Postischemic Reactive Hyperemia Research Articles

Sodium Loading Does Not Induce Oxidative Stress-Mediated Reductions in Vascular Function in Young Adults

Short-term, high sodium diets decrease dilation responses in conduit arteries and the microvasculature when compared to low sodium diets (e.g., 7000 vs. 500 mg/day). Supraphysiological antioxidant treatment mitigates these effects supporting a role for oxidative stress in sodium-induced vascular impairments. It is unclear whether these effects are present when high sodium conditions are compared to the sodium level of a typical American diet (~3400 mg/day). Therefore, we tested the hypotheses that sodium added to the habitual diet of young adults would reduce flow mediated dilation (FMD) and post-ischemic reactive hyperemia (RH) and that an acute infusion of the antioxidant ascorbic acid (AA) would attenuate the vascular consequences of excess sodium. Methods: Young adults (6M / 8F; age: 26 ± 4 y; BMI: 23.6 ± 2.5 kg/m2) were studied following 10 days of sodium loading (SL) via table salt-filled capsules (3900 mg sodium/day) and 10 days of placebo capsules in addition to their normal diet, in random order. Total sodium intake was estimated via 24-hour urinary sodium content on day 10. On day 11, brachial artery diameter and blood velocity were continuously measured via duplex ultrasound at baseline and after 5 min of forearm ischemia. FMD, the post-ischemic change in brachial artery diameter relative to baseline diameter, provided an index of conduit artery endothelial function. The total RH in the 2 min following ischemia was measured for an index of microvascular function. Within each condition, testing was performed before (pre-AA) and after (post-AA) a 20 min intravenous infusion of 0.06 g of AA/kg lean body mass. Results: Urinary sodium content was increased by SL compared to the placebo (285 ± 94 vs. 160 ± 75 mmol/24 h, p<0.001) indicating approximate sodium intakes of 6600 and 3700 mg/day, respectively. Mean arterial pressure did not differ across conditions pre-AA (SL: 77 ± 7; placebo: 75 ± 5 mmHg, P=0.40) or post-AA (SL: 79 ± 8; placebo: 76 ± 5 mmHg, P=0.17). Brachial artery FMD was not different across time or condition (SL pre-AA: 8.7 ± 3.6, post-AA: 8.8 ± 4.2% vs. placebo pre-AA: 8.8 ± 3.2, post-AA: 8.1 ± 3.5%, time x condition interaction P=0.48). RH was similar following SL and placebo (condition effect: P=0.38) but was reduced in both conditions post AA (SL: Δ-45 ± 44 ml, P=0.01; placebo: Δ-72 ± 59ml, p<0.001). Conclusion: Contrary to our hypothesis, 10 days of sodium loading did not decrease FMD or post- ischemic RH in young adults compared to their habitual diet. Likewise, acute antioxidant treatment did not augment FMD in either condition and paradoxically decreased total RH independent of sodium intake. These data suggest that a short-term increase in dietary sodium intake in healthy young adults does not elicit oxidative stress-induced reductions in vascular function. NIH 5R01HL104106 and 5P20GM113125; AHA 20POST35080171. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Reduction of aerobic metabolism and increased microvascular perfusion during pressure-adjusted static compression as underlying mechanism with potential of preventing chemotherapy-induced neuropathy

