Vascular compliance versus flow-mediated vasodilation: correlation with cardiovascular risk factors

The Multiscale Dynamics of Beat-to-Beat Blood Pressure Fluctuation Links to Functions in Older Adults

Background

The blood pressure (BP) is regulated by multiple neurophysiologic elements over multiple temporal scales. The multiscale dynamics of continuous beat-to-beat BP series, which can be characterized by “BP complexity”, may, thus, capture the subtle changes of those elements, and be associated with the level of functional status in older adults. We aimed to characterize the relationships between BP complexity and several important functions in older adults and to understand the underlying factors contributing to BP complexity.

Method

A total of 400 older adults completed a series of clinical and functional assessments, a finger BP assessment of at least 10 min, and blood sample and vessel function tests. Their hypertensive characteristics, cognitive function, mobility, functional independence, blood composition, arterial stiffness, and endothelial function were assessed. The complexity of systolic (SBP) and diastolic (DBP) BP series was measured using multiscale entropy.

Results

We observed that lower SBP and DBP complexity was significantly associated with poorer functional independence (β > 0.17, p < 0.005), cognitive function (β > 0.45, p = 0.01), and diminished mobility (β < −0.57, p < 0.003). Greater arterial stiffness (β < −0.48, p = 0.02), decreased endothelial function (β > 0.42, p < 0.03), and excessed level of blood lipids (p < 0.03) were the main contributors to BP complexity.

Conclusion

Blood pressure complexity is closely associated with the level of multiple functional statuses and cardiovascular health in older adults with and without hypertension, providing novel insights into the physiology underlying BP regulation. The findings suggest that this BP complexity metric would serve as a novel marker to help characterize and manage the functionalities in older adults.

Predictors of Calf Arterial Compliance in Male Veterans With Psychiatric Diagnoses

BACKGROUND

Peripheral arterial compliance (PAC) is a measure of the ability of the vascular tree to dilate in response to a pressure wave. Reduced PAC is seen in patients with psychiatric diagnoses and has been associated with increased risk for stroke, myocardial infarction, and mortality. The objective of this pilot study was to identify predictors of reduced PAC in subjects with psychiatric diagnoses.

METHODS

Male psychiatric subjects (N = 77) were studied in a cross-sectional study of medication effects on PAC conducted from August 2005 to February 2010. Calf and thigh compliance were modeled in separate linear regressions. The models were adjusted for age, race, smoking status, presence or absence of the metabolic syndrome, current treatment with a statin, diagnosis of schizophrenia or schizoaffective disorder, current antipsychotic treatment, and body mass index (BMI).

RESULTS

Of the 77 subjects (mean ± SD age of 53.7 ± 8.8 years), 41 were white, 36 were black, and 27 were diagnosed with schizophrenia or schizoaffective disorder (DSM-IV criteria). Fifty participants were being treated with an antipsychotic medication, while the remaining 27 were off of antipsychotics for at least 2 months. Our model explained 27% of the variance in calf compliance. Black subjects had reduced calf compliance compared to white subjects (P = .02). Having metabolic syndrome was associated with reduced PAC at a trend level (P < .08), and BMI (P = .004) and BMI² (P = .011) were significant predictors of calf compliance. Schizophrenia versus other psychiatric diagnoses and antipsychotic treatment were not significantly associated with calf compliance.

CONCLUSIONS

In this pilot study, significant predictors of calf compliance were race (black vs white) and BMI. PAC is a noninvasive measure that may be a predictor of cardiovascular risk in psychiatric patients. The reduced PAC seen in patients with psychiatric diagnoses does not appear to be directly related to their diagnosis or antipsychotic treatment but rather to other characteristics inherent to the subject. Future studies are warranted to better understand the pathophysiology of PAC including but not limited to inflammation in psychiatric patients.

Modulating the vascular response to limb ischemia: angiogenic and cell therapies

The age-adjusted prevalence of peripheral arterial disease in the US population has been estimated to approach 12%. The clinical consequences of occlusive peripheral arterial disease include pain on walking (claudication), pain at rest, and loss of tissue integrity in the distal limbs; the latter may ultimately lead to amputation of a portion of the lower extremity. Surgical bypass techniques and percutaneous catheter-based interventions may successfully reperfuse the limbs of certain patients with peripheral arterial disease. In many patients, however, the anatomic extent and distribution of arterial occlusion is too severe to permit relief of pain and healing of ischemic ulcers. No effective medical therapy is available for the treatment of such patients, for many of whom amputation represents the only hope for alleviation of symptoms. The ultimate failure of medical treatment and procedural revascularization in significant numbers of patients has led to attempts to develop alternative therapies for ischemic disease. These strategies include administration of angiogenic cytokines, either as recombinant protein or as gene therapy, and more recently, to investigations of stem/progenitor cell therapy. The purpose of this review is to provide an outline of the preclinical basis for angiogenic and stem cell therapies, review the clinical research that has been done, summarize the lessons learned, identify gaps in knowledge, and suggest a course toward successfully addressing an unmet medical need in a large and growing patient population.

