0.726; p R 2 = 0.607, p = 0.004). In a translational approach we analyzed deformability in eNOS −/− mice, characterized by a dysfunctional endothelium and hypertension. eNOS −/− RBC are less deformable than WT RBC, show increased ROS and decreased GSH, similarly to the HT grouP Moreover, NO donors increased EI of RBC from healthy individuals, while NOS inhibition as well as guanlyte cyclase inhibition decreased cGMP levels and EI indicating that NO/NOS/cGMP dependent pathways control deformability in RBC. Conclusion The NO/NOS/cGMP pathway controls RBC mechanoproperties, and RBC deformability is an independent predictor of increased blood pressure in patients with arterial hypertension. Disclosure Nothing to disclose.

Nitric oxide‐mediated cutaneous microvascular function is impaired in polycystic ovary sydrome but can be improved by exercise training

Polycystic ovary syndrome (PCOS) is associated with cardiovascular disease. The contribution of the nitric oxide (NO) dilator system to cutaneous endothelial dysfunction is currently unknown in PCOS. Our aim was to examine whether women with PCOS demonstrate impaired cutaneous microvascular NO function and whether exercise training can ameliorate any impairment. Eleven women with PCOS (age, 29 ± 7 years; body mass index, 34 ± 6 kg m(-2)) were compared with six healthy obese control women (age, 29 ± 7 years; body mass index, 34 ± 5 kg m(-2)). Six women with PCOS (30 ± 7 years; 31 ± 6 kg m(-2)) then completed 16 weeks of exercise training. Laser Doppler flowmetry, combined with intradermal microdialysis of l-N(G)-monomethyl-l-arginine, a nitric oxide antagonist, in response to incremental local heating of the forearm was assessed in women with PCOS and control women, and again in women with PCOS following exercise training. Cardiorespiratory fitness, homeostasis model assessment for insulin resistance, hormone and lipid profiles were also assessed. Differences between women with PCOS and control women and changes with exercise were analysed using Student's unpaired t tests. Differences in the contribution of NO to cutaneous blood flow [expressed as a percentage of maximal cutaneous vasodilatation (CVCmax)] were analysed using general linear models. At 42°C heating, cutaneous NO-mediated vasodilatation was attenuated by 17.5%CVCmax (95% confidence interval, 33.3, 1.7; P = 0.03) in women with PCOS vs. control women. Exercise training improved cardiorespiratory fitness by 5.0 ml kg(-1) min(-1) (95% confidence interval, 0.9, 9.2; P = 0.03) and NO-mediated cutaneous vasodilatation at 42°C heating by 19.6% CVCmax (95% confidence interval, 4.3, 34.9; P = 0.02). Cutaneous microvascular NO function is impaired in women with PCOS compared with obese matched control women but can be improved with exercise training.