Abstract Chemotherapy (CTX)-induced neuropathy [CIPN] limits the maximal applicable dose. Static compression for prevention of CIPN is recommended by guidelines. The postulated underlying effect of reduced microvascular perfusion (MP), however, contradicts current knowledge of elegant in vivo studies. We, thus tested the hypothesis of increased MP combined with reduction of aerobic metabolism in response to pressure-adjusted static compression (PSC) in CTX-induced endothelial damage (CIED). Metabolic oxygen demand (dh), tissue oxygenation (StO2), oxygen supply (O2h) and microvascular perfusion (th) were measured with quantitative time-resolved near infra-red spectroscopy (NIRS) and temperature with thermography on upper extremities following standard procedures in healthy volunteers (n=12, 6 female; age 22±2), peripheral arterial disease patients (n=17, PAD; 75% male, age 68±9 years, 42%, positive controls) and CTX (n=22) with and without clinical CIPN (n=11 each, 46% male; age 64±11 years). Endothelial microvascular function was quantified during post-ischaemic reactive hyperaemia (PIRH). Resting muscle metabolism was quantified by dh during minute 1 of arterial occlusion. Perfusion was quantified by th during venous occlusion. PSC was applied with commercially available compression products and patented palmar pads for up to 90 minutes under standardised and controlled conditions. PSC induces instant and constant fall of temperature (−4.8±0.8°C, p<0.05) and oxygen demand (−3.4±5.2μM, p<0.05). PSC lead to further reduction of tissue metabolism (O2h: −27±38%, dh: −27±38.2%, PIRH-AUC: −20±27%, p<0,05 each compared to without PSC). Oxygen supply increased time-dependently (O2h: 3.0±1.3 μM, p<0.001) as consequence of locally increased perfusion (19±45%, p<0.05) with subsequent rise of tissue oxygenation (StO2: 9.1±4.2, p<0.01) that continued beyond the PSC-duration, indicating a rather metabolic mechanism. This effect is accompanied by a significant similar, albeit lesser reaction on the control hand (p<0.05). PIRH was reduced in controls in response to PSC as a sign for reduced metabolism. In PAD, reaction to PSC was less pronounced and non-significant, reflecting effects of endothelial dysfunction. Patients with CTX with CIPN showed significant endothelial dysfunction compared to controls (StO2 downslope −7±2%, T95 (s) 13±5, PIRH-AUC 9±6, p<0.05 each) and to CTX without CIPN (p<0.05 each), like PAD. For the first time, CIED as result of CTX comparable to atherosclerotic disease is shown. In contrast to previous assumptions of clinicians propagating compression therapy for prevention of CIPN, the results presented prove that not constriction of the products, but rather a combination of increased local perfusion and oxygen delivery in combination with mechanical effects on the low pressure system and reduced metabolism is induced by PSC. These findings open the field for well-designed RCTs to develop novel treatment options for CIPN targeting CIED. Funding Acknowledgement Type of funding sources: Private company. Main funding source(s): MEDIACC GmbH

Pravastatin improves postprandial endothelial dysfunction and hemorheological deterioration in patients with effort angina pectoris.

Postprandial hypertriglyceridemia and hyperglycemia may promote endothelial and hemorheological dysfunction. The present study investigated the effects of pravastatin on endothelial function and hemorheology in patients with stable angina pectoris (AP) before and after eating a test meal. We recruited 26 patients with stable AP who had impaired glucose tolerance and mild dyslipidemia and six healthy men as controls to assess endothelial function and hemorheological behavior. In each group, we measured forearm blood flow (FBF) during post-ischemic reactive hyperemia and obtained blood samples before and 2h after the test meal. Pravastatin 20mg/day was then commenced in the 26 AP patients. The above tests were repeated after 2 days and 6 months. Maximum FBF during hyperemia in the baseline fasting phase was significantly lower in the AP patients than in the controls (p < 0.05). Fasting and postprandial FBF during reactive hyperemia time-dependently improved after pravastatin treatment (p < 0.05 vs. baseline data for each phase). Pravastatin treatment for 6 months, but not for 2 days, inhibited leukocyte activation and improved hemorheological parameters. In conclusion, pravastatin treatment for 6 months improved fasting and postprandial endothelial and hemorheological dysfunction in AP patients.

Abstract 109: Association of Endothelial Dysfunction with Non-invasive Measures of Vascular Stiffness in Young-middle Aged Non-hypertensive Individuals

Arterial stiffness and enhanced wave reflections independently predict cardiovascular risk. Wave reflections augment central (aortic) pulse pressure (PP), an index of arterial stiffness, and systolic pressure. Increased wave reflections and PP have previously been associated with endothelial dysfunction in hypertensive and healthy middle-aged adults. The study objective was to determine whether endothelial dysfunction is associated with PP and other measures of vascular stiffness in young normotensive and prehypertensive subjects. We measured office, central, and 24-hour measurements in 102 (64 female, 38 male) non-hypertensive, non-diabetic participants. Endothelial function was assessed non-invasively using post-ischemic reactive hyperemia with strain-gauge plethysmography. The racially diverse subject pool was comprised of 60% Caucasians, 18% African Americans, and 24% Asians, with mean age 30, mean BMI 25.6, mean office SBP/DBP = 110 ± 13 mm Hg/70 ± 9 mm Hg. Endothelial function was highly associated with office (β= - 4.2 mm Hg, p&lt;0.001) and 24-hour PP (β= - 1.4 mm Hg, p=0.008), along with central measures of wave reflection: ((augmentation pressure (β= - 2.1 mm Hg), augmentation index (β= - 3.7): both p&lt;0.001). Beta values correspond to the change noted for one standard deviation in endothelial function. In conclusion, endothelial dysfunction is significantly and consistently associated with arterial stiffness and increased wave reflections in young non-hypertensive adults. Identification of endothelial dysfunction in otherwise healthy young individuals may provide an opportunity to reduce vascular stiffness and associated cardiovascular risk.

