Early Microvascular Dysfunction Research Articles

Early Retinal Arteriolar Changes and Peripheral Neuropathy in Diabetes

OBJECTIVETo examine the association between early retinal arteriolar abnormalities and diabetic peripheral neuropathy (DPN).RESEARCH DESIGN AND METHODSData from 608 people (aged 40–80 years) with diabetes from the population-based Singapore Malay Eye Study were analyzed. Participants underwent binocular two-field digital retinal photography and quantitative sensory testing. DPN was defined as an abnormal response to a monofilament or neurothesiometer test. Quantitative changes of retinal vascular caliber and arteriolar bifurcation geometry were measured using a computer-based program. Qualitative retinal signs of retinopathy and retinal arteriolar wall signs were graded by standardized methods.RESULTSDPN was present in 155 people (25.5%). After adjusting for age, sex, diabetes duration, HbA1c, cardiovascular risk factors, antihypertensive medication use, and peripheral arterial disease, people with suboptimal arteriolar caliber (odds ratio 1.94 [95% CI 1.22–3.10]), larger arteriolar branching coefficient (1.58 [1.03–2.42]), diabetic retinopathy (1.82 [1.20–2.75]), and focal arteriolar narrowing (2.92 [1.48–5.76]) were more likely to have DPN. Participants with a greater number of retinal microvascular signs were more likely to have DPN than those without retinal changes (6.11 [2.11–17.71] for two or more signs and 3.47 [1.18–10.21] for one sign compared with none).CONCLUSIONSIndividuals with diabetes with early retinal arteriolar abnormalities are more likely to have DPN, independent of hyperglycemia and major vascular risk factors. These data support the hypothesis that early microvascular dysfunction, evident in the retina, is an independent risk factor for DPN.

Relation of Impaired Coronary Microcirculation to Increased Urine Albumin Excretion in Patients With Systemic Hypertension and No Epicardial Coronary Arterial Narrowing

Coronary flow reserve (CFR) is impaired and urinary albumin excretion is increased in patients with essential hypertension. Our aim was to investigate the associations between CFR and cardiac and renal damage in hypertensives. For this purpose we studied 37 never-treated hypertensives (57.9 years old, 16 men) without chest pain but with a positive ischemia stress test result and normal coronary arteries on coronary angiogram. CFR was calculated by a 0.014-inch Doppler guidewire (Flowire, Volcano, San Diego) in the left anterior descending artery in response to bolus intracoronary administration of adenosine (60 μg) as the ratio of hyperemic to basal average peak velocity of the distal vessel. All participants underwent complete echocardiographic study including left ventricular diastolic function evaluation by tissue Doppler imaging (peak early diastolic velocity/peak atrial systolic velocity) and determination of the albumin-to-creatinine ratio (ACR). Hypertensives with low CFR (<2.5, n = 22) compared to those with high CFR (n = 15) exhibited a larger left ventricular mass index by 10.9 g/m(2) (p = 0.045) and ACR values by 10 mg/g (p <0.001). CFR was negatively correlated with logACR (r = -0.511, p = 0.001). LogACR (beta -0.792, p <0.001), male gender (beta 0.313, p = 0.005), left ventricular mass index (beta -0.329, p = 0.007), and peak early diastolic velocity/peak atrial systolic velocity (beta 0.443, p <0.001) were the only independent predictors of CFR in linear regression analysis (adjusted R(2) = 0.672). In conclusion, never-treated asymptomatic hypertensives who exhibit impaired CFR and angiographically normal epicardial arteries are characterized by intrarenal vascular damage as reflected by increased ACR. These findings suggest a plausible role of ACR estimation in the identification of hypertensive subjects with early coronary microvascular dysfunction.

Compartment syndrome–induced microvascular dysfunction: an experimental rodent model

