New methods for arterial diameter measurement from B-mode images

Effects of Different Eccentric Cycling Intensities on Brachial Artery Endothelial Shear Stress and Blood Flow Patterns

Eccentric exercise has gained attention as a novel exercise modality that increases muscle performance at a lower metabolic demand. However, vascular responses to eccentric cycling (ECC) are unknown, thus gaining knowledge regarding endothelial shear stress (ESS) during ECC may be crucial for its application in patients. The purpose of this study was to explore ECC-induced blood flow patterns and ESS across three different intensities in ECC. Eighteen young, apparently healthy subjects were recruited for two laboratory visits. Maximum oxygen consumption, power output, and blood lactate (BLa) threshold were measured to determine workload intensities. Blood flow patterns in the brachial artery were measured via ultrasound imaging and Doppler on an eccentric ergometer during a 5 min workload steady exercise test at low (BLa of 0-2 mmol/L), moderate (BLa 2-4 mmol/L), and high intensity (BLa levels > 4 mmol/L). There was a significant increase in the antegrade ESS in an intensity-dependent manner (baseline: 44.2 ± 8.97; low: 55.6 ± 15.2; moderate: 56.0 ± 10.5; high: 70.7 ± 14.9, all dynes/cm2, all p values < 0.0002) with the exception between low and moderate and Re (AU) showed turbulent flow at all intensities. Regarding retrograde flow, ESS also increased in an intensity-dependent manner (baseline 9.72 ± 4.38; low: 12.5 ± 3.93; moderate: 15.8 ± 5.45; high: 15.7 ± 6.55, all dynes/cm2, all p values < 0.015) with the exception between high and moderate and Re (AU) showed laminar flow in all intensities. ECC produced exercise-induced blood flow patterns that are intensity-dependent. This suggests that ECC could be beneficial as a modulator of endothelial homeostasis.

Theoretical and Experimental Study on Assessment of Flow-Mediated Dilatation Using the Cuff Method in Brachial Arteries

Endothelial dysfunction has been shown to be an important risk factor in the pathogenesis of atherosclerosis, hypertension, and heart failure. The flow-mediated vasodilation (FMD) of the peripheral arteries is an endothelium-dependent function, which is assessed by measuring the diameter change in the brachial artery before and after ischemic stress. Brachial-artery ultrasound scanning (BAUS) is the gold standard for assessing the FMD in clinical practice. However, ultrasonography requires an operator or physician with a professional training to perform accurate measurement of the diameter of the brachial artery. Thus, some studies have used the cuff method to measure the FMD in percentage, the value of which is significantly larger than that using BAUS. The goal of this study was to explore this phenomenon. We explain the interaction between the volume changes (oscillation magnitudes in volume due to cardiac pulsations) of the artery and cuff bladder under different transmural pressures when a sphygmomanometer is wrapped around an upper arm. The compliance of the cuff bladder would be of a fixed value when the cuff pressure is low. The cuff-volume change could be replaced with a cuff-pressure change (oscillation magnitude in cuff pressure due to cardiac pulsation). With the cuff method, the FMDc could be assessed with pressure changes. Then, an inequality formula regarding FMD values by both BAUS (FMDu) and the cuff method (FMDc) was derived; FMDc > 2*FMDu + FMDu2. In order to experimentally verify this inequality formula, fifty-one subjects, including thirty-eight healthy adults and thirteen patients with hypertension, participated in this study. The systolic and diastolic diameters of their brachial arteries and cuff-pressure changes due to cardiac pulsations were separately measured by BAUS and a pressure sensor before and after an ischemic stress. The results showed that FMDu and FMDc were 8.1 ± 4.3% and 121.6 ± 48.6% in the healthy group and 4.5 ± 1.1% and 55.2 ± 22.8% in the patient group, respectively. Thus, the experimental findings comply with the theoretically derived inequality formula.

Impact of Acipimox Therapy on Free Fatty Acid Efflux and Endothelial Function in the Metabolic Syndrome: A Randomized Trial

OBJECTIVE

Insulin resistance is associated with increased lipolysis and elevated concentrations of free fatty acids (FFA), which in turn contribute to impaired vascular function. It was hypothesized that lowering FFA with acipimox, a nicotinic acid derivative that impairs FFA efflux, would improve endothelial function, measured by flow-mediated dilation (FMD), in individuals with metabolic syndrome.

METHODS

A total of 18 participants with metabolic syndrome and 17 healthy controls were enrolled and treated with acipimox 250 mg orally every 6 hours or placebo for 7 days in a randomized, double-blind, crossover trial.

RESULTS

Acipimox reduced FFA concentrations among individuals with metabolic syndrome to near normal levels (P = 0.01), but there was no change among healthy controls (P = 0.17). Acipimox did not improve endothelial-dependent FMD in either group (metabolic syndrome: P = 0.42; healthy controls: P = 0.16), although endothelial-independent nitroglycerin-mediated dilation among those with metabolic syndrome tended to increase (20.3%, P = 0.06). There were no changes in blood lipids or markers of inflammation following therapy. There was minimal correlation between change in FMD and baseline measures of BMI ( ρ = -0.09) or waist circumference ( ρ = -0.15).

CONCLUSIONS

In groups with normal or elevated baseline FFA, short-term reductions do not improve endothelial function assessed by FMD.

Intra- and inter-operator reproducibility of automated cloud-based carotid lumen diameter ultrasound measurement

BACKGROUND

Common carotid artery lumen diameter (LD) ultrasound measurement systems are either manual or semi-automated and lack reproducibility and variability studies. This pilot study presents an automated and cloud-based LD measurements software system (AtheroCloud) and evaluates its: (i) intra/inter-operator reproducibility and (ii) intra/inter-observer variability.

METHODS

100 patients (83M, mean age: 68±11years), IRB approved, consisted of L/R CCA artery (200 ultrasound images), acquired using a 7.5-MHz linear transducer. The intra/inter-operator reproducibility was verified using three operator's readings. Near-wall and far carotid wall borders were manually traced by two observers for intra/inter-observer variability analysis.

RESULTS

The mean coefficient of correlation (CC) for intra- and inter-operator reproducibility between all the three automated reading pairs were: 0.99 (P<0.0001) and 0.97 (P<0.0001), respectively. The mean CC for intra- and inter-observer variability between both the manual reading pairs were 0.98 (P<0.0001) and 0.98 (P<0.0001), respectively. The Figure-of-Merit between the mean of the three automated readings against the four manuals were 98.32%, 99.50%, 98.94% and 98.49%, respectively.