The vascular response to vasodilators is related to the membrane content of polyunsaturated fatty acids in hypertensive patients.

Abnormal vascular reactivity contributes to the pathophysiology of hypertension and hypertension-related organ damage. As the dietary content of fatty acids may affect the vascular responses, we investigated the relationship of endothelium-independent and endothelium-dependent vasodilation with the fatty acid composition of red blood cell (RBC) membranes in hypertension. In 45 uncomplicated hypertensive patients, we measured the content of fatty acids in RBC membrane as a marker of dietary intake of fatty acids, and the vasodilatory response of the brachial artery to both nitrate-donor compound (nitrate-mediated vasodilation, NMD) and postischemic reactive hyperemia (flow-mediated vasodilation, FMD). Baseline diameter of the brachial artery was significantly lower and vasodilatory response to NMD was significantly greater in patients with RBC membrane polyunsaturated-to-saturated fatty acid (PUFA/SFA) ratio above the median of the distribution than in patients with PUFA/SFA ratio below the median, whereas no difference was observed in FMD. n-3 PUFA and n-6 PUFA content, and the PUFA/SFA ratio of RBC membranes were related inversely with brachial artery diameter and directly with maximal NMD, whereas no relationship of fatty acid components of RBC membrane with FMD was observed. Multivariate analysis that included demographic, anthropometric, clinical, and biochemical variables indicated that the RBC membrane PUFA/SFA ratio was an independent determinant of brachial artery diameter and NMD response. The endothelium-independent brachial artery vasodilation is independently related to the PUFA content of RBC membranes in patients with hypertension. This suggests the possible benefits of PUFA-enriched diets on the regulation of vascular tone and blood pressure in these patients.

Microvascular reactivity in women with gestational diabetes mellitus studied during pregnancy.

AimTo compare microvascular reactivity assessed in the skin using laser Doppler fluximetry (LDF) in women with gestational diabetes mellitus (GDM) and gestational age-matched control during pregnancy.Methods110 pregnant women at ~33 weeks gestation participated in the study. Skin microvascular reactivity was evaluated by LDF, at rest, during the response to brief arterial occlusion (post occlusive hyperaemic response) and during sympathetically mediated vasoconstrictor response to deep inspiratory breath hold.ResultsNo statistically significant differences were found in the microvascular variables studied (resting and maximum rate flux, post-ischaemic reactive hyperaemia and deep inspiratory breath holds) between +GDM and –GDM groups women. In women with GDM there was a negative correlation between resting flux and the response to the oral glucose tolerance test (OGTT), r = -0.282 (p = 0.037). There was also a negative correlation between the response to the OGTT and the sympathetically mediated constrictor response to inspiratory breath holds (r = -.298, p = .030) but not in women with GDM (r = .102, r = .468).ConclusionAttenuated microvascular reactivity as an early marker of endothelial dysfunction is not present in women with GDM when assessed during pregnancy.

Influence of Cardiac Decentralization on Cardioprotection

The role of cardiac nerves on development of myocardial tissue injury after acute coronary occlusion remains controversial. We investigated whether acute cardiac decentralization (surgical) modulates coronary flow reserve and myocardial protection in preconditioned dogs subject to ischemia-reperfusion. Experiments were conducted on four groups of anesthetised, open-chest dogs (n = 32): 1- controls (CTR, intact cardiac nerves), 2- ischemic preconditioning (PC; 4 cycles of 5-min IR), 3- cardiac decentralization (CD) and 4- CD+PC; all dogs underwent 60-min coronary occlusion and 180-min reperfusion. Coronary blood flow and reactive hyperemic responses were assessed using a blood volume flow probe. Infarct size (tetrazolium staining) was related to anatomic area at risk and coronary collateral blood flow (microspheres) in the anatomic area at risk. Post-ischemic reactive hyperemia and repayment-to-debt ratio responses were significantly reduced for all experimental groups; however, arterial perfusion pressure was not affected. Infarct size was reduced in CD dogs (18.6±4.3; p = 0.001, data are mean±1SD) compared to 25.2±5.5% in CTR dogs and was less in PC dogs as expected (13.5±3.2 vs. 25.2±5.5%; p = 0.001); after acute CD, PC protection was conserved (11.6±3.4 vs. 18.6±4.3%; p = 0.02). In conclusion, our findings provide strong evidence that myocardial protection against ischemic injury can be preserved independent of extrinsic cardiac nerve inputs.

