Ischemia, hyperemia, exercise, and nitric oxide. Complex physiology and complex molecular adaptations

Spectral Analysis of Muscle Hemodynamic Responses in Post-Exercise Recovery Based on Near-Infrared Spectroscopy

Spectral analysis of blood flow or blood volume oscillations can help to understand the regulatory mechanisms of microcirculation. This study aimed to explore the relationship between muscle hemodynamic response in the recovery period and exercise quantity. Fifteen healthy subjects were required to perform two sessions of submaximal plantarflexion exercise. The blood volume fluctuations in the gastrocnemius lateralis were recorded in three rest phases (before and after two exercise sessions) using near-infrared spectroscopy. Wavelet transform was used to analyze the total wavelet energy of the concerned frequency range (0.005–2 Hz), which were further divided into six frequency intervals corresponding to six vascular regulators. Wavelet amplitude and energy of each frequency interval were analyzed. Results showed that the total energy raised after each exercise session with a significant difference between rest phases 1 and 3. The wavelet amplitudes showed significant increases in frequency intervals I, III, IV, and V from phase 1 to 3 and in intervals III and IV from phase 2 to 3. The wavelet energy showed similar changes with the wavelet amplitude. The results demonstrate that local microvascular regulators contribute greatly to the blood volume oscillations, the activity levels of which are related to the exercise quantity.

Imaging the Landmarks of Vascular Recovery

Background: Peripheral arterial disease (PAD) is a major worldwide health concern. Since the late 1990s therapeutic angiogenesis has been investigated as an alternative to traditional PAD treatments. Although positive preclinical results abound in the literature, the outcomes of human clinical trials have been discouraging. Among the challenges the field has faced has been a lack of standardization of the timings and measures used to validate new treatment approaches.

Methods: In order to study the spatiotemporal dynamics of both perfusion and neovascularization in mice subjected to surgically-induced hindlimb ischemia (n= 30), we employed three label-free imaging modalities (a novel high-sensitivity ultrasonic Power Doppler methodology, laser speckle contrast, and photoacoustic imaging), as well as a tandem of radio-labeled molecular probes, ^99mTc-NC100692 and ^99mTc-BRU-5921 respectively, designed to detect two key modulators of angiogenic activity, α_Vβ₃ and HIF-1α , via scintigraphic imaging.

Results: The multimodal imaging strategy reveals a set of “landmarks”—key physiological and molecular events in the healing process—that can serve as a standardized framework for describing the impact of emerging PAD treatments. These landmarks span the entire process of neovascularization, beginning with the rapid decreases in perfusion and oxygenation associated with ligation surgery, extending through pro-angiogenic changes in gene expression driven by the master regulator HIF-1α , and ultimately leading to complete functional revascularization of the affected tissues.

Conclusions: This study represents an important step in the development of multimodal non-invasive imaging strategies for vascular research; the combined results offer more insight than can be gleaned through any of the individual imaging methods alone. Researchers adopting similar imaging strategies and will be better able to describe changes in the onset, duration, and strength of each of the landmarks of vascular recovery, yielding greater biological insight, and enabling more comprehensive cross-study comparisons. Perhaps most important, this study paves the road for more efficient translation of PAD research; emerging experimental treatments can be more effectively assessed and refined at the preclinical stage, ultimately leading to better next-generation therapies.

Menopausal hot flashing and endothelial function in two vascular beds: findings from a cross-sectional study of postmenopausal women

OBJECTIVE

We sought to examine the association of menopausal hot flashing with vascular reactivity in two different vascular beds in the same cohort of postmenopausal women and explore the relationship between hot flashing and cardiovascular disease (CVD) risk profile.

METHODS

A cross-sectional study of 79 healthy postmenopausal women, 23 of whom have never had menopausal hot flashes and 56 of whom have reported hot flashes. Endothelial function at a microvascular level was measured with Laser Doppler Imaging with Iontophoresis which assesses the response to both acetylcholine (Ach, endothelium dependent) and sodium-nitroprusside (SNP, endothelium independent). Reactive Hyperemia Index (RHI) was measured with peripheral arterial tonometry as a marker of endothelial function mainly at a macrovascular level. Metabolic biomarkers including insulin sensitivity were assessed.

RESULTS

Women with hot flashes had enhanced microvascular response to Ach by ∼30% (P = 0.04) and to SNP by ∼31% (P = 0.02), but lower RHI by ∼13% (P = 0.05) compared with women without flashes. Hot flashing was associated with enhanced response to SNP and lower RHI after adjustment for confounders and conventional CVD risk factors. Women with hot flashes were more insulin resistant than nonflashers (HOMAIR: 1.9 (1.2-2.6) vs 1.4 (0.8-1.9), P = 0.03).

CONCLUSIONS

Our data support the association of hot flashing with greater insulin resistance and lower macrovascular response. The paradoxical enhanced microvascular response in hot flashers could be the result of the net effect of thermoregulatory and nonnitric oxide-related pathways rather than of endothelial integrity.

Exercise and Cardioprotection: A Natural Defense Against Lethal Myocardial Ischemia-Reperfusion Injury and Potential Guide to Cardiovascular Prophylaxis

Similar to ischemic preconditioning, high-intensity exercise has been shown to decrease infarct size following myocardial infarction. In this article, we review the literature on beneficial effects of exercise, exercise requirements for cardioprotection, common methods utilized in laboratories to study this phenomenon, and discuss possible mechanisms for exercise-mediated cardioprotection.

Impact of Blood Flow Restriction Exercise on Muscle Fatigue Development and Recovery

PURPOSE

The present study was designed to provide mechanistic insight into the time course and etiology of muscle fatigue development and recovery during and after low-intensity exercise when it is combined with blood flow restriction (BFR).