CONCLUSIONS

The AtheroCloud LD measurement system showed high intra/inter-operator reproducibility hence can be adapted for vascular screening mode or pharmaceutical clinical trial mode.

Assessment of the endothelial function with changed volume of brachial artery by menstrual cycle

BACKGROUND

The endothelial function has been proven to be an important factor in the pathogenesis of atherosclerosis, hypertension and heart failure. The flow-mediated vasodilation (FMD) of the peripheral artery is an endothelium-dependent function. Brachial-artery ultrasound scanning is the popular method for evaluating FMD. However, good technical training on ultrasonography is required for the user to obtain high-quality data. Therefore, the goal of this study was to propose a new method which only used a sphygmomanometer cuff to occlude the blood flow and record the vascular volume waveform (Vwave).

RESULTS

We used this method to assess the FMD in the menstrual cycle for 26 volunteer females. All female subjects were evaluated two times (M: menstrual phase; F: luteal phase) in one menstrual cycle and for two cycles. In the first cycle, the FMD volume ratio in M was 101.9 ± 45.5 % and was higher in L, at 137.5 ± 62.1 % (p = 0.0032 versus M). In the second cycle, the FMD volume ratios in M and L were 91.4 ± 37.0 % and 124.0 ± 56.4 %, respectively (p < 0.001 vs. M).

CONCLUSIONS

Our results have confirmed those results in the study of Hametner et al. Blood pressure measurement and FMD assessment all used the same mechanic of digital blood pressure monitor, which makes our method suitable using at home.

FloWave.US: validated, open-source, and flexible software for ultrasound blood flow analysis

Automated software improves the accuracy and reliability of blood velocity, vessel diameter, blood flow, and shear rate ultrasound measurements, but existing software offers limited flexibility to customize and validate analyses. We developed FloWave.US-open-source software to automate ultrasound blood flow analysis-and demonstrated the validity of its blood velocity (aggregate relative error, 4.32%) and vessel diameter (0.31%) measures with a skeletal muscle ultrasound flow phantom. Compared with a commercial, manual analysis software program, FloWave.US produced equivalent in vivo cardiac cycle time-averaged mean (TAMean) velocities at rest and following a 10-s muscle contraction (mean bias <1 pixel for both conditions). Automated analysis of ultrasound blood flow data was 9.8 times faster than the manual method. Finally, a case study of a lower extremity muscle contraction experiment highlighted the ability of FloWave.US to measure small fluctuations in TAMean velocity, vessel diameter, and mean blood flow at specific time points in the cardiac cycle. In summary, the collective features of our newly designed software-accuracy, reliability, reduced processing time, cost-effectiveness, and flexibility-offer advantages over existing proprietary options. Further, public distribution of FloWave.US allows researchers to easily access and customize code to adapt ultrasound blood flow analysis to a variety of vascular physiology applications.

American Society of Echocardiography Report

Noninvasive measures of atherosclerosis have emerged as adjuncts to standard cardiovascular disease (CVD) risk factors in an attempt to refine risk stratification and the need for more aggressive preventive strategies. Two such approaches, carotid artery imaging and brachial artery reactivity testing (BART), are ultrasound based. Numerous carotid artery imaging protocols have been used, and methodologic aspects are described in detail in this review. The panel recommends that protocols: (1) use end-diastolic (minimum dimension) images for intimal-medial thickness (IMT) measurements; (2) provide separate categorization of plaque presence and IMT; (3) avoid use of a single upper limit of normal for IMT because the measure varies with age, sex, and race; and (4) incorporate lumen measurement, particularly when serial measurements are performed to account for changes in distending pressure. Protocols may vary in the number of segments wherein IMT is measured, whether near wall is measured in addition to far wall, and whether IMT measurements are derived from B-mode or M-mode images, depending on the application. BART is a technique that requires meticulous attention to patient preparation and methodologic detail. Its application is substantially more challenging than is carotid imaging and remains largely a research technique that is not readily translated into routine clinical practice.

Accuracy and robustness of a simple algorithm to measure vessel diameter from B-mode ultrasound images

Measurement of changes in arterial vessel diameter can be used to assess the state of cardiovascular health, but the use of such measurements as biomarkers is contingent upon the accuracy and robustness of the measurement. This work presents a simple algorithm for measuring diameter from B-mode images derived from vascular ultrasound. The algorithm is based upon Gaussian curve fitting and a Viterbi search process. We assessed the accuracy of the algorithm by measuring the diameter of a digital reference object (DRO) and ultrasound-derived images of a carotid artery. We also assessed the robustness of the algorithm by manipulating the quality of the image. Across a broad range of signal-to-noise ratio and with varying image edge error, the algorithm measured vessel diameter within 0.7% of the creation dimensions of the DRO. This was a similar level of difference (0.8%) to when an ultrasound image was used. When SNR dropped to 18 dB, measurement error increased to 1.3%. When edge position was varied by as much as 10%, measurement error was well maintained between 0.68 and 0.75%. All these errors fall well within the margin of error established by the medical physics community for quantitative ultrasound measurements. We conclude that this simple algorithm provides consistent and accurate measurement of lumen diameter from B-mode images across a broad range of image quality.

Automatic Measurement of End-Diastolic Arterial Lumen Diameter in ARTSENS

Over past few years, we are developing a system for facilitating large scale screening of patients for cardiovascular risk—arterial stiffness evaluation for noninvasive screening (ARTSENS). ARTSENS is an image-free device that uses a single element ultrasound transducer to obtain noninvasive measurements of arterial stiffness (AS) in a fully automated manner. AS is directly proportional to end-diastolic lumen diameter (Dd). Multilayered structure of the arterial walls and indistinct characteristics of intima-lumen interface (ILI) makes it quite difficult to accurately estimate Dd in A-mode radio-frequency (RF) frames obtained from ARTSENS. In this paper, we propose a few methods based on fitting simple mathematical models to the echoes from arterial walls, followed by a novel method to fuse the information from curve fitting error and distension curve to arrive at an accurate measure of Dd. To bring down the curve fitting time and facilitate processing on low-end processors, a novel approach using the autocorrelation of echoes from opposite walls of the artery has been discussed. The methods were analyzed for their comparative accuracy against reference Dd obtained from 85 human volunteers using Hitachi-Aloka eTRACKING system. Dd from all reported methods show strong and statistically significant positive correlation with eTRACKING and mean error of less than 7% could be achieved. As expected, Dd from all methods show significant positive correlation with age.