Acute compartment syndrome (CS) is a limb-threatening disease that results from increased intracompartmental pressure. The pathophysiologic mechanisms by which this occurs are poorly understood. This study was designed to measure the effects of increased intracompartmental pressure on skeletal muscle microcirculation, inflammation and cellular injury using intravital videomicroscopy (IVVM) in a clinically relevant small animal model. We induced CS in 10 male Wistar rats (175-250 g), using a saline infusion technique. Intracompartmental pressure was controlled between 30 and 40 mm Hg and maintained for 45 minutes. After fasciotomy, the extensor digitorum longus muscle was visualized using IVVM, and perfusion was quantified. We quantified leukocyte recruitment to measure the inflammatory response. We measured muscle cellular injury using a differential fluorescent staining technique. The number of nonperfused capillaries increased from 12.7 (standard error of the mean [SEM] 1.4 ) per mm in the control group to 30.0 (SEM 6.7) per mm following 45 minutes of elevated intracompartmental pressure (CS group; p = 0.031). The mean number of continuously perfused capillaries (and SEM) decreased from 78.4 (3.2) per mm in the control group to 41.4 (6.9) per mm in the CS group (p = 0.001). The proportion of injured cells increased from 5.0% (SEM 2.1%) in the control group to 16.3% (SEM 6.8%) in the CS group (p = 0.006). The mean number of activated leukocytes increased from 3.6 (SEM 0.7) per 100 μm(2) in the control group to 8.6 (SEM 1.8) per 100 μm(2) in the CS group (p = 0.033). Early CS-induced microvascular dysfunction resulted in a decrease in nutritive capillary perfusion and an increase in cellular injury and was associated with a severe acute inflammatory component.

Retinal Arteriolar Dilation Predicts Retinopathy in Adolescents With Type 1 Diabetes

OBJECTIVE—Alterations in retinal vascular caliber may reflect early subclinical microvascular dysfunction. In this study, we examined the association of retinal vascular caliber to incident retinopathy in young patients with type 1 diabetes.RESEARCH DESIGN AND METHODS—This was a prospective cohort study of 645 initially retinopathy-free type 1 diabetic patients, aged 12–20 years. Participants had seven-field stereoscopic retinal photographs taken of both eyes at baseline and follow-up. Retinal vascular caliber was measured from baseline photographs using a computer-based program following a standardized protocol. Incident retinopathy was graded according to the modified Airlie House classification from follow-up photographs.RESULTS—Over a median follow-up of 2.5 years, 274 participants developed retinopathy (14.8 per 100 person-years). After adjustments for age, sex, diabetes duration, glycemia, mean arterial blood pressure, BMI, and cholesterol levels, larger retinal arteriolar caliber (fourth versus first quartile) was associated with a more than threefold higher risk of retinopathy (hazard rate ratio 3.44 [95% CI 2.08–5.66]). Each SD increase in retinal arteriolar caliber was associated with a 46% increase in retinopathy risk (1.46 [1.22–1.74]). This association was stronger in female than in male participants. After similar adjustments, retinal venular caliber was not consistently associated with incident retinopathy.CONCLUSIONS—Retinal arteriolar dilatation predicts retinopathy development in young patients with type 1 diabetes. Our data suggest that arteriolar dysfunction may play a critical role in the pathogenesis of early diabetic retinopathy and that computer-based retinal vascular caliber measurements may provide additional prognostic information regarding risk of diabetes microvascular complications.

Early microvascular and macrovascular dysfunction is not accompanied by structural arterial injury in polycystic ovary syndrome

During the last decade cardiovascular risk factors and endothelial dysfunction have been shown to be present early in life in women with Polycystic Ovary Syndrome (PCOS). The aim of the present study was a global assessment of abnormalities in the arterial bed of young women with PCOS by non-invasive, reproducible methods. 27 women with PCOS and 27 control women of comparable age, body mass index and waist-to-hip ratio were studied. Macrovascular function was assessed by flow-mediated dilatation (FMD) on the brachial artery. Nitrate-induced dilatation (NID) was performed to exclude a vascular smooth muscle cells injury. Microvascular function was assessed by venous occlusion plethysmography studying forearm blood flow. Arterial structure was evaluated by ultrasonographic assessment of intima-media thickness (IMT) of the carotid artery. FMD values were lower in women with PCOS compared to controls (PCOS: 3.84+/-0.74% vs. controls: 9.83+/-0.97%, P<0.001), but no difference was observed in NID (PCOS: 16.59+/-1.84% vs. controls: 16.64+/-2.05%, P=0.98) values. The time required for reactive hyperemia to reach peak value, a plethysmography parameter, was longer in PCOS women (PCOS: 20.63+/-4.67 sec vs. controls: 10.38+/-5.11 sec, P=0.02). No difference was observed in the combined IMT among the studied groups (PCOS: 0.49+/-0.01 mm v.s. controls: 0.51+/-0.02 mm, P=0.19). Using non invasive methodologies endothelial dysfunction in the macrocirculation and early impairment in the microcirculation were demonstrated in young women with PCOS who had normal profile of glycemia, lipidemia and blood pressure, and no evidence of structural arterial impairment.