METHODS

Seventeen resistance-trained males completed four sets of low-intensity isotonic resistance exercise under two experimental conditions: knee extension exercise (i) with BFR and (ii) without BFR (CON). Neuromuscular tests were performed before, during (immediately after each set of knee extension exercise), and 1, 2, 4, and 8 min after each experimental condition. Maximal voluntary torque, quadriceps twitch torque in response to paired electrical stimuli at 10 Hz (PS10) and 100 Hz (PS100), PS10·PS100 ratio as an index of low-frequency fatigue, and voluntary activation were measured under isometric conditions. Perceptual and EMG data were recorded during each exercise condition.

RESULTS

After the first set of exercise, BFR induced significantly greater reductions in maximal voluntary torque, PS100, and PS10·PS100 ratio compared with CON. These parameters progressively declined throughout the BFR protocol but recovered substantially within 2 min postexercise when blood flow was restored. Neither a progressive decline in the course of the exercise protocol nor a substantial recovery of these parameters occurred during and after CON. Only at exercise termination, voluntary activation differed significantly between BFR and CON with greater reductions during BFR.

CONCLUSION

At the early stage of exercise, BFR exacerbated the development of muscle fatigue mainly due to a pronounced impairment in contractile function. Despite the high level of muscle fatigue during BFR exercise, the effect of BFR on muscle fatigue was diminished after 2 min of reperfusion, suggesting that BFR has a strong but short-lasting effect on neuromuscular function.

Combined effects of aquaporin-4 and hypoxia produce age-related hydrocephalus

Aquaporin-4, present in ependymal cells, in glia limiting and abundantly in pericapillary astrocyte foot processes, and aquaporin-1, expressed in choroid plexus epithelial cells, play an important role in cerebrospinal fluid production and may be involved in the pathophysiology of age-dependent hydrocephalus. The finding that brain aquaporins expression is regulated by low oxygen tension led us to investigate how hypoxia and elevated levels of cerebral aquaporins may result in an increase in cerebrospinal fluid production that could be associated with a hydrocephalic condition. Here we have explored, in young and aged mice exposed to hypoxia, whether aquaporin-4 and aquaporin-1 participate in the development of age-related hydrocephalus. Choroid plexus, striatum, cortex and ependymal tissue were analyzed separately both for mRNA and protein levels of aquaporins. Furthermore, parameters such as total ventricular volume, intraventricular pressure, cerebrospinal fluid outflow rate, ventricular compliance and cognitive function were studied in wild type, aquaporin-1 and aquaporin-4 knock-out animals subjected to hypoxia or normoxia. Our data demonstrate that hypoxia is involved in the development of age-related hydrocephalus by a process that depends on aquaporin-4 channels as a main route for cerebrospinal fluid movement. Significant increases in aquaporin-4 expression that occur over the course of animal aging, together with a reduced cerebrospinal fluid outflow rate and ventricular compliance, contribute to produce more severe hydrocephalus related to hypoxic events in aged mice, with a notable impairment in cognitive function. These results indicate that physiological events and/or pathological conditions presenting with cerebral hypoxia/ischemia contribute to the development of chronic adult hydrocephalus.

Prognostic Value of Flow-Mediated Vasodilation in Brachial Artery and Fingertip Artery for Cardiovascular Events: A Systematic Review and Meta-Analysis

BACKGROUND

Endothelial dysfunction plays a pivotal role in cardiovascular disease progression, and is associated with adverse events. The purpose of this systematic review and meta-analysis was to investigate the prognostic magnitude of noninvasive peripheral endothelial function tests, brachial artery flow-mediated dilation (FMD), and reactive hyperemia--peripheral arterial tonometry (RH-PAT) for future cardiovascular events.

METHODS AND RESULTS

Databases of MEDLINE, EMBASE, and the Cochrane Library were systematically searched. Clinical studies reporting the predictive value of FMD or RH-PAT for cardiovascular events were identified. Two authors selected studies and extracted data independently. Pooled effects were calculated as risk ratio (RR) for continuous value of FMD and natural logarithm of RH-PAT index (Ln_RHI) using random-effects models. Thirty-five FMD studies of 17 280 participants and 6 RH-PAT studies of 1602 participants were included in the meta-analysis. Both endothelial function tests significantly predicted cardiovascular events (adjusted relative risk [95% CI]: 1% increase in FMD 0.88 [0.84-0.91], P<0.001, 0.1 increase in Ln_RHI 0.79 [0.71-0.87], P<0.001). There was significant heterogeneity in the magnitude of the association across studies. The magnitude of the prognostic value in cardiovascular disease subjects was comparable between these 2 methods; a 1 SD worsening in endothelial function was associated with doubled cardiovascular risk.

CONCLUSIONS

Noninvasive peripheral endothelial function tests, FMD and RH-PAT, significantly predicted cardiovascular events, with similar prognostic magnitude. Further research is required to determine whether the prognostic values of these 2 methods are independent of each other and whether an endothelial function-guided strategy can provide benefit in improving cardiovascular outcomes.

Further Peripheral Vascular Dysfunction in Heart Failure Patients With a Continuous-Flow Left Ventricular Assist Device: The Role of Pulsatility

OBJECTIVES

Using flow-mediated vasodilation (FMD) and reactive hyperemia (RH), this study aimed to provide greater insight into left ventricular assist device (LVAD)-induced changes in peripheral vascular function.

BACKGROUND

Peripheral endothelial function is recognized to be impaired in patients with heart failure with reduced ejection fraction (HFrEF), but the peripheral vascular effects of continuous-flow LVAD implantation, now used as either a bridge to transplantation or as a destination therapy, remain unclear.

METHODS

Sixty-eight subjects (13 New York Heart Association [NYHA] functional class II HFrEF patients, 19 NYHA functional class III/IV HFrEF patients, 20 NYHA functional class III/IV HFrEF patients post-LVAD implantation, and 16 healthy age-matched control subjects) underwent FMD and RH testing in the brachial artery with blood flow velocity, artery diameters, and pulsatility index (PI) assessed by ultrasound Doppler.