Sodium loading and cutaneous microvascular function: more than skin deep

For several years the human cutaneous circulation has been utilized as a representative vascular bed to assess microvascular function in clinical and pre-disease model populations. With relevance to hypertension, deficits in cutaneous microvascular function are related to impairment in indices of renal vascular function and target organ damage (Coulon et al. 2011). While the skin serves mainly thermoregulatory purposes, several skin-specific methodologies including both thermal and pharmacological stimuli and interventions have been successfully utilized to pharmacodissect underlying mechanisms of vascular dysfunction (Holowatz et al. 2008). The most commonly explored signalling pathways in human skin most relevant to globalized vascular dysfunction are nitric oxide synthase (NOS)-dependent vasodilatory mechanisms, and noradrenaline-mediated vasoconstrictor mechanisms. Moreover, specific pathology-relevant oxidant stress mechanisms have been explored using both specific and non-specific antioxidants including allopurinol, apocynin and ascorbate (Medow et al. 2011). In this issue of The Journal of Physiology, Greaney et al. (2012) published an elegant study examining the effects of dietary sodium loading on microvascular function, independent of an increase in blood pressure. This study is the first to show that dietary sodium loading in normotensive salt-resistant humans impairs cutaneous eNOS-dependent vasodilatation utilizing a local skin heating stimulus. Furthermore, when the non-specific antioxidant ascorbate was locally delivered, eNOS-dependent vasodilatation was restored. Together, the data from Greaney et al. show that dietary sodium-induces decrements in cutaneous microvascular function that occur through ascorbate-sensitive oxidant stress mechanisms. The results from this study bring to light several interesting points to consider from both a globalized vascular health perspective and for methodological reasons when examining the neurovascular regulation of skin blood flow. Human skin has been used as a model for examining decrements in vascular function with hypertension-induced vascular pathology for several decades. While as a regional circulation the compliant cutaneous circulation contributes minimally to the increase in systemic vascular resistance in comparison to more nutritive vascular beds, decrements in microvascular function are clearly apparent. Even before the technology was available to image or measure more precise changes in microcirculatory function through laser-Doppler or laser-speckle imagery, Carberry et al. (1992) utilized venous occlusion plethysmography and a whole limb heating technique to show that subjects with essential hypertension have lower forearm blood flows to increasing temperature and lower maximal blood flow, indicating a degree of endothelial dysfunction and inward vessel remodelling. Moreover, progressive decrements in vascular function to endothelium-dependent agonists with the severity of hypertensive disease have been consistently observed (Farkas et al. 2004). More recently with the development of skin-specific methodologies the underlying mechanisms of hypertension-induced vascular dysfunction are being extensively explored (Smith et al. 2011). The study by Greaney et al. adds another piece to the puzzle suggesting that dietary salt loading alone without increases in mean arterial pressure induces changes in vascular function that are consistent with a pre-clinical hypertensive vascular pathology state. From a methodological perspective, the results from Greaney et al. highlight the need for cautious experimental controls in all studies examining the neurovascular regulation of skin blood flow whether in healthy or clinical populations. Controlling or documenting sodium intake in human subjects may be a necessary experimental control especially when examining clinical populations. Finally, meaningful physiological interpretations of studies like that of Greaney et al. are not possible without tightly controlled mechanistic work in healthy populations. More of this work is necessary so that clinical test of microvascular function in the skin can be utilized on a broader scale (Minson, 2010).

Dietary sodium loading impairs microvascular function independent of blood pressure in humans: role of oxidative stress

Animal studies have reported dietary salt-induced reductions in vascular function independent of increases in blood pressure (BP). The purpose of this study was to determine if short-term dietary sodium loading impairs cutaneous microvascular function in normotensive adults with salt resistance. Following a control run-in diet, 12 normotensive adults (31 ± 2 years) were randomized to a 7 day low-sodium (LS; 20 mmol day(-1)) and 7 day high-sodium (HS; 350 mmol day(-1)) diet (controlled feeding study). Salt resistance, defined as a 5 mmHg change in 24 h mean BP determined while on the LS and HS diets, was confirmed in all subjects undergoing study (LS: 84 ± 1 mmHg vs. HS: 85 ± 2 mmHg; P > 0.05). On the last day of each diet, subjects were instrumented with two microdialysis fibres for the local delivery of Ringer solution and 20 mm ascorbic acid (AA). Laser Doppler flowmetry was used to measure red blood cell flux during local heating-induced vasodilatation (42°C). After the established plateau, 10 mm l-NAME was perfused to quantify NO-dependent vasodilatation. All data were expressed as a percentage of maximal cutaneous vascular conductance (CVC) at each site (28 mm sodium nitroprusside; 43°C). Sodium excretion increased during the HS diet (P < 0.05). The plateau % CVCmax was reduced during HS (LS: 93 ± 1 % CVCmax vs. HS: 80 ± 2 % CVCmax; P < 0.05). During the HS diet, AA improved the plateau % CVCmax (Ringer: 80 ± 2 % CVCmax vs. AA: 89 ± 3 % CVCmax; P < 0.05) and restored the NO contribution (Ringer: 44 ± 3 % CVCmax vs. AA: 59 ± 6 % CVCmax; P < 0.05). These data demonstrate that dietary sodium loading impairs cutaneous microvascular function independent of BP in normotensive adults and suggest a role for oxidative stress.