Polycystic ovary syndrome has no independent effect on vascular, inflammatory or thrombotic markers when matched for obesity

SummaryIntroduction Previous studies investigating cardiovascular (CV) risk in obese women with polycystic ovary syndrome (PCOS) have been potentially confounded by not adequately accounting for body weight. Objective To assess if PCOS increases CV risk independently in young obese women by examining carotid intima-media wall thickness (cIMT) and platelet function. Design A case–control study comparing women with PCOS (n = 21) to age (32·8 ± 7·2 vs 33·5 ± 6·7 years), and weight (100·9 ± 16·7 vs 99·3 ± 14·7 kg)-matched controls (n = 19). Platelet function was examined by flow cytometry, clot structure and fibrinolysis by turbidimetric assays and endothelial function by ELISA and post ischaemic reactive hyperaemia. Results The PCOS group had higher testosterone 1·2 ± 0·3 vs 0·9 ± 0·3 nmol/l (P = 0·01), HOMA-IR 2·5 ± 1·7 vs 1·7 ± 1·0 (P = 0·08), impaired glucose regulation 33·3% vs 5·3% (P = 0·02), and urinary isoprostane 16·0 ± 4·4 vs 11·8 ± 7·1 ng/ml (P = 0·04) compared to controls. Mean cIMT 0·5 ± 0·05 vs 0·48 ± 0·06 mm (P = 0·36), and basal platelet surface expression (percentage of positive cells) of P-selectin 0·52 ± 0·3 vs 0·43 ± 0·23 (P = 0·40) and fibrinogen binding 0·97 ± 0·4 vs 0·83 ± 0·3 (P = 0·48) did not significantly differ between the PCOS and control groups respectively. Furthermore, platelets sensitivity to stimulation with adenosine-5′-diphosphate or inhibition with prostacyclin, clot structure and fibrinolytic efficiency ex vivo, endothelial reactive hyperaemic index (RHI), inflammation (hsCRP) and adhesion markers (sE-selectin, sP-selectin, sVCAM-1 and sICAM-1) were not significantly different between the two groups. Conclusions PCOS appeared not to independently increase atherothrombotic risk when matched for obesity. It is likely that any excess CV risk in young obese women with PCOS can either be attributed to obesity or is not yet apparent at this early stage of the condition.

Reduced six-minute walking distance, high fat-free-mass index and hypercapnia are associated with endothelial dysfunction in COPD

This study investigated the determinants of endothelial function in patients with chronic obstructive pulmonary disease (COPD). Digital pulse amplitude augmentation was measured by post-ischemic reactive hyperemia (RH-PAT) in 44 COPD patients and analyzed with covariates: condition vs. exacerbation, fat-free mass index (FFMI), pulmonary function, blood pressure, inflammation, six-minute walking distance, muscle function, medications, diabetes and prevalent cardiovascular diseases. RH-PAT was 0.43 (-0.14 to 1.30) with 50% of patients exhibiting abnormal RH-PAT ≤ 0.40. After adjustment for age and sex, RH-PAT was linked to condition, FFMI, myocardial infarction history, FEV(1), PaCO(2), heart rate, bicarbonates, inflammation and walking distance (p<0.10). In multivariate analysis, walking distance, FFMI and PaCO(2) were independent contributors of RH-PAT explaining 49% of the variance (p<0.0001). Higher FFMI was associated with higher inflammation, oxidative stress and endothelial dysfunction. Six-minute walking distance which is a widely available marker of severity and functional capacity in COPD patients is a main predictor of endothelial dysfunction.