RESULTS

PI was significantly lower in the LVAD group (2.0 ± 0.4) compared with both the HFrEF II (8.6 ± 0.8) and HFrEF III/IV (8.1 ± 0.9) patients, who, in turn, had significantly lower PI than the control subjects (12.8 ± 0.9). Likewise, LVAD %FMD/shear rate (0.09 ± 0.01 %Δ/s(-1)) was significantly reduced compared with all other groups (control subjects, 0.24 ± 0.03; HFrEF II, 0.17 ± 0.02; and HFrEF III/IV, 0.13 ± 0.02 %Δ/s(-1)), and %FMD/shear rate significantly correlated with PI (r = 0.45). RH was unremarkable across groups.

CONCLUSIONS

Although central hemodynamics are improved in patients with HFrEF by a continuous-flow LVAD, peripheral vascular function is further compromised, which is likely due, at least in part, to the reduction in pulsatility that is a characteristic of such a mechanical assist device.

Predictive value of endothelial function by noninvasive peripheral arterial tonometry for coronary artery disease

BACKGROUND

Endothelial dysfunction is a key step in the initiation and progression of atherosclerosis and subsequent cardiovascular complications. We examined whether peripheral endothelial function, as assessed by fingertip reactive hyperemia-peripheral arterial tonometry (RH-PAT), can provide additional clinical value to traditional risk factors for cardiovascular diseases in predicting coronary artery disease (CAD).

METHODS

We included 118 stable patients who were referred for coronary angiography for chest pain evaluation or due to abnormal stress test results. A natural logarithmic value of the RH-PAT index (Ln_RHI) was obtained before cardiac catheterization by an independent operator. Significant CAD was defined as luminal stenosis of at least 70% (≥50% at left main) and/or fractional flow reserve of up to 0.80 in one or more major coronary arteries or their major branches.

RESULTS

Levels of Ln_RHI were significantly lower in patients with CAD (n=60) compared with patients without CAD (n=58; 0.69±0.29 vs. 0.88±0.27, P<0.001). Ln_RHI was significantly associated with CAD independent from traditional risk factors (odds ratio for a 0.1 decrease in Ln_RHI=1.25, 95% confidence interval: 1.04-1.52, P=0.01). The net reclassification index was improved when Ln_RHI was added to traditional risk factors (0.62, 95% confidence interval: 0.27-0.97, P=0.001).

CONCLUSION

Peripheral endothelial function, as assessed by RH-PAT, improved risk stratification when added to traditional risk factors. RH-PAT is potentially useful for identifying patients at high risk for CAD.

Secondary prevention strategy of cardiovascular disease using endothelial function testing

Over the past decades, secondary prevention of cardiovascular (CV) disease has improved and considerably reduced mortality rates. However, there remains a high-rate of new or recurrent CV events in those with established atherosclerotic vascular diseases. Although most of the prevailing therapies target the conventional risk factors, there is notable interindividual heterogeneity in adaptation to risk factors and response to therapies, which affects efficacy. It is desirable to have a methodology for directly assessing the functional significance of atherogenesis, and for managing individual patients based on their comprehensive vascular health. Endothelial function plays a pivotal role in all stages of atherosclerosis, from initiation to atherothrombotic complication. Endothelial function reflects the integrated effect of all the atherogenic and atheroprotective factors present in an individual, and is therefore regarded as an index of active disease process and a significant risk factor for future CV events. Moreover, improvement in endothelial function is associated with decreased risk of CV events, even in the secondary prevention setting. The introduction of endothelial function assessment into clinical practice may trigger the development of a more tailored and personalized medicine and improve patient outcomes. In this review, we summarize current knowledge on the contribution of endothelial dysfunction to atherosclerotic CV disease in the secondary prevention setting. Finally, we focus on the potential of an endothelial function-guided management strategy in secondary prevention.

Noninvasive monitoring of small intestinal oxygen in a rat model of chronic mesenteric ischemia

We noninvasively monitored the partial pressure of oxygen (pO2) in rat's small intestine using a model of chronic mesenteric ischemia by electron paramagnetic resonance oximetry over a 7-day period. The particulate probe lithium octa-n-butoxynaphthalocyanine (LiNc-BuO) was embedded into the oxygen permeable material polydimethyl siloxane by cast-molding and polymerization (Oxy-Chip). A one-time surgical procedure was performed to place the Oxy-Chip on the outer wall of the small intestine (SI). The superior mesenteric artery (SMA) was banded to ~30% of blood flow for experimental rats. Noninvasive measurement of pO2 was performed at the baseline for control rats or immediate post-banding and on days 1, 3, and 7. The SI pO2 for control rats remained stable over the 7-day period. The pO2 on day-7 was 54.5 ± 0.9 mmHg (mean ± SE). SMA-banded rats were significantly different from controls with a noted reduction in pO2 post banding with a progressive decline to a final pO2 of 20.9 ± 4.5 mmHg (mean ± SE; p = 0.02). All SMA-banded rats developed adhesions around the Oxy-Chip, yet remained asymptomatic. The hypoxia marker Hypoxyprobe™ was used to validate the low tissue pO2. Brown cytoplasmic staining was consistent with hypoxia. Mild brown staining was noted predominantly on the villus tips in control animals. SMA-banded rats had an extended region of hypoxic involvement in the villus with a higher intensity of cytoplasmic staining. Deep brown stainings of the enteric nervous system neurons and connective tissue both within layers and in the mesentery were noted. SMA-banded rats with lower pO2 values had a higher intensity of staining. Thus, monitoring SI pO2 using the probe Oxy-Chip provides a valid measure of tissue oxygenation. Tracking pO2 in conditions that produce chronic mesenteric ischemia will contribute to our understanding of intestinal tissue oxygenation and how changes impact symptom evolution and the trajectory of chronic disease.