MICROVASCULAR HEMODYNAMICS AND TISSUE pH AFTER HEMORRHAGIC SHOCK RESUSCITATION WITH PEG-ALBUMIN AND HYDROXYETHYL STARCH

The hamster chamber window model was subjected to hemorrhagic shock by the withdrawal of 50% of blood volume (BV). Blood volume was restored one hour after hemorrhage with a single volume infusion (resuscitation) of 25% BV with polyethylene glycol conjugated bovine serum albumin (PEG-Alb) and hydroxyethyl starch (HES). Hemorrhage, shock and resuscitation were monitored continuously in terms of mean arterial pressure (MAP), laboratory parameters, microvascular blood flow, capillary perfusion, tissue pH and intravascular and tissue pO2. Microvascular oxygen delivery and extraction were calculated and corrected for pH effect on hemoglobin saturation. Resuscitation with PEG-Alb restored and sustained systemic and microvascular parameters up to the end of the observation period (90 min). HES was identical to PEG-Alb resuscitation during the initial 15 min but was not sustained subsequently. The trend of recovery in MAP for HES persisted beyond the time when both capillary perfusion and tissue pH decreased. Thus, MAP was not indicative of early microvascular dysfunction. Early differences found at the microvascular levels suggest that data based decisions regarding resuscitation may be short and on the order of minutes. Furthermore, PEG-Alb appears to provide both early and long term sustained systemic and microvascular recovery when used to restitute perfusion and metabolic condition after resuscitation from hemorrhagic shock. This work was supported by grants R01-HL76182 to AGT, R24–64395, R01–62354, and R01–62318 to MI.

NAD(P)H oxidase contributes to the progression of remote hepatic parenchymal injury and endothelial dysfunction, but not microvascular perfusion deficits

Oxidative stress occurs in remote liver injury, but the origin of the oxidant generation has yet to be thoroughly delineated. Some reports suggest that the source of the distant oxidative stress originates from the site of initial insult [i.e., xanthine oxidase (XO)]; however, it could also be derived from sources such as phagocytic and/or vascular NAD(P)H oxidase (Nox) enzymes. With a murine model of bilateral hindlimb ischemia-reperfusion, we describe here a mechanism for Nox-dependent oxidant production that contributes, at least in part, to remote hepatic parenchymal injury and sinusoidal endothelial cell (SEC) dysfunction. To determine whether Nox enzymes were the source of oxidants, mice were treated immediately after the onset of hindlimb ischemia with specific inhibitors to XO (50 mg/kg ip allopurinol) or Nox (10 mg/kg ip gp91ds-tat and 3 mg/kg ip apocynin). After 1 h of ischemia, hindlimbs were reperfused for either 3 or 6 h. Inhibition of XO failed to provide any improvement in parenchymal injury, SEC dysfunction, neutrophil accumulation, or microvascular dysfunction. In contrast, the inhibition of Nox enzymes prevented the progression (6 h) of parenchymal injury, significantly protected against SEC dysfunction, and completely prevented signs of neutrophil-derived oxidant stress. At the same time, however, inhibition of Nox failed to protect against the early parenchymal injury and microvascular dysfunction at 3 h of reperfusion. These data confirm that microvascular perfusion deficits are not essential for the pathogenesis of remote hepatic parenchymal injury. The data also suggest that Nox enzymes, not XO, are involved in the progression of compromised hepatic parenchymal and endothelial integrity during a systemic inflammatory response.

EARLY DIFFERENCE IN TISSUE PH AND MICROVASCULAR HEMODYNAMICS IN HEMORRHAGIC SHOCK RESUSCITATION USING POLYETHYLENE GLYCOL-ALBUMIN- AND HYDROXYETHYL STARCH-BASED PLASMA EXPANDERS