Cardiac output, blood pressure variability, and cognitive decline in geriatric cardiac patients

OBJECTIVE

To prospectively investigate whether baseline findings on specific cardiovascular indices are predictive of subsequent rate of decline in Attention-Executive-Psychomotor function in a cohort of ambulatory older adults with cardiovascular diseases (CVDs).

METHODS

One hundred seventy-two older adults with CVD were administered a neuropsychological battery of executive functions tests at study entry, and at 12 and 36 months thereafter. At study entry, they also underwent vascular assessments including cardiac output, ejection fraction, blood pressure (BP), brachial artery reactivity, and carotid intima media thickness. Random coefficient regressions were used to investigate the effect of these cardiac indices on rate of decline in Attention-Executive-Psychomotor function.

RESULTS

Cardiac output, systolic BP variability, and diastolic BP variability predicted decline in Attention-Executive-Psychomotor function. Specifically, lower cardiac output, reduced variability in systolic BP, and increased variability in diastolic BP were associated with a faster rate of decline in Attention-Executive-Psychomotor function. Mean resting systolic and diastolic blood pressure did not predict decline in Attention-Executive-Psychomotor function.

CONCLUSIONS

Decline in frontal-subcortical cognitive functions among patients with CVDs appears to be mediated by systemic hypoperfusion and variability in blood pressure. The precise nature of these relationships, especially with regard to blood pressure variability, is complex and demands continued investigation.

Medical ultrasound: imaging of soft tissue strain and elasticity

After X-radiography, ultrasound is now the most common of all the medical imaging technologies. For millennia, manual palpation has been used to assist in diagnosis, but it is subjective and restricted to larger and more superficial structures. Following an introduction to the subject of elasticity, the elasticity of biological soft tissues is discussed and published data are presented. The basic physical principles of pulse-echo and Doppler ultrasonic techniques are explained. The history of ultrasonic imaging of soft tissue strain and elasticity is summarized, together with a brief critique of previously published reviews. The relevant techniques-low-frequency vibration, step, freehand and physiological displacement, and radiation force (displacement, impulse, shear wave and acoustic emission)-are described. Tissue-mimicking materials are indispensible for the assessment of these techniques and their characteristics are reported. Emerging clinical applications in breast disease, cardiology, dermatology, gastroenterology, gynaecology, minimally invasive surgery, musculoskeletal studies, radiotherapy, tissue engineering, urology and vascular disease are critically discussed. It is concluded that ultrasonic imaging of soft tissue strain and elasticity is now sufficiently well developed to have clinical utility. The potential for further research is examined and it is anticipated that the technology will become a powerful mainstream investigative tool.

Effects of carbenoxolone on flow-mediated vasodilatation in healthy adults

Gap junctions play a key role in maintaining the functional integrity of the vascular wall. Using carbenoxolone (CBX) as a gap junction blocker, we aimed to assess the contribution of gap junctions in the vascular wall to flow-mediated vasodilatation (FMD) in healthy adults. Percentage FMD (%FMD) and circulating vasoactive molecules/activity, including atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP), aldosterone, cortisol, plasma renin activity (PRA), and endothelin (ET-1), were measured in 25 healthy volunteers (mean age: 30.1 ± 5.4 yr; 14 males) before and after oral administration of CBX (100 mg). %FMD decreased after ingestion of CBX (9.71 ± 3.1 vs. 3.40 ± 2.0%; P < 0.0001). The levels of ANP, BNP, cortisol, and ET-1 remained stationary, while both PRA and aldosterone decreased ( P < 0.005) after CBX ingestion. Blood pressure and heart rate were minimally changed by CBX. Inhibition of gap junctional communication by CBX impairs FMD in healthy persons, suggesting that physiologically, vascular gap junctions participate in the maintenance of FMD. CBX does not induce the release of vasoconstricting molecules or enhance vasoconstriction, suggesting that inhibition of gap junctional communication by CBX underlies the impairment of FMD. Therefore, administering CBX in FMD examination can be a way to follow the effect of gap junctions on endothelial function, but further work remains to verify the specificity of CBX effect.

Automatic localization of intimal and adventitial carotid artery layers with noninvasive ultrasound: a novel algorithm providing scan quality control

Transcutaneous ultrasound measurements of common carotid artery (CCA) diameter and intima-media thickness (IMT) give insight on arterial dynamics and anatomy, both correlating well with atherosclerosis and risk of cardiovascular disease. We propose a novel automatic algorithm to estimate CCA diameter and IMT in ultrasound (US) images, based on separate analysis of anterior and posterior CCA walls and able to distinguish internal (intima-intima) and external (adventitia-adventitia) diameter. The method combines off-line signal- and image-processing techniques to accommodate echo images acquired at a frame rate of 30 Hz and composed directly from RF data, circumventing digital video-grabbing. Segmentation consists of automatic CCA recognition, followed by adventitial delineation performed with a sustain-attack filter with exponentially decaying reference functions. Intimal delineation is then based on the multiscale anisotropic barycenter (MAB), which is an extension of a known delineation method involving the "first order absolute central moment" of the echo amplitude. An automatic measure of the quality of the US beam incidence for each wall is superimosed on the CCA contour overlays for visual feedback. Validation is carried out on 36 US CCA acquisitions from 12 healthy volunteers, as well as on synthetic US images. Results indicate good accuracy on synthetic US images (within 1.3% for diameter and 3% for IMT). The in vivo intra-recording beat-to-beat variations are on average lower than 50 microm for external diameter and IMT, and lower than 100 microm for internal diameter. A comparison with a commercial device (ART.LAB system) shows that the proposed algorithm performs better in terms of inter-recording precision. The beam incidence control significantly improves the repeatability of IMT estimates, and motivates sonographers actively to maintain a proper scan plane throughout the acquisition to minimize the incidence of confounding factors. The method is clinically viable, providing robust estimates of CCA internal and external diameter and IMT waveforms for both CCA walls, even at a low B-mode update rate of 30 Hz.

Association of abacavir and impaired endothelial function in treated and suppressed HIV-infected patients

BACKGROUND

HIV-infected patients have accelerated atherosclerosis. Abacavir has been associated with increased risk of cardiovascular events, for reasons that remain to be elucidated. As endothelial dysfunction is central to the pathogenesis of atherosclerosis, we tested the hypothesis that current treatment with abacavir is associated with impaired endothelial function.