Vascular function and the role of oxidative stress in heart failure, heart transplant, and beyond

Using flow-mediated vasodilation (FMD), reactive hyperemia, and an acute oral antioxidant cocktail (AOC; vitamins C and E and α-lipoic acid), this study aimed to provide greater insight into altered vascular function and the role of oxidative stress in chronic heart failure patients with reduced ejection fraction (HFrEF) and at several time points beyond heart transplantation (HTx). A total of 61 age-matched subjects (12 healthy controls, 14 New York Heart Association class II and III HFrEF, and 35 HTx recipients [<3 years post-HTx, 5-10 years post-HTx, and >14 years post-HTx]) ingested either placebo (PL) or an AOC before FMD and reactive hyperemia testing of the brachial artery. Vascular function, as measured by FMD, was not different among the controls (6.8±1.9%), recent <3-year post-HTx group (8.1±1.2%), and the 5- to 10-year post-HTx group (5.5±1.0%). However, PL FMD was lower in the HFrEF (4.5±0.7%) and in the >14-year post-HTx group (2.9±0.8%). The AOC increased plasma ascorbate levels in all of the groups but only increased FMD in the controls (PL, 6.8±1.9%; AOC, 9.2±1.0%) and >14-year post-HTx recipients (PL, 2.9±0.8%; AOC, 4.5±1.3%). There were no differences in reactive hyperemia in any of the groups with PL or AOC. This cross-sectional study reveals that, compared with controls, vascular function is blunted in HFrEF, is similar soon after HTx, but is decreased with greater time post-HTx with free radicals implicated in this progression.

Peripheral endothelial dysfunction in patients suffering from acute schizophrenia: a potential marker for cardiovascular morbidity?

Patients suffering from schizophrenia have an increased standardized ratio for cardiovascular mortality compared to the general population. Endothelial function was identified as a prominent parameter for cardiac risk stratification in patients with heart disease. Here, we aimed to analyze the reactivity of the microcirculation applying the post-occlusive reactive hyperemia (PORH) test and spectral analysis of skin vasomotion as markers of endothelial function. We investigated 21 unmedicated patients suffering from paranoid schizophrenia as well as 21 matched controls. The capillary blood flow was assessed on the right forearm after compression of the brachial artery. Parameters of PORH such as time to peak (TP) or PORH index were calculated. In addition, spectral analysis of skin vasomotion was performed and five frequency bands (endothelial, sympathetic, vascular myogenic, respiratory and heart beat activity) were studied. Psychotic symptoms were quantified using the Positive and Negative Syndrome Scale (PANSS) and correlated to the parameters obtained. We report a blunted hyperemic response in patients after occlusion of the brachial artery indicated by significantly increased TP and decreased PORH indices. In contrast, vasomotion as investigated by spectral analysis of skin flow was rather sparsely altered showing differences at rest for the sympathetic and cardiac components only. Our results are suggestive of peripheral endothelial dysfunction in unmedicated patients suffering from schizophrenia. Future, prospective studies should address the relation of endothelial dysfunction to cardiac morbidity in patients with schizophrenia.

Relation of brachial and digital measures of vascular function in the community: the Framingham heart study

Impaired vascular function contributes to the development of clinical cardiovascular disease. The relation between vasodilator function assessed noninvasively in the brachial and digital arteries remains incompletely defined. In the Framingham Offspring, Third Generation and Omni Cohorts, we measured flow-mediated dilation (FMD; n = 7031; age 48 ± 13 years; age range, 19 to 88 years; 54% women) and peripheral arterial tonometry (PAT) ratio (n = 4352; 55 ± 16 years; age range, 19 to 90 years; 51% women). Abnormal vascular function for each measure was defined by the sex-specific fifth percentile in a reference group free of conventional cardiovascular risk factors. The prevalence of abnormal FMD but not abnormal PAT ratio was higher with advancing age. In multivariable models, higher body mass index was associated with a higher prevalence of both abnormal FMD and PAT ratio. Additional correlates of abnormal FMD included increasing age and higher systolic blood pressure. In contrast, correlates of abnormal PAT ratio included lower systolic blood pressure, increasing total/high-density lipoprotein cholesterol ratio, diabetes, smoking, and lipid-lowering medication. Whereas women had higher FMD and PAT ratios compared with men, using sex-specific reference values, women had a higher prevalence of abnormal brachial and digital vascular function. In participants who had concurrent testing (n = 1843), PAT ratio was not significantly associated with FMD in multivariable models. In this large, community-based cohort, brachial and digital measures of vascular function had differing relations with cardiovascular risk factors and were nearly uncorrelated with each other. These results suggest that FMD and PAT provide distinct information regarding vascular function in conduit versus smaller digital vessels.

Does endothelial dysfunction contribute to the clinical status of patients with peripheral arterial disease?

Peripheral arterial disease leads to lower extremity ischemia and limb loss, and is linked to cardiovascular events. The anatomical extent of lower extremity atherosclerosis fails to fully explain ischemic symptoms or predict the development of critical limb ischemia. Endothelial dysfunction is known to contributed to the pathogenesis and clinical expression of coronary artery disease, but the importance of endothelial dysfunction in peripheral arterial disease remains incompletely understood. Endothelial dysfunction could contribute to lower extremity ischemia by impairing blood flow responses to ischemia, collateral formation and arterial remodelling, and by promoting vasospasm, thrombosis, plaque rupture and lesion progression. There is a need for additional studies examining the contribution of endothelial dysfunction to the pathogenesis of peripheral arterial disease, and the potential role of endothelial dysfunction as a surrogate marker with utility in the management of patients.