Peripheral vascular response to inspiratory breath hold in paediatric homozygous sickle cell disease

New Findings• What is the central question of this study?Autonomic nervous dysfunction is implicated in complications of sickle cell anaemia (SCA). In healthy adults, a deep inspiratory breath hold (IBH) elicits rapid transient SNS- mediated vasoconstriction detectable using Laser Doppler Flux (LDF) assessment of the finger-tip cutaneous micovasculature.• What is the main finding and its importance?We demonstrate significantly increased resting peripheral blood flow and sympathetic activity in African children with SCA compared to sibling controls and increased sympathetic stimulation in response to vasoprovocation with DIG.This study is the first to observe an inverse association between resting peripheral blood flow and haemoglobin oxygen saturation (SpO2). These phenomena may be an adaptive response to the hypoxic exposure in SCA.There is increasing evidence that autonomic dysfunction in adults with homozygous sickle cell (haemoglobin SS) disease is associated with enhanced autonomic nervous system-mediated control of microvascular perfusion. However, it is unclear whether such differences are detectable in children with SS disease. We studied 65 children with SS disease [38 boys; median age 7.2 (interquartile range 5.1–10.6) years] and 20 control children without symptoms of SS disease [8 boys; 8.7 (5.5–10.8) years] and recorded mean arterial blood pressure (ABP) and daytime haemoglobin oxygen saturation (). Cutaneous blood flux at rest (RBF) and during the sympathetically activated vasoconstrictor response to inspiratory breath hold (IBH) were measured in the finger pulp of the non-dominant hand using laser Doppler fluximetry. Local factors mediating flow motion were assessed by power spectral density analysis of the oscillatory components of the laser Doppler signal. The RBF measured across the two study groups was negatively associated with age (r=−0.25, P < 0.0001), ABP (r=−0.27, P= 0.02) and daytime (r=−0.30, P= 0.005). Children with SS disease had a higher RBF (P= 0.005) and enhanced vasoconstrictor response to IBH (P= 0.002) compared with control children. In children with SS disease, higher RBF was associated with an increase in the sympathetic interval (r=−0.28, P= 0.022). The SS disease status, daytime and age explained 22% of the variance in vasoconstrictor response to IBH (P < 0.0001). Our findings suggest that blood flow and blood flow responses in the skin of young African children with SS disease differ from those of healthy control children, with increased resting peripheral blood flow and increased sympathetic stimulation from a young age in SS disease. They further suggest that the laser Doppler flowmetry technique with inspiratory breath hold manoeuvre appears to be robust for use in young children with SS disease, to explore interactions between , ABP and autonomic function with clinical complications, e.g. skin ulceration.

Exercise training improves cutaneous microvascular nitric oxide dysfunction in women with polycystic ovarian syndrome

Polycystic ovarian syndrome (PCOS) is associated with increased risk of cardiovascular disease (CVD). Microvascular function contributes to hypertension by raising peripheral vascular resistance and arterial stiffness. The contribution of nitric oxide (NO) to cutaneous microvascular function in PCOS has not been explored.

Obstructive Sleep Apnea and Diabetic Neuropathy

Diabetic peripheral neuropathy is common and causes significant morbidity. Obstructive sleep apnea (OSA) is also common in patients with type 2 diabetes. Because OSA is associated with inflammation and oxidative stress, we hypothesized that OSA is associated with peripheral neuropathy in type 2 diabetes. To assess the relationship between OSA and peripheral neuropathy in patients with type 2 diabetes. A cross-sectional study of adults with type 2 diabetes recruited randomly from the diabetes clinic of two UK hospitals. Peripheral neuropathy was diagnosed using the Michigan Neuropathy Screening Instrument. OSA (apnea-hypopnea index ≥ 5 events/h) was assessed using home-based, multichannel respiratory monitoring. Serum nitrotyrosine was measured by ELISA, lipid peroxide by spectrophotometer, and microvascular function by laser speckle contrast imaging. Two hundred thirty-four patients (mean [SD] age, 57 [12] yr) were analyzed. OSA prevalence was 65% (median apnea-hypopnea index, 7.2; range, 0-93), 40% of which were moderate to severe. Neuropathy prevalence was higher in patients with OSA than those without (60% vs. 27%, P < 0.001). After adjustment for possible confounders, OSA remained independently associated with diabetic neuropathy (odds ratio, 2.82; 95% confidence interval, 1.44-5.52; P = 0.0034). Nitrotyrosine and lipid peroxide levels (n = 102, 74 with OSA) were higher in OSA and correlated with hypoxemia severity. Cutaneous microvascular function (n = 71, 47 with OSA) was impaired in OSA. We describe a novel independent association between diabetic peripheral neuropathy and OSA. We identified increased nitrosative/oxidative stress and impaired microvascular regulation as potential mechanisms. Prospective and interventional studies are needed to assess the impact of OSA and its treatment on peripheral neuropathy development and progression in patients with type 2 diabetes.