METHODS

We studied a cohort of 61 antiretroviral-treated patients who had undetectable plasma HIV RNA levels. Endothelial function was assessed by measuring flow-mediated dilation (FMD) of the brachial artery. We compared FMD in patients treated with or without abacavir, while adjusting for traditional risk factors and HIV-specific characteristics.

RESULTS

The median age was 50 years (interquartile range 45-57). The median duration of HIV infection was 18 years, and the median CD4 cell count was 369 cells/microl. Thirty patients (49%) were receiving abacavir. Overall, the median FMD in the HIV-infected patients was low (3.5%; interquartile range 2.3-5.6%). The FMD was lower in the abacavir-treated patients than those not on abacavir (2.8 vs. 4.9%, P = 0.01). After adjustment for traditional risk factors, HIV-specific factors, and baseline brachial artery diameter, current abacavir use was independently associated with lower FMD (P = 0.017). Duration of therapy and CD4 cell count were not associated with reduced FMD.

CONCLUSION

Endothelial function, a central mechanism in atherosclerosis and a marker of cardiovascular risk, is impaired among antiretroviral-treated patients with undetectable viral loads. Current use of abacavir was independently associated with impaired endothelial function. This finding suggests that abnormal endothelial function may underlie the clinically observed increased risk in myocardial infarction among abacavir-treated patients.

Noninvasive assessment of subclinical atherosclerosis in children and adolescents: recommendations for standard assessment for clinical research: a scientific statement from the American Heart Association

Deterioration in endothelial function and arterial stiffness are early events in the development of cardiovascular diseases. In adults, noninvasive measures of atherosclerosis have become established as valid and reliable tools for refining cardiovascular risk to target individuals who need early intervention. With limited pediatric data, the use of these techniques in children and adolescents largely has been reserved for research purposes. Therefore, this scientific statement was written to (1) review the current literature on the noninvasive assessment of atherosclerosis in children and adolescents, (2) make recommendations for the standardization of these tools for research, and (3) stimulate further research with a goal of developing valid and reliable techniques with normative data for noninvasive clinical evaluation of atherosclerosis in pediatric patients. Precise and reliable noninvasive tests for atherosclerosis in youth will improve our ability to estimate future risk for heart attack and stroke. Currently, large longitudinal studies of cardiovascular risk factors in youth, such as the Bogalusa and Muscatine studies, lack sufficient adult subjects experiencing hard outcomes, such as heart attack and stroke, to produce meaningful risk scores like those developed from Framingham data.

Vascular and cognitive functions associated with cardiovascular disease in the elderly

This study examines the relationship between systemic vascular function, neurocognitive performance, and structural brain abnormalities on magnetic resonance imaging (MRI) among geriatric outpatients with treated, stable cardiovascular disease and no history of neurological illness (n = 88, ages 56-85 years). Vascular function was assessed by cardiac ejection fraction and output, sequential systolic and diastolic blood pressures, flow mediated brachial artery reactivity (BAR), and carotid intima media thickness (IMT). White matter hyperintensities (WMH) on MRI were quantified and examined relative to cognitive and vascular function. Principal component analysis revealed two primary vascular components: one associated with cardiac function, the other with atherosclerotic burden/endothelial dysfunction. Both factors were significantly associated with cognitive function and WMH volume. Reduced systolic variability and increased IMT were most strongly related to reduced attention, executive function, and information-processing speed. These findings suggest the possibility that systemic vascular indices may provide proxy measures of cerebrovascular dysfunction and reinforce the importance of achieving greater understanding of interaction between systemic vascular disease and brain dysfunction among elderly people with cardiovascular disease.

Stress responses and baroreflex function in coronary disease

Exaggerated pressor responses to mental stress in patients with coronary artery disease (CAD) are associated with increased risk for subsequent cardiovascular events. The integrated baroreflex gain and its mechanical and neural component were estimated and then related to the blood pressure and heart rate responses to simulated real-life stressors: mental arithmetic and public speaking. Eighteen healthy individuals (aged 61 +/- 8 yr) and 29 individuals with documented CAD but no other comorbidities (aged 59 +/- 8 yr) were studied. Heart rate and blood pressures were continuously assessed before, during preparation for, and during performance of a math task and a speech task. The assessment of beat-to-beat carotid diameters during baroreflex engagement was used to estimate the integrated baroreflex gain and its mechanical and neural component. The CAD subjects demonstrated significantly greater increases in heart rate and blood pressures for the performance of the speech task. However, there were no group differences in integrated cardiovagal baroreflex gain or either mechanical or neural baroreflex component. These findings indicate that the augmented pressor responses in CAD do not result from a generalized arterial baroreflex deficit.

A novel method to estimate the aortic pressure waveform using B-mode ultrasound images acquired from a suprasternal view

A novel method to obtain the aortic pressure waveform using a sequence of B-mode images is developed in this project. An automatic edge detection algorithm is applied to a sequence of longitudinal images of the aortic arch acquired from a suprasternal view. The aortic distension waveform is obtained by measuring the distance between the two edges throughout the cardiac cycle. It is then calibrated using the systolic and diastolic pressures from the brachial artery to obtain an estimated pressure waveform. This method was applied to 5 healthy children, pulse pressure amplification and total arterial compliance were calculated from the estimated waveforms.

Cross-sectional Imaging Identifies Flow-mediated Vasodilatation More Accurately Compared with Longitudinal Imaging

OBJECTIVES

The purpose of this study was to evaluate cross-sectional imaging to longitudinal plane imaging for measurement of flow-mediated dilatation (FMD).

BACKGROUND

Accurate and reproducible assessment of FMD as a measure of endothelial function has important implications. Conventional imaging of the brachial artery is in a longitudinal plane. However, the changes in vasodilatation seen are subtle and minimal (10%-20%) in healthy states with an even smaller change in diseased states, thus, affecting interobserver and intraobserver variability and reproducibility.

METHODS

Nine healthy volunteers (5 men, 4 women) between the ages of 25 and 65 years had baseline FMD measurements done using both longitudinal and cross-sectional imaging. Brachial artery was occluded by inflating the sphygmomanometer cuff on the arm at a pressure of 150 mm Hg for 5 minutes. The artery was imaged continuously for 5 minutes postdeflation. The images were recorded digitally on a computer and analyzed for area and diameter changes by user-guided semiautomated boundary detection method described by our group earlier.