Endothelial dysfunction in diabetes mellitus: molecular mechanisms and clinical implications

Cardiovascular disease is a major complication of diabetes mellitus, and improved strategies for prevention and treatment are needed. Endothelial dysfunction contributes to the pathogenesis and clinical expression of atherosclerosis in diabetes mellitus. This article reviews the evidence linking endothelial dysfunction to human diabetes mellitus and experimental studies that investigated the responsible mechanisms. We then discuss the implications of these studies for current management and for new approaches for the prevention and treatment of cardiovascular disease in patients with diabetes mellitus.

Relationship between brachial artery flow-mediated dilatation, hyperemic shear stress, and the metabolic syndrome

Abstract

Metabolic syndrome (MetSyn) may predispose to cardiovascular disease (CVD) by causing vascular dysfunction. This study aimed to determine the association of MetSyn with vascular function, as assessed by brachial artery flow-mediated dilatation (FMD) and hyperemic shear stress (HSS). A total of 1,417 male firefighters without established diabetes and CVD were classified for MetSyn, according to the National Cholesterol Education Program Adult Treatment Panel III (NCEP) definition. MetSyn was present in 267 individuals (19%). Although FMD was lower in those with versus without MetSyn (8.1 ± 4.1 vs 8.7 ± 4.0%; p = 0.02), this was not significant after adjusting for baseline differences (age, smoking, and brachial artery diameter) ( p = 0.2). However, HSS was significantly lower in those with versus without MetSyn (72.0 ± 27.8 vs 80.9 ± 24.8 dyne/cm2; p < 0.001), and there was a significant inverse graded relationship with the number of NCEP criteria present (mean HSS for those with 0, 1, 2, 3, 4, and 5 criteria: 83.2 ± 22.5, 82.2 ± 24.7, 76.5 ± 27.2, 74.3 ± 27.4, 66.5 ± 28.4, 67.1 ± 27.6 dyne/cm2; p < 0.001 for trend). The individual NCEP criteria of abdominal obesity, systolic hypertension, and impaired fasting glucose were independent predictors for HSS. In conclusion, MetSyn was not associated with impaired FMD. Alternatively, HSS, a measure of microvascular function, was significantly lower in those with MetSyn. Thus, MetSyn may contribute to CVD by causing microvascular dysfunction.

Physical inactivity rapidly induces insulin resistance and microvascular dysfunction in healthy volunteers

OBJECTIVE

Sedentary lifestyle increases the risk of cardiovascular disease and diabetes. Vascular dysfunction contributes to atherogenesis and has been linked to insulin resistance.

METHODS AND RESULTS

We measured insulin sensitivity by glucose tolerance test and vascular function by ultrasound and venous occlusion plethysmography in 20 healthy subjects (14 men, 6 women) at baseline and during 5 days of bed rest. Bed rest led to a 67% increase in the insulin response to glucose loading (P<0.001) suggesting increased insulin resistance and produced increases in total cholesterol and triglycerides. Bed rest led to decreased reactive hyperemia in the forearm (1317+/-404 to 1112+/-260 mL/min, P=0.01) and the calf (28.5+/-7.0 to 22.2+/-8.7 mL/min/dL, P=0.003) indicating impaired microvascular function. Bed rest decreased brachial artery diameter and increased systolic blood pressure suggesting increased basal arterial tone. There were no changes in circulating inflammatory markers arguing against systemic inflammation as a mechanism for vascular dysfunction in this setting.

CONCLUSIONS

Physical inactivity was associated with the development of insulin resistance, dyslipidemia, increased blood pressure, and impaired microvascular function in healthy volunteers. Our findings may provide insight into the pathogenesis of vascular disease in sedentary individuals and emphasize that even short-term physical inactivity may have adverse metabolic and vascular consequences.

Predictive value of reactive hyperemia for cardiovascular events in patients with peripheral arterial disease undergoing vascular surgery

OBJECTIVE

Reactive hyperemia is the compensatory increase in blood flow that occurs after a period of tissue ischemia, and this response is blunted in patients with cardiovascular risk factors. The predictive value of reactive hyperemia for cardiovascular events in patients with atherosclerosis and the relative importance of reactive hyperemia compared with other measures of vascular function have not been previously studied.

METHODS AND RESULTS

We prospectively measured reactive hyperemia and brachial artery flow-mediated dilation by ultrasound in 267 patients with peripheral arterial disease referred for vascular surgery (age 66+/-11 years, 26% female). Median follow-up was 309 days (range 1 to 730 days). Fifty patients (19%) had an event, including cardiac death (15), myocardial infarction (18), unstable angina (8), congestive heart failure (6), and nonhemorrhagic stroke (3). Patients with an event were older and had lower hyperemic flow velocity (75+/-39 versus 95+/-50 cm/s, P=0.009). Patients with an event also had lower flow-mediated dilation (4.5+/-3.0 versus 6.9+/-4.6%, P<0.001), and when these 2 measures of vascular function were included in the same Cox proportional hazards model, lower hyperemic flow (OR 2.7, 95% CI 1.2 to 5.9, P=0.018) and lower flow-mediated dilation (OR 4.2, 95% CI: 1.8 to 9.8, P=0.001) both predicted cardiovascular events while adjusting for other risk factors.

CONCLUSIONS

Thus, lower reactive hyperemia is associated with increased cardiovascular risk in patients with peripheral arterial disease. Furthermore, flow-mediated dilation and reactive hyperemia incrementally relate to cardiovascular risk, although impaired flow-mediated dilation was the stronger predictor in this population. These findings further support the clinical relevance of vascular function measured in the microvasculature and conduit arteries in the upper extremity.

Does coronary vasodilation after adenosine override endothelin-1-induced coronary vasoconstriction?