Inflammatory biomarkers are unrelated to endothelial-mediated vasodilation in physically active young men

Aron A, Hargens TA, Guill SG, Herbert WG. Inflammatory biomarkers are unrelated to endothelial-mediated vasodilation in physically active young men. J. Hum. Sport Exerc. Vol. 7, No. 2, pp. 581-588, 2012. Endothelial dysfunction has an important role in genesis of atherosclerosis and is depicted by a series of inflammatory and endothelial biomarkers. Shear stress arising from repeated episodes of increased blood flow with physical activity (PA) is a possible mechanism that improves vascular endothelial function. Our purpose was to examine whether inflammatory markers mediate the association between PA and endothelial function. Subjects were young, healthy men recruited according to recreational PA habits: highactive (n=21) vs. sedentary (n=17). Active subjects reported >45 min/day of moderate-vigorous physical activities, >4 days/week over 6 months, while sedentary subjects reported no recreational physical activity. Fasting serum samples were analyzed for C-reactive protein (CRP), tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6). Endothelial function was determined using flow-mediated dilation of the brachial artery induced by post ischemic reactive hyperemia. Hyperemia response was greater in the high-active than in sedentary men (30.2±8.2 vs. 24.3±5.2 mL/min/100mL; P<0.001). There were no differences between the groups with respect to CRP, TNF-α, or IL-6. Concentrations of these inflammatory biomarkers were unrelated to reactive hyperemia differences attributable to PA. Improved hyperemic response seen in young physically active subjects may be influenced by factors beyond the inflammatory factors, e.g., enhanced nitric oxide production. Physical activity was associated with an increased vascular function in young adults, although a diminished inflammatory state was no revealed. Additional research is needed to clarify the role of PA on cytokine indicators of inflammation and how this relates to endothelial function. Key

Apyrase treatment of myocardial infarction according to a clinically applicable protocol fails to reduce myocardial injury in a porcine model

BackgroundEctonucleotidase dependent adenosine generation has been implicated in preconditioning related cardioprotection against ischemia-reperfusion injury, and treatment with a soluble ectonucleotidase has been shown to reduce myocardial infarct size (IS) when applied prior to induction of ischemia. However, ectonucleotidase treatment according to a clinically applicable protocol, with administration only after induction of ischemia, has not previously been evaluated. We therefore investigated if treatment with the ectonucleotidase apyrase, according to a clinically applicable protocol, would reduce IS and microvascular obstruction (MO) in a large animal model.MethodsA percutaneous coronary intervention balloon was inflated in the left anterior descending artery for 40 min, in 16 anesthetized pigs (40-50 kg). The pigs were randomized to 40 min of 1 ml/min intracoronary infusion of apyrase (10 U/ml, n = 8) or saline (0.9 mg/ml, n = 8), twenty minutes after balloon inflation. Area at risk (AAR) was evaluated by ex vivo SPECT. IS and MO were evaluated by ex vivo MRI.ResultsNo differences were observed between the apyrase group and saline group with respect to IS/AAR (75.7 ± 4.2% vs 69.4 ± 5.0%, p = NS) or MO (10.7 ± 4.8% vs 11.4 ± 4.8%, p = NS), but apyrase prolonged the post-ischemic reactive hyperemia.ConclusionApyrase treatment according to a clinically applicable protocol, with administration of apyrase after induction of ischemia, does not reduce myocardial infarct size or microvascular obstruction.

Acute and Subacute Effect of Rheopheresis on Microvascular Endothelial Function in Patients Suffering From Age‐related Macular Degeneration

This study was performed on seven patients affected by the atrophic form of age-related macular degeneration (AF-ARMD). The patients under investigation belonged to a larger study aimed at evaluating the efficacy of rheopheresis treatment (RT) on the visual function of AF-ARMD patients. Following the protocol of the larger study, patients received RT twice a week, every two weeks, for a total of ten treatments, as well as high-dose supplementation with zinc and vitamins A, E and beta-carotene. Recruited patients underwent skin laser Doppler flowmetry coupled with skin iontophoresis of the endothelium-dependent vasodilator acetylcholine (ACh) and a test of skin post-ischemic reactive hyperemia, before and after the first RT (time 1: all seven patients) and the fifth RT (time 2: six patients). A significantly higher absolute (anova for repeated measures) and relative (percentage change from the baseline) skin blood flux response (SBFR) to ACh iontophoresis was observed after RT, compared to before RT at time 1 (679 +/- 43% and 436 +/- 78%, respectively; P < 0.05), as well as before RT at time 2 compared to before RT at time 1 (683 +/- 74% and 436 +/- 78%, respectively; P < 0.05). Absolute and relative SBFR to ischemia did not differ either after RT compared to before RT at time 1, or before RT at time 2 compared to before RT at time 1. These findings are consistent with an acute and subacute beneficial effect of RT on skin microvascular endothelial function in the studied AF-ARMD patients.