Associations of noninvasive measures of arterial compliance and ankle-brachial index: the Multi-Ethnic Study of Atherosclerosis (MESA)

BACKGROUND

The association between measures of arterial compliance and peripheral arterial disease (PAD) is unclear. Early changes in arterial wall compliance could be a useful marker of patients at high risk for developing lower extremity atherosclerosis.

METHODS

We used linear and logistic regression models on baseline data from 2,803 female and 2,558 male participants in the Multi-Ethnic Study of Atherosclerosis (MESA) to study associations between tonometry-derived baseline measures of arterial compliance (large artery compliance (C1) and small artery compliance (C2)) and the baseline ankle-brachial index (ABI), as well as change in the ABI over ~3 years of follow-up.

RESULTS

In cross-sectional analyses, lower C1 and C2 values, indicating poorer arterial compliance, were associated with lower ABI. There were significant linear trends across strata of ABI, especially in C2 which ranged from 3.7 ml/mm Hg × 100 (95% confidence interval (CI) 3.3-4.2) in women with an ABI < 0.90 to 4.2 ml/mm Hg × 100 (95% CI 4.1-4.3 P < 0.001) in women with ABI 1.10 - <1.40. Similar significant trends (P < 0.001) were seen in men. In prospective analyses, those with the lowest tertile of C2 values at baseline had a greater multivariable-adjusted odds for decline in ABI of ≥ 0.15 over 3 years compared to those with the highest C2 values at baseline (odds ratio (OR) 1.80, 95% CI 1.23-2.64).

CONCLUSIONS

We observed that less compliant arteries were significantly associated with low ABI in cross-sectional analysis and with greater decline in odds of ABI over time.

Basal and post-ischemic vascular compliance in children/adolescents born small for gestational age

BACKGROUND

Intrauterine growth restriction plays a powerful role in influencing later susceptibility to certain chronic diseases, such as hypertension. Endothelial dysfunction and arterial stiffness are early events in the development of cardiovascular diseases (CVDs). We have studied vascular compliance in small for gestational age (SGA) children/adolescents in comparison with that in appropriate for gestational age (AGA) subjects.

METHODS

We monitored blood pressure, vascular resistance and compliance in 82 children-adolescents (52 SGA, 30 AGA), by means of pulse wave analysis (CR 2000 HDI) at the radial level, before and after 3 min of ischemic stress at the brachial level.

RESULTS

In the children/adolescents born SGA we found a significant increase in systolic and diastolic blood pressure and vascular resistance in the basal condition; the large and small vessels were stiffer. After ischemia we observed an increased vascular response in the SGA children/adolescents: there was a great diminution of systolic and diastolic blood pressure and a larger increase of the elasticity of the conduit and resistance vessels.

CONCLUSIONS

These data show that the SGA group presented some early signs of arterial wall functional disorders. More pediatric data are needed for the evaluation by non-invasive techniques of vascular function in children-adolescents at risk of CVD.

Inhibition of iNOS protects endothelial-dependent vasodilation in aged rats

AIM

To examine whether iNOS contributes to endothelial dysfunction in aged rats.

METHODS

Male Sprague Dawley rats were divided into three groups: young rats, aged rats treated with vehicle and aged rats treated with N-[3-(Aminomethyl) benzyl] acetamidine (1400W, 1 mg/kg, ip). Vasorelaxation was measured in isolated thoracic aorta. iNOS expression of thoracic aortic arteries was detected using immunohistochemistry and Western blot. Nitrotyrosine (a marker for peroxynitrite formation) content and expression in thoracic aortic tissue were determined using enzyme linked immunosorbent assay and immunohistochemistry.

RESULTS

Maximal relaxation induced by acetylcholine (10⁻⁹ to 10⁻⁵ mol/L) in the aged rats treated with vehicle was significantly decreased (70%±15%, P<0.01), as compared with the young rats (95%±8%). However, the maximal relaxation induced by acidified NaNO2 (an endothelium-independent vasodilator) had no significant difference between the two groups. Moreover, iNOS and nitrotyrosine expression increased in the vessels of the aged rats. In the aged rats treated with 1400W (a highly selective iNOS inhibitor) nitrotyrosine expression was reduced and acetylcholine-induced vasorelaxation was markedly improved (maximal relaxation was increased to 87%±8%, P<0.05), but the acidified NaNO₂-induced vasorelaxation had no significant change.