Endothelin-1 is a powerful coronary vasoconstrictor that is overexpressed in coronary artery disease. Adenosine is a powerful coronary vasodilator used for myocardial perfusion imaging to identify flow-limiting coronary artery stenosis. Therefore, in an animal model we tested the hypothesis that intracoronary endothelin-1 may cause myocardial perfusion abnormalities by positron emission tomography (PET) at resting conditions that may persist or only partially improve after intravenous adenosine stress in the absence of myocardial scar and flow-limiting stenosis. Fourteen dogs underwent serial PET perfusion imaging with rubidium-82 before and after subselective intracoronary infusion of endothelin-1, followed by intravenous and then intracoronary adenosine. Small physiological doses of endothelin-1 infused into the mid-left circumflex coronary artery caused quantitatively significant resting perfusion abnormalities that normalized after intracoronary adenosine but not consistently after intravenous adenosine used for diagnostic imaging. After effects of adenosine abated, resting perfusion defects returned, lasting up to 5 h in some animals. Cumulative doses of endothelin-1 caused perfusion defects that did not normalize after intravenous adenosine. In an animal model without myocardial scar or flow-limiting stenosis, intracoronary endothelin-1 causes visually apparent, quantitatively significant, long-lasting myocardial perfusion defects at resting conditions that may persist or only partially improve after intravenous adenosine used for diagnostic imaging. These results may potentially explain resting perfusion abnormalities or heterogeneity by clinical PET that may persist or only partially improve after adenosine stress perfusion imaging in the absence of myocardial scar and flow-limiting stenosis.

Does Handgrip Exercise Training Increase Forearm Ischemic Vasodilator Responses in Patients Receiving Hemodialysis?

In patients receiving hemodialysis, exercise capacity is extremely limited. Although vasodilation is one of the key phenomena for blood perfusion into working skeletal muscles during exercise, it is not clear whether the vasodilator capacity is increased after physical training in this population. We attempted to clarify whether handgrip exercise training increases forearm vasodilator responses to arterial occlusion, and to determine the relationship between muscle contraction function and the vasodilator responses in patients receiving hemodialysis. Eight patients and 7 age-matched healthy controls were tested. The patients participated in handgrip training four times a week for 6 weeks. Before and after the training the maximum muscle strength and endurance were measured with a handgrip dynamometer, and the forearm vasodilator responses to 3-minute arterial occlusion were measured by the near infrared spectroscopy technique. Maximum strength and endurance were significantly lower in the patients than in the controls. Maximum strength (from 183+/-84 to 228+/-92 Newtons, p<0.05) and endurance (from 19+/-6 to 31+/-8 sec, p<0.05) were both increased after the training in the patients. Vasodilator responses estimated by the ratio of the maximum value of oxyhemoglobin after relief of arterial occlusion to its minimum value before the relief were significantly smaller in the patients compared with those in the controls (132+/-20 vs 161+/-27%, p<0.05). In contrast to the findings in muscle function, the decreased vasodilator responses were not improved after the training (141+/-17%). Additionally, no improvement in the vasodilator responses was observed in the parameters estimated by oxygen saturation. These data suggest that exercise capacity increased by physical training is produced by the functional improvement of skeletal muscles per se, but not by alterations in blood perfusion for oxygenation of the muscles in patients receiving hemodialysis.

Effect of leptin on renal ischemia-reperfusion damage in rats

Tumor necrosis factor-alpha (TNF-alpha) has been established as an important mediator in renal ischemia-reperfusion (I/R) injury. Leptin, a product of the ob gene, has been known to exhibit cytoprotective effects on renal tissue, but its effect on renal tissue TNF-alpha level after renal I/R injury in rats remains unknown. The purpose of the study was to evaluate the effects of leptin on renal tissue TNF-alpha, malondialdehyde (MDA), protein carbonyls (PCs) and total sulfydryl group (SH) levels, and plasma nitrite levels after renal I/R injury in rats. The animals were divided into three groups: control, I/R and I/R+leptin. Rats were subjected to renal ischemia by clamping the left pedicle for 45 min, and then reperfused for 1 h. The I/R+leptin group was pretreated intraperitoneally with leptin (10 microg/kg) 30 min before the induction of ischemia. Our results indicate that MDA, TNF-alpha levels, and PCs were significantly higher in the I/R group than those in the control group (p < 0.05). The administration of leptin decreased these parameters (p < 0.05) significantly. The SH level was observed to significantly decrease after I/R injury when compared to the control group (p < 0.05). Leptin treatment significantly increased tissue SH and plasma nitrite levels when compared to the I/R group (p < 0.05). Plasma nitrite levels did not change significantly in I/R when compared to the control. These results suggest that leptin could exert a protective effect on I/R induced renal damage by decreasing TNF-alpha levels and increasing nitrite level.

eNOS T-786C Genotype, Physical Activity, and Peak Forearm Blood Flow in Females

BACKGROUND

The purpose of the present study was to determine interactive and main effects of the eNOS T-786C gene polymorphism and habitual physical activity level on forearm vascular resistance (FVR) and forearm blood flow (FBF) at rest and during 3 min of reactive hyperemia.

METHODS

We studied healthy, Caucasian (age 25 +/- 1 yr), sedentary (maximal oxygen consumption, [OV0312]O2max: 33.8 +/- 1 mL x kg(-1)x min(-1)), and endurance-trained ([OV0312]O2max: 45.3 +/- 1 mL x kg(-1)x min(-1)) women. FBF was measured using venous occlusion plethysmography before (resting) and after 5 min of arm arterial occlusion at 1 (peak vasodilation), 2, and 3 min of reactive hyperemia. [OV0312]O2max was measured using a standard treadmill protocol, and skinfolds were measured to estimate body composition.