Haptoglobin genotype and endothelial function in diabetes mellitus: a pilot study

Endothelial function (EnF) is impaired in patients with diabetes mellitus (DM) due in large part to an increase in oxidative stress. Haptoglobin (Hp) is a potent antioxidant protein which is encoded by two different alleles (1 and 2) with the Hp 1 protein being a superior antioxidant to the Hp 2 protein. We hypothesized that DM individuals with the Hp 2-2 genotype would have greater endothelial dysfunction as compared to DM individuals with the Hp 1-1 genotype. We studied EnF in 16 Hp 2-2, 14 Hp 1-1 DM individuals and 14 healthy subjects. DM patients' groups were matched in terms of age, cardiovascular risk factors and metabolic characteristics. EnF was assessed using post-ischemic reactive hyperemia and strain gauge plethysmography and expressed either as the maximal flow after the ischemic period or as the area under the flow-time curve (AUC). We showed that EnF indices, AUC and maximal flow, were also higher in the healthy and Hp 1-1 groups compared with Hp 2-2 genotype group (615 +/- 60 and 600 +/- 40 vs. 450 +/- 50 ml dl(-1), 29 +/- 2.6 and 25 +/- 3 vs. 14 +/- 1.8 ml min(-1) dl(-1), P < 0.003 and P < 0.05, for AUC and maximal flow, one-way ANOVA, respectively). We concluded that Hp 2-2 diabetic patients had a worse EnF than controls and Hp 1-1 diabetic subjects.

Effects of Pitavastatin on Fasting and Postprandial Endothelial Function and Blood Rheology in Patients With Stable Coronary Artery Disease

Because postprandial hypertriglyceridemia and hyperglycemia may promote atherosclerosis, the present study investigated the effects of a clinical dose of pitavastatin on endothelial function and blood rheology in patients with coronary artery disease (CAD) before and after eating a test meal. The 16 patients with stable CAD and mild dyslipidemia and 6 age-matched healthy men as controls were recruited. In each group, forearm blood flow (FBF) was measured during postischemic reactive hyperemia and blood samples were taken before and 2 h after the test meal. Urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) was also measured. The patients were started on pitavastatin 2 mg/day. The tests were repeated after 6 months. Maximum FBF during hyperemia in the baseline fasting phase was significantly lower in CAD patients than in control subjects (P=0.040). Fasting and postprandial FBF during reactive hyperemia significantly improved after pitavastatin treatment (P<0.05 vs baseline data for each phase) associated with reduced urine 8-OHdG, increased plasma adiponectin and improved lipid profile. No significant differences in baseline rheological parameters were seen between controls and CAD patients. Pitavastatin significantly improved fasting and postprandial dyslipidemia and endothelial dysfunction in CAD patients, partly via reducing oxidative stress and increasing plasma adiponectin, although rheological parameters remained unchanged.

Reliability of Lightguide Spectrophotometry (O2C®) for the Investigation of Skin Tissue Microvascular Blood Flow and Tissue Oxygen Supply in Diabetic and Nondiabetic Subjects

Skin microvascular assessment has progressed to an important evaluation in patients with diabetes mellitus. This study was done to evaluate a new device using micro-lightguide spectrophotometry in the assessment of skin microvascular function. Twenty nondiabetic subjects (age 46.6 +/- 14.8 years; mean +/- SD) and 20 diabetic patients (age 59.4 +/- 8.4 years) participated in repeated microvascular measurements using micro-lightguide spectrophotometry. This technique allows simultaneous, noninvasive measurement of microvascular blood flow and hemoglobin oxygenation (SO(2)) at the same anatomical area in different tissue layers. A skin probe was placed on nonhairy skin at the thenar eminence of the left hand for the measurement of SO(2), and the postischemic reactive hyperemia response (PRH) was measured in skin and underlying muscle tissue. Repeated measurements in PRH revealed a good correlation at the superficial skin layer (r = 0.97, p < 0.0001) with a coefficient of variation at 9.2 +/- 1.7% and at the superficial muscle layer (r = 0.80, p < 0.0002) with a coefficient of variation at 9.7 +/- 1.5%. A slightly weaker correlation was observed for the SO(2) measurement at the skin layer (r = 0.69 +/- p < 0.0001) with a coefficient of variation at 17.5 +/- 3.8% and at the muscle layer (r = 0.48; p = 0.0016) with a coefficient of variation at 18.1 +/- 10.5%. Lightguide spectrophotometry is an easy, noninvasive, and reliable method for simultaneous measurement of superficial microvascular blood flow by laser Doppler fluxmetry and skin oxygenation by spectrophotometry. Further studies are required to clarify the validity of these measures in special patient populations such as diabetes mellitus with specified microvascular complications.