RESULTS

The baseline measurements were normalized to 1.00 for both longitudinal and cross-sectional images. After cuff deflation, the mean longitudinal diameter increased to 1.10 +/- 0.04 versus 1.30 +/- 0.17 (P = .007) for the cross-sectional method. The mean longitudinal measurements were 85.7 +/- 13.9 pixels at baseline that increased to 94.3 +/- 13.1 pixels for a mean change of 8.6 +/- 3.1 pixels after cuff deflation, compared with a mean of 8577.4 +/- 2950.8 pixels that increased to 11120.5 +/- 3989.4 pixels for a mean change of 2543 +/- 1552 pixels by the cross-sectional method (P < .001).

CONCLUSIONS

Cross-sectional imaging produced a much larger change in area and pixels compared with longitudinal imaging. This translates into greater sensitivity in detecting small changes produced by FMD.

Verbal working memory and atherosclerosis in patients with cardiovascular disease: an fMRI study

BACKGROUND AND PURPOSE

Intimal-medial thickening (IMT) of the carotid wall is an accepted peripheral marker of atherosclerosis. It is associated with increased risk for myocardial infarction and stroke, and lower attention-executive-psychomotor functioning. The purpose of this study was to examine the relationship between IMT and brain activity during a verbal working memory (VWM) task in patients with cardiovascular disease (CVD).

METHODS

Thirteen CVD patients underwent functional magnetic resonance imaging (fMRI) during a 2-Back VWM task, and B-mode ultrasound of the carotid arteries. IMT was calculated using an automated algorithm based on a validated edge-detection technique. The relationship between IMT and 2-Back-related brain activity was modeled using partial correlations controlling for age and small vessel disease as measured by white matter signal hyperintensities on MRI (WMH).

RESULTS

Higher IMT was associated with lower 2-Back-related signal intensity and in the right middle frontal gyrus, independent of age and WMH.

CONCLUSIONS

IMT may be one mechanism contributing to brain dysfunction in CVD. The blood oxygenation level-dependent (BOLD) contrast appears to be highly sensitive to peripheral vascular health as measured by IMT. Future studies should examine the sensitivity and specificity of the BOLD response for predicting cognitive decline in CVD.

Carotid artery intima-media thickness and cognition in cardiovascular disease

BACKGROUND

Increased carotid artery intima-media thickness (IMT) is a non-invasive marker of systemic arterial disease. Increased IMT has been associated with atherosclerosis, abnormal arterial mechanics, myocardial infarction, and stroke. Given evidence of a relationship between cardiovascular health and attention-executive-psychomotor functioning, the purpose of this study was to examine IMT in relation to neuropsychological test performance in patients with a variety of cardiovascular diagnoses.

METHODS

One hundred and nine participants, ages 55 to 85, underwent neuropsychological assessment and B-mode ultrasound of the left common carotid artery. IMT was calculated using an automated algorithm based on a validated edge-detection technique. The relationship between IMT and measures of language, memory, visual-spatial abilities and attention-executive-psychomotor functioning was modeled using hierarchical linear regression analyses adjusted for age, education, sex, cardiovascular risk, current systolic blood pressure, and history of coronary artery disease (CAD).

RESULTS

Increased IMT was associated with significantly lower performance in the attention-executive-psychomotor domain (IMT beta=-0.26, p<.01), independent of age, education, sex, cardiovascular risk, current systolic blood pressure, and CAD (F(10,100)=3.61, p<.001). IMT was not significantly related to language, memory, or visual-spatial abilities.

CONCLUSIONS

Our findings suggest that, in patients with cardiovascular disease, IMT may be associated with the integrity of frontal subcortical networks responsible for attention-executive-psychomotor performance. Future studies are needed to clarify the mechanisms by which IMT affects cognition and examine potential interactions between increased IMT and other measures of cardiovascular health such as blood pressure variability, cardiac systolic performance, and systemic perfusion.

Rho kinase inhibition improves endothelial function in human subjects with coronary artery disease

Investigations from basic biology suggest that activation of the Rho/Rho kinase pathway reduces the bioavailability of nitric oxide (NO) and thereby promotes atherosclerosis and its clinical complications. Yet, little information is available about the relationship of the Rho/Rho kinase pathway to NO bioavailability in humans with atherosclerosis. Accordingly, we determined whether inhibition of Rho kinase augments NO bioavailability and improves endothelial function in human subjects with coronary artery disease (CAD). Thirteen CAD subjects and 16 age- and sex-matched healthy controls were randomly assigned to receive the Rho kinase inhibitor, fasudil, or placebo for 1 month each in a double-blind crossover trial. Flow-mediated, endothelium-dependent and nitroglycerin-induced, endothelium-independent vasodilation were assessed by brachial artery ultrasonography. Rho kinase activity was measured in peripheral leukocytes. Fasudil increased endothelium-dependent vasodilation in CAD subjects from 9.4+/-1.9% to 13.4+/-1.9% (P=0.001) but not in healthy controls (from 11.3+/-1.4% to 7.7+/-1.1%; P=0.07). Endothelium-independent vasodilation was not affected by fasudil in either CAD or healthy subjects. Fasudil reduced Rho kinase activity by 59+/-18% in CAD subjects (P=0.001) but not in healthy subjects (by 3+/-6%; P=0.60). The change in endothelium-dependent vasodilation achieved with fasudil relative to placebo was inversely proportional to Rho kinase inhibition (ie, greater Rho kinase inhibition was associated with larger improvement in endothelium-dependent vasodilation) (r=-0.48; P=0.01). These findings suggest that Rho/Rho kinase activation promotes endothelial dysfunction in humans with atherosclerosis. Inhibition of the Rho/Rho kinase pathway should provide a useful strategy to restore NO bioavailability in humans with atherosclerosis.

Flow-mediated vasodilation: a diagnostic instrument, or an experimental tool?

Brachial arterial flow-mediated dilation (FMD), assessed by high-resolution ultrasonography, reflects endothelium-dependent vasodilator function. FMD is diminished in patients with atherosclerosis and with coronary risk factors, and improves with risk-reduction therapy. Therefore, the measurement of FMD can be a good prognostic instrument in preventive cardiology, is useful to predict short-term postoperative cardiovascular events in a high-risk population and to assess long-term cardiovascular risk in a lower risk population, and is an excellent experimental tool to detect changes in endothelial function after new therapeutic interventions. In this review article, the pathophysiology of FMD, based on reactive hyperemia, is extensively discussed. Furthermore, an overview is given of the actual clinical indications of FMD measurement.

Radiofrequency ablation in the liver close to the bile ducts: can intraductal cooling offer protection?

BACKGROUND

One complication of radiofrequency ablation (RFA) of the liver is biliary duct damage. Intraductal cooling (IDC) has been proposed as a means of protection.