RESULTS

There was a significant interaction between eNOS genotype and physical activity level on resting FVR (P = 0.0003). Sedentary subjects with the TT genotype had the lowest resting FVR, but among the endurance-trained group, the TC+CC genotype group had the lowest resting FVR. This interaction was reflected in the resting FBF values (P = 0.03). After accounting for important covariates, there was a main effect of eNOS genotype on peak FBF (TT, 7.0 +/- 0.3 vs TC+CC, 5.9 +/- 0.4 mL x 100 mL(-1) FAV x min(-1), P = 0.03) and the percent decrease in FVR (TT, -62 +/- 2 vs TC+CC, -51 +/- 4%, P = 0.04) at minute 1.

CONCLUSIONS

These results of the interactive effects suggest that young females possessing a C allele may reduce their resting FVR by improving their cardiovascular fitness level, but TT homozygotes, who may have normal eNOS gene function, may not improve their resting FVR with improvements in cardiovascular fitness. Furthermore, regardless of physical activity level, the TT genotype showed a favorable hemodynamic response during reactive hyperemia compared with the C allele carriers.

Inhibition of vascular ATP-sensitive K+ channels does not affect reactive hyperemia in human forearm

The extent to which ATP-sensitive K(+) channels contribute to reactive hyperemia in humans is unresolved. We examined the role of ATP-sensitive K(+) channels in regulating reactive hyperemia induced by 5 min of forearm ischemia. Thirty-one healthy subjects had forearm blood flow measured with venous occlusion plethysmography. Reactive hyperemia could be reproducibly induced (n = 9). The contribution of vascular ATP-sensitive K(+) channels to reactive hyperemia was determined by measuring forearm blood flow before and during brachial artery infusion of glibenclamide, an ATP-sensitive K(+) channel inhibitor (n = 12). To document ATP-sensitive K(+) channel inhibition with glibenclamide, coinfusion with diazoxide, an ATP-sensitive K(+) channel opener, was undertaken (n = 10). Glibenclamide did not significantly alter resting forearm blood flow or the initial and sustained phases of reactive hyperemia. However, glibenclamide attenuated the hyperemic response induced by diazoxide. These data suggest that ATP-sensitive K(+) channels do not play an important role in controlling forearm reactive hyperemia and that other mechanisms are active in this adaptive response.

The effects of resistance exercise on skeletal muscle abnormalities in patients with advanced heart failure

Resistance exercise increases muscular strength and endurance, which prevents injuries associated with musculoskeletal disorders, favorably alters muscle fiber type distribution, and up-regulates the genetic expression of certain enzymes seen in dysfunctional skeletal muscles. Although the benefits of resistance exercise are well documented in the literature, this form of exercise is not routinely recommended for patients with heart failure for fear of symptom exacerbation, and because of poor understanding of how best to prescribe this type of exercise. Because muscle atrophy and deconditioning states are common findings in patients with heart failure, these patients stand to benefit substantially from resistance training because this type of physical activity results in functional adaptations in the neuromuscular system. This article addresses changes in skeletal muscle pathophysiology that occur in patients with heart failure and the potential role resistance training may play in reversing this sequela, and recommends a weight lifting exercise prescription for these patients.

Reduced reactive hyperemia in HIV-infected patients

BACKGROUND

Given that several pathology-based studies reported some degree of coronary and arterial vasculopathy in HIV-infected patients, we investigated whether abnormal vascular reactivity may also be found in these patients.

METHODS

Vascular reactivity was assessed noninvasively using finger-skin blood-flow monitoring by laser-Doppler flow measurement in 10 HIV-infected-patients (mean CD4 T-cell count, 350+/-84 cells/mm3) with cardiac symptoms (previous myocardial infarction or left-ventricular dysfunction) and/or HIV-related protease inhibitor-induced hyperlipemia (group 1, symptomatic), 19 HIV-infected patients free of cardiac disease, hyperlipemia, and previous opportunistic infections (mean CD4 T-cell count, 333+/-175 cells/mm3; group 2, asymptomatic), and 19 healthy control subjects (group 3). Laser-Doppler flow was measured at baseline, during postocclusive hyperemic response following transient interruption of brachial blood flow (reactive hyperemia), during transcutaneous delivery of acetylcholine (Ach) using iontophoresis (endothelium-dependent dilation) and after sublingual nitroglycerin administration (endothelium-independent dilation).

RESULTS

During reactive hyperemia, the absolute increase in flow was found to be lower in asymptomatic HIV-infected patients than in controls (median values [25th-75th percentile]: asymptomatic: 300 [200-400]; versus controls: 600 [400-750] arbitrary units [AU]; p< or =.0001). This abnormality was more pronounced in symptomatic patients (100 [100-200]; p< or =.0001). There was also a reduced peak/baseline flow ratio (symptomatic: 1.14 [1.1-1.2]; asymptomatic: 1.40 [1.25-1.5]; versus controls: 1.83 [1.6-2.2]; p<.0001 for both comparisons) and a reduced hyperemic response, as assessed by the curve of area under the flow versus time from deflation to the end of the hyperemic response (symptomatic: 1850 [1100-2225]; asymptomatic: 6000 [2850-7950]; versus controls: 23,735 [16,000-31, 800] AU x sec; p<.0001 for both comparisons). Although there was no statistically significant difference in acetylcholine (Ach)-induced increases in flow between asymptomatic HIV patients and controls (peak/baseline flow ratio: 6 [4.4-10] versus 5.3 [4-8]; p =.47), a trend to lower values was seen in symptomatic patients (4.4 [1.2-5]; p =.06). Administration of 0.4 mg sublingual nitroglycerin resulted in increases in flow without statistically significant difference between patients and controls: peak/baseline flow ratio for symptomatic: 2.4 [1.9-2.7]; asymptomatic: 2.1 [1.75-2.34] versus controls: 1.97 [1.8-2.4]; p =.2 and.83, respectively).