The hamster chamber window model was subjected to hemorrhagic shock by the withdrawal of 50% of blood volume (BV). BV was restored 1 h after hemorrhage with a single volume infusion (resuscitation) of 25% BV with polyethylene glycol (PEG)-conjugated bovine serum albumin (Alb) and hydroxyethyl starch (HES). Hemorrhage, shock, and resuscitation were monitored continuously in terms of mean arterial pressure (MAP), microvascular blood flow, capillary perfusion, and tissue pH. Blood samples for laboratory parameters were taken at baseline, shock, and resuscitation. Intravascular and tissue pO2 were assessed after resuscitation, and microvascular oxygen supply and extraction were calculated and corrected for pH effect on hemoglobin saturation. Resuscitation with PEG-Alb restored systemic and microvascular parameters up to the end of the observation period (90 min). HES was identical to PEG-Alb resuscitation during the initial 10 to 15 min, but was not sustained subsequently. The trend of recovery in MAP for HES persisted beyond the time when both function capillary density and tissue pH decreased, thus MAP was not indicative of early microvascular dysfunction. Hemoglobin oxygen saturation estimation showed a significant pH dependence. However, oxygen-dependant parameters corrected for pH varied less than 10% from uncorrected data. Early differences found at the microvascular levels suggest that decisions to amend end-result of resuscitation may be short and on the order of minutes. Furthermore, PEG-Alb appears to provide early and long-term sustained systemic and microvascular recovery when used to restitute perfusion and metabolic conditions after resuscitation from hemorrhagic shock.

Early Microvascular Dysfunction in Healthy Normal-Weight Males With Heredity for Type 2 Diabetes

The pathogenesis behind diabetic microangiopathy is complex; both genetic (1–3) and metabolic factors (4–6) are clearly of importance. Recently, it has been demonstrated that not only patients with diabetes but also healthy individuals at risk for diabetes have functional vascular disturbances (7). These findings suggest that factors other than hyperglycemia are of importance for microvascular dysfunction. The aim of the present study was to investigate whether genetic factors (heredity for type 2 diabetes) are associated with disturbances in nutritive skin capillary circulation, nonnutritive skin microcirculation, and/or brachial macrocirculation. Subjects were from the Stockholm Diabetes Prevention Program, a population-based study (8). Normal-weight men who were free of medication, who were nonsmokers, and who had normal oral glucose tolerance tests and insulin sensitivity as assessed by a hyperinsulinemic-euglycemic clamp (9) were investigated. Ten men with heredity for type 2 diabetes were matched for age and BMI with 10 men without heredity. Heredity for type 2 diabetes was defined as known diabetes in at least two second-degree relatives (grandparent, uncle, or aunt) or in at least one first-degree relative in the generation of the proband (sister or brother) or the parents (8). The investigations were performed in the …

Cytokines contribute to early hepatic parenchymal injury and microvascular dysfunction after bilateral hindlimb ischemia

Purpose: Hepatic dysfunction may contribute to death from multiple organ dysfunction after abdominal aortic surgery. Several factors are likely responsible, and the purpose of this study was to determine whether the cytokines tumor necrosis factor-α (TNF-α) and interleukin 1 (IL-1) are involved in initiating this remote hepatic injury. Methods: In a normotensive rat model of 4-hour bilateral hindlimb ischemia/reperfusion (I/R), we measured systemic TNF-α and IL-1 levels throughout the I/R period. Rats were randomly assigned to either the 3-hour control group, the 3-hour I/R group, or the I/R group with administration of a polyclonal antibody (PAb) to TNF-α (I/R + TNF-α PAb). Direct evidence of lethal hepatocyte injury through the labeling of nuclei by propidium iodide (per 10 –1mm 3) and altered microvascular perfusion were assessed by using intravital microscopy. Results: Systemic TNF-α peaked at 83.97 pg/mL ( P < .05, n = 5) at 30 minutes of reperfusion and returned to baseline in 60 to 90 minutes. No significant change in systemic IL-1 was detected ( P < .05, n = 4). Alanine aminotransferase increased 2.5-fold in the I/R group through 3 hours of reperfusion ( P < .05, n = 4), and TNF-α PAb did not attenuate this alanine aminotransferase increase ( P < .05, n = 6). Lethal hepatocyte injury increased by 8-fold in the I/R group compared with the control group ( P < .05, n = 5), whereas TNF-α PAb significantly reduced this injury ( P < .05, n = 4). No regional differences in injury were noted within the acinus. Total perfusion within the microvascular unit did not drop; however, significant flow heterogeneity was observed. The proportion of continuously perfused sinusoids declined in the I/R group after 3 hours of reperfusion in both periportal (62.0 ± 2.2, P < .05) and, to a lesser, although significant, degree, in the pericentral regions (73.2 ± 1.73, P < .05). Conclusion: By scavenging extracellular TNF-α with a PAb, we provide direct evidence that TNF-α contributes to, but is not solely responsible for, early remote hepatocellular injury and microvascular dysfunction. The administration of TNF-α PAb reduced lethal hepatocyte injury in both regions of the acinus and also improved perfusion in the periportal region (76.8 ± 5.41, P < .05), but not in the pericentral region. This suggests that TNF-α released during reperfusion mediates early remote hepatocellular injury and microvascular dysfunction after a remote ischemic insult. (J Vasc Surg 1999;30:533-41.)