METHODS

In the first experiment, designed to evaluate the influence of IDC on the RFA procedure per se and on lesion formation, lesions were created in vivo in pig liver with and without IDC. The RFA needle was placed with a 1.5-cm safety margin from the bile ducts. In the second experiment, designed to evaluate the potential protective effects of IDC, lesions were created close to a bile duct with and without IDC.

RESULTS

With the safety margin, the RFA parameters and lesion size were not negatively affected by IDC. Microscopic examination revealed that IDC had a protective effect in most of the lesions created close to a bile duct.

CONCLUSIONS

The IDC procedure was feasible and had no negative effect on the RFA procedure or the lesions. However, the protective effect of IDC was not statistically significant (p = 0.12).

Detection of lumen-intima interface of posterior wall for measurement of elasticity of the human carotid artery

In our series of studies on noninvasive assessment of the regional elasticity of the arterial wall, the displacement gradient (change in thickness) of the arterial wall caused by the heartbeat was measured by the phased-tracking method. Because the displacement gradient corresponds to the strain due to the change in blood pressure, the elasticity can be evaluated from the displacement gradient of the arterial wall and the blood pressure, which are noninvasively measured at the upper arm. In the measurement of the elasticity of the arterial wall by our method, the region in which the elastic modulus is estimated must be assigned beforehand; currently, the lumen-intima boundary of the arterial wall is manually determined by the operator. For the real-time measurement of the elasticity of the arterial wall, a fast, automated method is necessary for detection of the boundary. In this paper, a cost function is proposed for differentiation of the arterial wall from the lumen. The proposed cost function was applied to ultrasound data, which were noninvasively obtained for five human carotid arteries. In comparison with the case of detection using only the amplitude of the echo, the root mean square error between the automatically detected lumen-intima boundary and the manually assigned boundary was significantly improved by using the proposed cost function. Furthermore, the lumen-intima boundary was automatically detected in a short period. Such a method is required for real-time measurement of the elasticity of the arterial wall, though detection of the outer boundary of the adventitia, which is not described in this paper, is also necessary to realize real-time elasticity measurement by our method.

Brachial artery: measurement of flow-mediated dilatation with cross-sectional US--technical validation

Ultrasonographic examination of flow phantoms and the brachial artery of a healthy volunteer undergoing reactive hyperemia was performed. Images were analyzed with a user-guided automated boundary detection (UGABD) algorithm to extract boundaries and measure cross-sectional area. UGABD correctly detected pulsatile vasomotion and measured area within 5% of the true value. A comparison of UGABD versus manual tracing yielded linear correlation of 0.81-0.91. Peak vasodilatation measured in response to reactive hyperemia was 150 times greater in pixel count than that measured with longitudinal imaging. Cross-sectional imaging is more sensitive than longitudinal imaging for measuring flow-mediated dilatation of the brachial artery.

Size and blood flow of central and peripheral arteries in highly trained able-bodied and disabled athletes

In a cross-sectional study, central and peripheral arteries were investigated noninvasively in high-performance athletes and in untrained subjects. The diastolic inner vessel diameter (D) of the thoracic and abdominal aorta, the subclavian artery (Sub), and common femoral artery (Fem) were determined by duplex sonography in 18 able-bodied professional tennis players, 34 able-bodied elite road cyclist athletes, 26 athletes with paraplegia, 17 below-knee amputated athletes, and 30 able-bodied, untrained subjects. The vessel cross-sectional areas (CSA) were set in relation to body surface area (BSA), and the cross-section index (CS-index = CSA/BSA) was calculated. Volumetric blood flow was determined in Sub and Fem via a pulsed-wave Doppler system and was set in relation to heart rate to calculate the stroke flow. A significantly increased D of Sub was found in the racket arm of able-bodied tennis players compared with the opposite arm (19%). Fem of able-bodied road cyclist athletes and of the intact limb in below-knee amputated athletes showed similar increases. D of Fem was lower in athletes with paraplegia (37%) and in below-knee amputated athletes proximal to the lesion (21%) compared with able-bodied, untrained subjects; CS-indexes were reduced 57 and 31%, respectively. Athletes with paraplegia demonstrated a larger D (19%) and a larger CS-index in Sub (54%) than able-bodied, untrained subjects. No significant differences in D and CS-indexes of the thoracic and abdominal aorta were found between any of the groups. The changes measured in Sub and Fem were associated with corresponding alterations in blood flow and stroke flow in all groups. The study suggests that the size and blood flow volume of the proximal limb arteries are adjusted to the metabolic needs of the corresponding extremity musculature and underscore the impact of exercise training or disuse on the structure and the function of the arterial system.

Effect of systolic blood pressure and carotid stiffness on baroreflex gain in elderly subjects

BACKGROUND

Aging is associated with diminished baroreflex sensitivity (gain), which predisposes elderly people to orthostatic hypotension, syncope, and cardiovascular morbidity. Aging is also associated with systolic blood pressure (SBP) elevation and carotid artery stiffness, which may both affect baroreflex gain.

METHODS

We examined the relation between SBP, carotid artery stiffness, and baroreflex gain in 34 healthy elderly (71 +/- 4 years) and 10 healthy young (31 +/- 3 years) subjects. SBP (Finapres) and carotid artery stiffness (ultrasound measures of relative carotid artery diameter changes during each blood pressure pulse) were measured. The gain of the transfer function relating the R-R interval to SBP fluctuations at a frequency of 0.05-0.15 Hz was used to assess cardiovagal baroreflex gain.

RESULTS

Elderly subjects had higher carotid artery stiffness (14.2 +/- 5.1 vs 6.6 +/- 1.8, p <.05), higher SBP (146 +/- 24 vs 125 +/- 8 mmHg, p =.012), and lower baroreflex gain (8.2 +/- 6.4 vs 16.3 +/- 7.4, p <.05) than young subjects. Among all subjects, SBP and carotid artery stiffness both correlated with baroreflex gain (r = -.39, p =.02 for both). Although SBP was related to stiffness across all subjects, this relation was not present among the elderly subjects. Within the elderly group, only SBP was independently related to baroreflex gain (R(2) =.51, p =.009).

CONCLUSIONS

SBP elevation in elderly people may affect the neural or cardiac response to blood pressure fluctuations, independent of the mechanical properties of barosensory regions in the carotid artery. Future studies should examine the effect of pharmacologic treatment of hypertension on baroreflex gain in elderly people.