CONCLUSIONS

Postischemic reactive hyperemia is reduced in HIV-infected patients. In addition, there was is trend for a reduced response to Ach only in those with cardiac disease and/or hyperlipemia.

Adaptive responses of the endothelium to stress

It is now established that endothelial cells acquire several functional properties in response to a diverse array of extracellular stimuli. This expression of an altered phenotype is referred to as endothelial cell activation, and it includes several activities that promote inflammation and coagulation. While it is recognized that endothelial cell activation has a principal role in host defense, recent studies also demonstrate that endothelial cells are capable of complex molecular responses that protect the endothelium against various forms of stress including heat shock, hypoxia, oxidative stress, shock, ischemia-reperfusion injury, toxins, wounds, and mechanical stress. In this review, we examine endothelial cell genotypic and phenotypic responses to stress. Also, we highlight important cellular stress responses that, although not yet demonstrated directly in endothelial cells, likely exist as part of the repertoire of stress responses in endothelium. A detailed understanding of the molecular mechanisms mediating the adaptive responses of endothelial cells to stress should facilitate the development of novel therapeutics to aid in the management of diverse surgical diseases and their complications.

The effect of nitric oxide on ischemia-reperfusion injury in rat liver

A dual role for nitric oxide (NO) in ischemia-reperfusion (I/R) injury is still controversial. This study aims to investigate the role of NO in rat hepatic reperfusion injury. Ischemia was induced by total occlusion of hepatic artery and portal vein for 30 min, then the tissue was reperfused for 30 min. The animals in the L-NAME group (n=10) received N(G)nitro-L-arginine methyl ester (L-NAME) (15 mg/kg) intraperitoneally 60 min before ischemia. The ischemia group (n=10) was given an equal volume of saline solution. The control group comprised eight healthy rats which were not exposed to ischemia or reperfusion. An indicator of hepatic injury, plasma alanine amino transferase (ALT) enzyme activities, were increased in the L-NAME group as compared with the ischemia group (p<0.001). The level of serum nitrite, an index of NO production, and hepatic reduced glutathione (GSH) concentration were lower in the L-NAME group than in the ischemia group (p<0.001, p<0.01, respectively). Hepatic levels of malondialdehyde (MDA) and conjugated dienes (CD) were significantly increased in the L-NAME group as compared to the ischemia group (p<0.05, p<0.001, respectively). Our results confirm that L-NAME, an inhibitor of the enzyme NO synthase, increased the lipid peroxidation and possibly tissue injury, due to the inhibition of cytoprotective effects of NO in a rat hepatic I/R model.

Increased release of nitric oxide in ischemic hearts after exercise in patients with effort angina

OBJECTIVES

The aim of this study was to determine whether the release of nitric oxide (NO) from the ischemic heart increases during exercise in patients with effort angina.

BACKGROUND

Myocardial ischemia increases NO production in the canine heart, but no such increase has been demonstrated in the ischemic human heart.

METHODS

Fifteen patients with effort angina underwent supine ergometer exercise tests. All patients had severe proximal stenosis (>90%) in the left anterior descending coronary artery. The control group consisted of 17 subjects without coronary artery disease or systemic hemodynamic abnormalities.

RESULTS

Neither the lactate extraction ratio (LER) nor the difference in NO concentration between coronary venous and arterial blood (deltaVA[NO]) was affected by exercise in the control subjects. In patients with effort angina, neither variable differed from that in the control group at rest; however, exercise markedly decreased LER and significantly increased deltaVA(NO) (from 4.7 +/- 0.3 to 16.5 +/- 1.6 micromol/liter, p < 0.001) in the patient group. The extent of decrease in LER was significantly correlated with the extent of increase in deltaVA(NO) in the patients with effort angina (r2 = -0.837, p < 0.001).

CONCLUSIONS

Provocation of myocardial ischemia by exercise stress increases NO production in the hearts of patients with effort angina.

Effect of heart transplantation on impaired peripheral microvascular perfusion and reactivity in congestive heart failure

Whether reduced peripheral blood flow in congestive heart failure is reversed after heart transplantation, has not been closely examined. We therefore studied skin microvascular resting perfusion and reactivity in patients pre- and postoperatively. Resting digital skin perfusion, together with the responses to cold pressor test, postocclusive reactive hyperemia and direct skin heating were examined with laser Doppler perfusion measurements. We examined 28 patients with congestive heart failure and 14 of these patients after heart transplantation and compared them to 13 healthy controls. Measurements were performed within 3 months preoperatively and 12 days, 1, 2, 3 and 6 months postoperatively. Patients with congestive heart failure had significantly lower resting perfusion levels than controls and demonstrated attenuated responses to both stimuli of vasodilation (all P<0.01). While peak hyperemic responses improved significantly after transplantation, postocclusive area under the hyperemic curve decreased further, and none of these variables were normalized after 6 months. In contrast, minimal perfusion during cold pressor test increased from a significantly lower level in the patients with congestive heart failure (P<0.05), to a level similar to that of the controls within 12 days postoperatively. Thus, skin microvascular perfusion and reactivity improve, but are not normalized within 6 months of transplantation. Both pre- and postoperative factors may be involved in maintaining a dysfunction of the peripheral microcirculation, which may contribute to exercise intolerance and hypertension in heart transplant recipients.

Explaining fatigue in congestive heart failure

Fatigue is a prominent symptom in patients with chronic heart failure, limiting physical activity and impairing quality of life. Although the underlying mechanisms are not clearly identified, alterations associated with peripheral adaptation in heart failure appear to play an important role, including a variably impaired peripheral perfusion during exercise, reduced oxidative capacity of skeletal muscle, impaired muscle strength, and possibly reflex mechanisms associated with alterations in the metabolism of skeletal muscle. Exercise training can, in part, reverse these peripheral alterations, improve exercise capacity, and alleviate fatigue.