Acute dietary salt loading impairs cutaneous microvascular function in normotensive salt‐resistant adults: role of oxidative stress

Animal studies have reported dietary salt‐induced reductions in vascular function without an increase in blood pressure (BP). The purpose of this study was to determine if acute dietary salt loading impairs cutaneous microvascular function in normotensive adults with salt‐resistant BP. Following a control run‐in diet, 10 normotensive salt‐resistant subjects (31±3 yr) were randomized to a 7 day high salt (HS; 350 mmol/day) and 7 day low salt (LS; 20 mmol/day) diet (controlled feeding study). Salt‐resistant BP was defined as a change in 24‐hour mean BP of ≤ 5 mmHg from the LS to the HS diet. On the last day of each diet, subjects were instrumented with three microdialysis fibers for the local delivery of Ringer's solution (R), 10 mM L‐NAME, and 20 mM ascorbic acid (AA). Laser Doppler flowmetry was used to measure red blood cell flux during local heating (42□). All data were expressed as a percentage of the maximum cutaneous vascular conductance (CVC) at each site (28 mM SNP; 43□). The plateau %CVCmax was reduced during HS (LS 93±1 v. HS 80±2, P&lt;0.05), as was the nitric oxide (NO) contribution to the plateau (LS 55±5 v. HS 46±3, P=0.075). During HS, AA improved the plateau %CVCmax (R 80±2 v. AA 89±3, P&lt;0.05) and restored the NO contribution (R 46±3 v. AA 60±7, P&lt;0.05). These data suggest that acute dietary salt loading impairs cutaneous microvascular function in normotensive salt‐resistant adults and indicate a role for oxidative stress.Supported by 2 P20 RR016472‐11 and HL104106.

Evaluation of systemic microvascular endothelial function using laser speckle contrast imaging

ObjectiveThe aim of this study was to compare cutaneous microvascular function in young healthy subjects (n=50) with that of cardiometabolic diseased patients (n=50) using laser speckle contrast imaging (LSCI) coupled with transdermal iontophoretic delivery of acetylcholine (ACh) and post-occlusive reactive hyperemia (PORH). MethodsCutaneous blood flow was assessed in the forearm using LSCI at rest, during PORH and during iontophoresis of ACh with increasing anodal currents of 30, 60, 90, 120, 150 and 180μA during 10-second intervals spaced 1min apart. ResultsEndothelium-dependent skin microvascular vasodilator responses induced by both ACh and PORH were significantly reduced in cardiometabolic diseased patients compared to healthy subjects. Vasodilator responses induced by ACh were significantly higher in young women than in young men. Iontophoresis charges up to 1.5mC do not induce nonspecific effects on skin microvascular flux. ConclusionLSCI appears to be a promising noninvasive technique for evaluating systemic microvascular endothelial function.

“Studying the cutaneous microcirculatory response during upper-limb exercise in healthy, older, sedentary people”

This study investigated changes incurred in cutaneous skin blood flux (SKBF) in the superficial veins of the lower limb by upper limb exercise training in the form of arm-cranking in 14 healthy participants over the age of 50 years. Changes in cutaneous microvascular function of the lower leg were assessed using laser Doppler Flowmetry (LDF) during a 30-minute exercise session undertaken over 4-exercise periods. Both SKBF and Time to reach Peak Perfusion (Tmax) were improved significantly during the 2nd (e.g. 121 (± 107.2) vs 280 (± 269.1) and 171 (± 34.4) vs. 247 (± 38.3) respectively) when compared to the first exercise period, while values approaching initial levels in the following stages. The results indicate that the thermoregulatory and vasodilation mechanisms observed during exercise in middle-aged and older healthy people are different to the one appearing in younger age groups, suggesting a more extensive effect of the age-related structural changes than it was previously thought.