Ambulatory blood pressure, left ventricular mass, and conduit artery function late after successful repair of coarctation of the aorta

OBJECTIVES

We sought to evaluate the determinants of hypertension during daily life and left ventricular (LV) hypertrophy in patients with successfully repaired coarctation of the aorta (CoA), as well as their relationship to abnormalities of arterial function.

BACKGROUND

Arterial hypertension may recur late after repair of CoA, which is related to a more adverse outcome. Furthermore, patients with normal resting blood pressure (BP) may have hypertension during daily life and LV hypertrophy. The determinants of these two adverse prognostic factors have not been investigated.

METHODS

We studied 72 patients (9 to 58 years of age) who underwent coarctation repair at age 0.1 to 480 months (42 [60%] at <1 year) and had been followed up for 155 +/- 76 months. They underwent ambulatory BP monitoring, echocardiography for LV mass, studies of brachial artery responses to flow (i.e., flow-mediated dilation [FMD]) and glyceryl trinitrate (GTN), and determination of pulse wave velocity (PWV) and measures of arterial reactivity and stiffness. Findings were compared with those of 53 healthy volunteers.

RESULTS

Patients had higher 24-h systolic BP and LV mass than controls. Both endothelium-dependent FMD and the response to the smooth muscle dilator GTN were reduced, and PWV was increased. There was a negative independent correlation between GTN response and 24-h systolic BP in both patients and control subjects. Systolic BP at 24 h was an independent predictor of LV mass, having an accentuated impact in coarctation subjects as compared with controls.

CONCLUSIONS

In patients with repaired coarctation, reduced vascular reactivity is associated with hypertension during daily life and with increased LV mass, both of which are important predictors for late morbidity and mortality.

Carotid distensibility characterized via the isometric exercise pressor response

Distensibility of the large elastic arteries is a key index for cardiovascular health. Distensibility, usually estimated from resting values in humans, is not a static characteristic but a negative curvilinear function of pressure. We hypothesized that differences in vascular function with gender and age may only be recognized if distensibility is quantified over a range of pressures. We used isometric handgrip exercise to induce progressive increases in pressures and carotid diameters, thereby enhancing the characterization of distensibility. In 30 volunteers, evenly distributed by gender and age across the third to fifth decades of life, we derived pulsatile distensibility slopes as a function of arterial pressure for a dynamic distensibility index and compared it with a traditional static index at a reference pressure of 95 mmHg. We also assessed intima-media thickness (IMT). We found that women had greater distensibility slopes within each decade, despite comparable IMT. Furthermore, declines in distensibility slope with increasing age were correlated to increased IMT. The static distensibility index failed to show gender-related differences in distensibility but did show age-related differences. Our results indicate that gender- and age-related differences can be manifest even in young, healthy adults and may only be identified with techniques that assess carotid distensibility across a range of pressures.

Noninvasive Studies of Coronary and Peripheral Arterial Blood-flow

Noninvasive vascular imaging may identify the high-risk, asymptomatic atherosclerotic patient who will substantially benefit from aggressive preventive therapies. Endothelium is a key player in the early stages of atherogenesis. Positron emission tomography (PET) and ultrasound-measured brachial artery vasoreactivity have emerged as potentially useful tools for the identification of endothelial dysfunction and, as such, early atherosclerosis. Both have been used successfully to demonstrate the association between endothelial dysfunction and established coronary artery disease risk factors, as well as clinically evident coronary artery disease. Abnormal coronary endothelial function recently has been associated with poor clinical outcomes in long-term follow-up studies. Given the close association between endothelial function in the coronary and peripheral circulation, there is particular promise for the validation of brachial artery vasoreactivity as a clinically useful tool. Finally, surveillance of endothelial function with these techniques may prove helpful in guiding aggressiveness of antiatherosclerotic therapy and effectiveness of new regimens.

Mental stress response, arterial stiffness, and baroreflex sensitivity in healthy aging

This study examined the relationship of pressor responses during mental stress to arterial stiffness and baroreflex sensitivity. Hemodynamic responses of 24 healthy individuals (51-86 years old) to two mental stress tasks (math and speech) were compared with common carotid artery mechanical stiffness and autonomic nervous system regulation of blood pressure as measured by using the modified Oxford technique. At the ages studied, no effect of age on stress task responsiveness, carotid stiffness, or baroreflex sensitivity was observed. Carotid stiffness and baroreflex sensitivity demonstrated a strong inverse relation. Change in heart rate during the speech task was correlated with arterial stiffness, and the increase in mean arterial pressure was associated with carotid stiffness and was inversely correlated to baroreflex sensitivity. These associations suggest that acute hemodynamic reactions to mental stress among healthy adults are determined, in part, by structural properties of arterial vessels and sensitivity of arterial baroreflex. These observations may provide a mechanistic link between the physiology of cardiovascular reactivity to stress and risk of cardiovascular events in middle-aged and older individuals.

Guidelines for the ultrasound assessment of endothelial-dependent flow-mediated vasodilation of the brachial artery: a report of the International Brachial Artery Reactivity Task Force

Endothelial function is thought to be an important factor in the pathogenesis of atherosclerosis, hypertension and heart failure. In the 1990s, high-frequency ultrasonographic imaging of the brachial artery to assess endothelium-dependent flow-mediated vasodilation (FMD) was developed. The technique provokes the release of nitric oxide, resulting in vasodilation that can be quantitated as an index of vasomotor function. The noninvasive nature of the technique allows repeated measurements over time to study the effectiveness of various interventions that may affect vascular health. However, despite its widespread use, there are technical and interpretive limitations of this technique. State-of-the-art information is presented and insights are provided into the strengths and limitations of high-resolution ultrasonography of the brachial artery to evaluate vasomotor function, with guidelines for its research application in the study of endothelial physiology.

Impaired vascular reactivity in pregnant women with insulin-dependent diabetes mellitus

OBJECTIVE

The purpose of this study was to investigate the vascular function of pregnant women with insulin-dependent diabetes mellitus, using a noninvasive method.

STUDY DESIGN

This was a cross-sectional study that examined vascular function, which was assessed by flow-mediated dilatation of the brachial artery, in 37 pregnant women with insulin-dependent diabetes mellitus and in 37 healthy pregnant women at 20 weeks of gestation. The control of diabetes was also assessed by the measurement of glycosylated hemoglobin. Data were analyzed by 2-sided unpaired t test and multivariate regression analysis.