Acute peritonitis leads to early remote microvascular dysfunction

Remote organ injury, as evidenced by loss of functional capillaries and impaired microvascular function, has been demonstrated in a resuscitated normotensive 24-h chronic model of intra-abdominal sepsis [1,2]. Our objective has been to develop an acute intra-abdominal model of sepsis which can be used to observe the temporal evolution of this remote microvascular dysfunction.

Selective microvascular endothelial cell dysfunction in the small intestine following resuscitated hemorrhagic shock.

Following resuscitation (RES) from hemorrhagic shock (HEM), intestinal microvessels develop progressive vasoconstriction that impairs mucosal blood flow, despite central hemodynamic RES. These events might have clinical consequences secondary to occult intestinal ischemia. We hypothesized that the microvascular impairments were due to progressive endothelial cell dysfunction and an associated reduction in the dilator, nitric oxide (NO), following HEM/RES. Male Sprague-Dawley rats, were monitored for central hemodynamics and the terminal ileum was studied with in vivo videomicroscopy. HEM was 50% of baseline mean arterial pressure (MAP) for 60 min, and RES was with shed blood + 1 volume of normal saline (NS). Following HEM/RES, acetylcholine (10)(-7), 10(-5) M) was topically applied and ileal inflow (A1) and premucosal arteriolar diameters were measured to assess endothelial-cell function at 60 and 120 min post-RES. Normalization of MAP, cardiac output, and heart rate demonstrated adequate systemic resuscitation. Post-RES vasoconstriction developed in A1 (-25%) and premucosal (-28%) arterioles with an associated reduction in A1 flow (-47%). However, there was a selective impairment of endothelial-dependent dilation that was manifested only in the smaller premucosal arterioles and not in the inflow, A1 arterioles. This suggests that multiple mechanisms are involved in the development of the post-RES vasoconstriction. The premucosal response was likely mediated by endothelial cell dysfunction, while the A1 response was probably the result of enhanced vasoconstrictor forces. This early microvascular dysfunction might contribute to the late sequelae of intestinal ischemia and might alter microvascular responses to subsequent systemic insults.

External detection of early microvascular dysfunction after no-flow ischemia followed by reperfusion in isolated rabbit hearts.

To define relationships better between the duration of severe ischemia and microvascular functional integrity with an approach potentially applicable to studies in vivo, the effects of 30 and 60 minutes of global, no-flow ischemia on the coronary vasculature of isolated, perfused rabbit hearts were determined. Residue-detection data, analyzed with a two-compartment model, were used to estimate indices of microvascular function, including the mean-transit time (tBSA) of radiolabeled bovine serum albumin (125I-BSA), vascular into extravascular space clearance, and vascular and extravascular space volumes. It was shown that the Central Volume Principle of tracer kinetics does not hold when transport of label between vascular and extravascular spaces takes place convectively by solvent drag, and a more general expression for tBSA was derived and applied. Left ventricular end-diastolic pressure and left ventricular developed pressure were monitored with an isovolumic balloon. Aortic perfusion pressure, left ventricular end-diastolic pressure, left ventricular developed pressure and vascular space volume remained constant, while mean transit time, vascular into extravascular space clearance and extravascular space volumes increased gradually during 3-hour control perfusions. Perfusion pressure, mean transit time and extravascular space clearance increased significantly with reperfusion after 30 minutes of ischemia even though left ventricular end-diastolic and left ventricular-developed pressures returned to control levels. Vascular space volumes increased minimally, whereas extravascular space volumes increased 5-fold during reperfusion. These changes in 125I-BSA washout and permeation across endothelium with reperfusion after no-flow ischemia indicate that compromised vascular integrity is an early manifestation of ischemia with functional consequences that persist even after ischemia sufficiently brief to permit restoration of left ventricular performance.

Transport of large molecules from plasma to interstitial fluid and lymph in dogs.

Transport of large molecules from plasma to interstitial fluid and lymph in dogs.