Post-ischaemic peak flow and myogenic flowmotion component are independent variables for skin post-ischaemic reactive hyperaemia in healthy subjects

The aim of this study was to clarify whether the post-ischaemic amplification of skin blood flowmotion (SBF) influences the extent of skin post-ischaemic hyperaemia. Forearm skin perfusion was measured by means of laser Doppler flowmetry (LDF) and forearm SBF was examined using Fourier analysis of LDF signal, under basal conditions and following forearm ischaemia in 50 healthy subjects. Power spectral density (PSD) of SBF total spectrum (0.009-1.6 Hz), as well of the frequency intervals (FI) related to endothelial (0.009-0.02 Hz), sympathetic (0.02-0.06 Hz), myogenic (0.06-0.2 Hz), respiratory (0.2-0.6 Hz) and cardiac (0.6-1.6 Hz) activity was measured in PU(2) (LDF perfusion unit)/Hz. Multiple regression analysis evaluated whether post-ischaemic peak-flow, as an indicator of shear stress, or post-ischaemic SBF independently affected the post-peak-flow hyperaemia calculated as corrected area under the LDF curve (C-AUC). Following ischaemia, we observed a statically significant increase in skin perfusion (from basal of 11.7+/-5.8 PU to peak flow of 62.3+/-41.4 PU, p<0.0000005) and in PSD of SBF total spectrum (p<0.01) as well of the different FI considered (p<0.005 for the endothelial and myogenic FI; p<0.05 for the sympathetic, respiratory and cardiac FI) compared to baseline. Multiple regression analysis showed that peak flow and post-ischaemic SBF component of myogenic origin were significant independent variables for the C-AUC (p=0.0000001 and p=0.009, respectively). These findings suggest that not only increased shear stress but also post-ischaemic amplification of myogenic SBF component independently contributes to the more prolonged phase of post-ischaemic skin re-perfusion in healthy subjects.

The ADP receptor P2Y1 mediates t-PA release in pigs during cardiac ischemia

The endothelial ADP receptor P2Y(1) is responsible for a large part of the reactive hyperemia following cardiac ischemia. Tissue plasminogen activator (t-PA) increases during reactive hyperemia. We postulated that the release of t-PA during reactive hyperemia could be mitigated through blocking the coronary endothelial P2Y(1) receptor. t-PA was measured in peripheral arterial blood and locally in the venous blood from the coronary sinus in a porcine model. The stable ADP analogue 2-MeSADP (10(-5) M), alone or as co-infusion with a selective P2Y(1) receptor blocker, MRS2179 (10(-3) M) was locally delivered in the left anterior descending artery through the tip of a coronary angioplasty balloon. In separate pigs the coronary artery was occluded with the balloon for 10 min. During the first and tenth minute of coronary ischemia, 2.5 ml of MRS2179 (10(-3) M) was delivered distal to the occlusion in 8 pigs, 10 pigs were used as controls. 2-MeSADP increased levels of t-PA in the coronary sinus, which could be significantly inhibited by co-infusion with MRS2179. During cardiac ischemia and reperfusion, t-PA increased significantly, an effect that could be significantly inhibited by MRS2179. Intra coronary administered MRS2179, a selective P2Y(1) receptor blocker, significantly reduces the increased levels of t-PA caused by both 2-MeSADP and cardiac ischemia in coronary arteries. Thus, ADP acting on the endothelial P2Y(1) receptor may mediate release of t-PA during ischemia and post-ischemic hyperemia, an effect that may counteract some of the platelet activating effects of ADP. Abbreviated Abstract We postulated that the release of t-PA during post ischemic reactive hyperemia could be mitigated through blocking the coronary endothelial P2Y(1) receptor in a porcine model. The ADP analogue 2-MeSADP (10(-5) M), alone or as co-infusion with a the P2Y(1) receptor blocker, MRS2179 (10(-3) M) was locally delivered in the left anterior descending artery. In separate pigs the coronary artery was occluded for ten min. During the first and tenth min of coronary ischemia, 2.5 ml of MRS2179 (10(-3) M) was delivered distal to the occlusion. t-PA was measured in peripheral arterial blood and also from the Coronary Sinus. We found that levels of t-PA in the blood from the coronary Sinus increased during infusion with 2-MeSADP as well as during ischemia and reperfusion. In pigs treated with MRS2179 levels of t-PA in the Coronary Sinus were significantly reduced during both coinfusion with 2-MeSADP and during ischemia/reperfusion. Thus, ADP acting on the endothelial P2Y(1) M receptor may mediate release of t-PA during ischemia and post-ischemic hyperemia, an effect that may counteract some of the platelet activating effects of ADP.