CONCLUSION

Our study demonstrated that inhibition of iNOS by 1400W increased endothelium-dependent vasodilation in aged rats. The mechanism was related with attenuation of peroxynitrite formation.

The endothelial cell in health and disease: its function, dysfunction, measurement and therapy

Endothelial cells have numerous endocrine functions and contribute to a variety of processes, including penile erection and vasodilation. Endothelial dysfunction is associated with cardiovascular risk factors and has been implicated in the pathogenesis of atherosclerosis and ED. This study reviews endothelial function, in addition to endothelial dysfunction and its role in atherosclerosis and ED. Measurement of endothelial function is reviewed, including catheter-based methods, venous occlusion plethysmography, high-frequency ultrasound, peripheral arterial tonometry, digital pulse amplitude tonometry, digital thermal monitoring, the L-arginine test and measurement of compounds released by endothelial cells. Therapy and medications that improve endothelial function are reviewed. As the scientific community learns more about the importance of the endothelium, it is increasingly important for the clinician to understand endothelial function, dysfunction, measurement of endothelial function and therapies that affect this remarkable cell type.

Untreated HIV infection and large and small artery elasticity

BACKGROUND

Untreated HIV infection may increase risk for cardiovascular disease, and arterial elasticity is a marker of cardiovascular risk and early disease.

METHODS

HIV-infected participants not taking antiretroviral therapy (n=32) were compared with HIV-negative controls (n=30). Large and small artery elasticity (LAE and SAE) were estimated via analysis of radial pulse waveforms. Differences in LAE and SAE by HIV status were compared using analysis of covariance, with and without adjustment for Framingham risk (model 1); covariates that differed between groups [smoking, injection drug use, hepatitis C, and high-density lipoprotein cholesterol (HDLc); model 2]; or age, sex, race/ethnicity, smoking, injection frug use, hepatitis C, HDLc, and non-HDLc (model 3).

RESULTS

HIV infection was associated with impaired LAE (-2.55 mL/mm Hg x 10; P=0.02) and SAE (-1.50 mL/mm Hg x 100; P=0.02). Associations with traditional risk factors were often stronger for SAE than LAE, including with Framingham score (per 1% higher; SAE -0.18, P=0.01; LAE -0.19, P=0.13). Fasting lipid levels were not significantly associated with LAE and SAE. After adjustment, differences between HIV-infected and HIV-uninfected participants were similar in model 1 (-2.36 for LAE, P=0.04; -1.31 for SAE, P=0.04), model 2 (-2.67 for LAE, P=0.02; -1.13 for SAE, P=0.07) and model 3 (-2.91 for LAE, P=0.02; -1.34 for SAE, P=0.03). CD4 count and HIV RNA level were not associated with LAE and SAE among HIV-infected participants.

CONCLUSIONS

Untreated HIV infection is associated with impaired arterial elasticity, of both the large and small vasculature, after controlling for additional risk factors. Pulse waveform analysis is a noninvasive technique to assess cardiovascular disease risk that should be evaluated in larger studies of HIV-infected persons.

l -Arginine Supplementation in Peripheral Arterial Disease

Background— l -Arginine is the precursor of endothelium-derived nitric oxide, an endogenous vasodilator. l -Arginine supplementation improves vascular reactivity and functional capacity in peripheral arterial disease (PAD) in small, short-term studies. We aimed to determine the effects of long-term administration of l -arginine on vascular reactivity and functional capacity in patients with PAD.

Methods and Results— The Nitric Oxide in Peripheral Arterial Insufficiency (NO-PAIN) study was a randomized clinical trial of oral l -arginine (3 g/d) versus placebo for 6 months in 133 subjects with intermittent claudication due to PAD in a single-center setting. The primary end point was the change at 6 months in the absolute claudication distance as assessed by the Skinner-Gardner treadmill protocol. l -Arginine supplementation significantly increased plasma l -arginine levels. However, measures of nitric oxide availability (including flow-mediated vasodilation, vascular compliance, plasma and urinary nitrogen oxides, and plasma citrulline formation) were reduced or not improved compared with placebo. Although absolute claudication distance improved in both l -arginine- and placebo-treated patients, the improvement in the l -arginine-treated group was significantly less than that in the placebo group (28.3% versus 11.5%; P =0.024).

Conclusions— In patients with PAD, long-term administration of l -arginine does not increase nitric oxide synthesis or improve vascular reactivity. Furthermore, the expected placebo effect observed in studies of functional capacity was attenuated in the l -arginine-treated group. As opposed to its short-term administration, long-term administration of l -arginine is not useful in patients with intermittent claudication and PAD.