Blood Oxygenation Level–Dependent Magnetic Resonance Imaging of the Skeletal Muscle in Patients With Peripheral Arterial Occlusive Disease

Blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI) has been used to measure T2* changes in skeletal muscle tissue of healthy volunteers. The BOLD effect is assumed to primarily reflect changes in blood oxygenation at the tissue level. We compared the calf muscle BOLD response of patients with peripheral arterial occlusive disease (PAOD) to that of an age-matched non-PAOD group during postischemic reactive hyperemia. PAOD patients (n=17) with symptoms of intermittent calf claudication and an age-matched non-PAOD group (n=11) underwent T2*-weighted single-shot multiecho planar imaging on a whole-body magnetic resonance scanner at 1.5 T. Muscle BOLD MRI of the calf was performed during reactive hyperemia provoked by a cuff-compression paradigm. T2* maps were generated with an automated fitting procedure. Maximal T2* change (deltaT2*(max)) and time to peak to reach deltaT2*(max) for gastrocnemius, soleus, tibial anterior, and peroneal muscle were evaluated. Compared with the non-PAOD group, patients revealed significantly lower deltaT2*(max)-values, with a mean of 7.3+/-5.3% versus 13.1+/-5.6% (P<0.001), and significantly delayed time-to-peak values, with a mean of 109.3+/-79.3 versus 32.2+/-13.3 seconds (P<0.001). T2* time courses of the muscle BOLD MRI signal during postocclusive reactive hyperemia revealed statistically significant differences in the key parameters (deltaT2*(max); time to peak) in PAOD patients compared with age-matched non-PAOD controls.

Forelimb postischaemic reactive hyperaemia is impaired by hypotensive low body negative pressure in healthy subjects

Local metabolic conditions adapt blood supply to metabolic requirement by a direct effect on vascular smooth muscles and indirectly by modulating sympathetic vasoconstrictor effectiveness. During exercise, sympathetic nervous activity could in turn interfere on local metabolic control of vascular tone and restrain blood flow to active muscles. In order to investigate that interaction non-invasively, we measured postischaemic reactive hyperaemia (RH) in the forelimb of eight healthy young men (22.7 +/- 2.1 years) at rest and during two levels of sympathetic stimulation using low body negative pressure (LBNP -15 and -30 mmHg). During every stages, RH was measured after 40, 60, 90 and 180 s of arterial occlusion, respectively. In control conditions, RH rose with duration of ischaemia (18.9, 24.2, 30.4, 33.1 ml min(-1) per 100 ml(-1) for 40, 60, 90 and 180 s of ischaemia, respectively). During non-hypotensive LBNP (-15 mmHg) sympathetic activation was associated with decreased forelimb blood flow (6.4 +/- 0.9 versus 3.9 +/- 0.6 ml min(-1) per 100 ml(-1), P<0.01), but RH were not significantly different from control conditions. During hypotensive tachycardia LBNP (-30 mmHg), RH were significantly lower than under the previous LBNP stage. This fall in RH was greater after the shortest gap of ischaemia and tapered off as arterial occlusion gap increased (-22.3, -13.1, -10.5 and -8.7% for 40, 60, 90 and 180 s of ischaemia, respectively). These results suggested that vascular tone adaptation to local metabolic conditions was modified by sympathetic nervous activation. This was particularly marked when an hypotensive-mediated sympathetic stimulation was opposed to short gaps of ischaemia.

Influence of vascular filling and perfusion on BOLD contrast during reactive hyperemia in human skeletal muscle

Mechanisms generating BOLD contrast are complex and depend on parameters that are prone to large variations, in particular in skeletal muscle. Here, we simultaneously measured perfusion by ASL, and BOLD response in the calf muscle of 6 healthy volunteers during post-ischemic reactive hyperemia. We tested whether the relation between the two was altered for varying degrees of leg vascular replenishment induced by prior positioning of the leg at different heights relative to the heart. We found that the BOLD response depended on perfusion, but also on the degree of repletion of leg blood vessels. We conclude that simultaneous determination of perfusion by ASL is important to identify the mechanisms underlying BOLD contrast in the skeletal muscle.