RESULTS

In the pregnant women with insulin-dependent diabetes mellitus, flow-mediated dilatation of the brachial artery was significantly lower than in healthy pregnant women (6.43% +/- 3.66% vs 9.43% +/- 3.69%, respectively; P =.0008). This difference was apparent even after an adjustment was made for blood vessel diameter, which was different between the 2 populations (P =.01). Flow-mediated dilatation in diabetic women was significantly correlated with the duration of diabetes (P =.01) but not with the levels of glycosylated hemoglobin.

CONCLUSION

Maternal insulin-dependent diabetes mellitus is associated with an impaired vasodilatory response to a blood flow stimulus. This vascular dysfunction is associated with the duration of the diabetes.

Automatic evaluation of arterial diameter variation from vascular echographic images

An automatic procedure for accurate arterial diameter evaluation from B-mode images obtained by diagnostic ultrasound systems is presented. It is used for measuring brachial artery dilation following reactive hyperemia induced by forearm ischemia, which is an appropriate parameter to study endothelial function in humans. B-mode images obtained from the diagnostic ultrasound system are acquired on a personal computer as grey intensity fields (pixels). A completely automatic algorithm is then applied and the artery walls are identified by two discrete sets of points. Artery diameter is evaluated by parabolic least-square approximation. The accuracy and extensive range of applicability of the diameter evaluation procedure were demonstrated both by preliminary analytic test cases and in vivo analyses. Reproducibility of the diameter estimate was assessed by in vivo measurements. The proposed procedure permits fast and accurate analysis of large amounts of data, because it requires no action by the operator. It thus represents a valuable tool for assessment of endothelium-dependent vasodilation, especially in large, multicentric clinical trials.

Non-invasive assessment of arterial distension waveforms using gradient-based hough transform and power Doppler ultrasound imaging

The peripheral arterial vessel often appears as an elliptic shape under the constraints of the surrounding tissues. In this study, the gradient-based Hough transform was used to detect the central location of the ellipse and the lumen area of the arterial vessel non-invasively using power Doppler imaging. Sequential ultrasound images were used to construct arterial distension waveforms in both the major- and minor-axis directions for a few cardiac cycles. The common carotid arteries (CCAs) for nine healthy male volunteers (mean age 24 years), in the sitting position, were investigated in vivo. The CCAs (n = 9) had a mean diameter of 5.83mm, and the pulsatile diameter distension was 13.7+/-1.9%. The brachial artery and dorsalis pedis artery for five healthy male volunteers (mean age 26 years), in the supine position, had mean diameters of 4.03mm and 2.83mm and distensions of 16.7+/-4.6% and 15.5+/-5.4%, respectively. The movement of the arterial centre location during the cardiac cycle reflected the asymmetry of the reaction forces produced by the surrounding soft tissues. The present method can obtain the response of vessel distension to pulse pressure, as well as the constrained conditions of the arteries.

Improved analysis of brachial artery ultrasound using a novel edge-detection software system

Brachial artery ultrasound is commonly employed for noninvasive assessment of endothelial function. However, analysis is observer dependent and susceptible to errors. We describe studies on a computerized edge-detection and wall-tracking software program to allow more accurate and reproducible measurement. In study 1, three purpose-built Perspex phantom arteries, 3.00, 4.00, and 6.00 mm in diameter, were measured with the software. There was a mean bias of 11 microm (P < 0.001 at each level) between known and measured values; the mean resolving power of the software was estimated as 8.3 microm. In study 2, the mean intraobserver coefficient of variation of repeated measures of flow-mediated dilation (FMD) using the software (6.7%) was significantly lower than that for traditional manual measurements using the intima-lumen interfaces (24.8%, P < 0.05) and intima-media interfaces (32.5%, P < 0.05). In study 3, 24 healthy volunteers underwent repeat testing twice within 1 wk; the coefficients of variation for between-visit reproducibility of FMD and response to glyceryl trinitrate using the software were 14.7 and 17.6%, respectively. Assuming 80% power and an alpha of 0.05, eight subjects with matched controls would be required, in a parallel designed study, to detect an absolute 2.5% change in FMD. In summary, we have developed a semiautomated computerized vascular ultrasound analysis system that will improve the power of clinical intervention studies to detect small changes in arterial diameter.

Quantification of mechanical and neural components of vagal baroreflex in humans

Traditionally, arterial baroreflex control of vagal neural outflow is quantified by heart period responses to falling and/or rising arterial pressures (ms/mm Hg). However, it is arterial pressure-dependent stretch of barosensory vessels that determines afferent baroreceptor responses, which, in turn, generate appropriate efferent cardiac vagal outflow. Thus, mechanical transduction of pressure into barosensory vessel stretch and neural transduction of stretch into vagal outflow are key steps in baroreflex regulation that determine the conventional integrated input-output relation. We developed a novel technique for direct estimation of gain in both mechanical and neural components of integrated cardiac vagal baroreflex control. Concurrent, beat-by-beat measures of arterial pressures (Finapres), carotid diameters (B-mode ultrasonography), and R-R intervals (ECG lead II) were made during bolus vasoactive drug infusions (modified Oxford technique) in 16 healthy humans. The systolic carotid diameter/pressure relationship (r(2)=0.79+/-0.008, mean+/-SEM) provided a gain estimate of dynamic mechanical transduction of pressure into a baroreflex stimulus. The R-R interval/systolic diameter relationship (r(2)=0.77+/-0.009) provided a gain estimate of afferent-efferent neural transduction of baroreflex stimulus into a vagal response. Variance between repeated measures for both estimates was no different than that for standard gain (P>0.40). Moreover, in these subjects, the simple product of the 2 estimates almost equaled standard baroreflex gain (ms/mm Hg=0.98x+2.27; r(2)=0.93, P=0.001). This technique provides reliable information on key baroreflex components not distinguished by standard assessments and gives insight to dynamic mechanical and neural events during acute changes in arterial pressure.

Assessment of endothelial function in normal twin pregnancy

OBJECTIVE

To assess the maternal endothelial function in normal twin pregnancy.

DESIGN

Cross-sectional study.

SUBJECTS

Endothelial function was investigated in 74 women with normal twin pregnancy at 11-30 weeks of gestation and the results were compared to previous reported findings in 98 women with normal singleton pregnancy and 19 non-pregnant controls.

METHODS

Endothelial function was assessed by measuring the changes of the brachial artery diameter in response to reactive hyperemia (flow-mediated dilatation) using external high resolution ultrasound.

RESULTS

Flow-mediated dilatation of the brachial artery in both twin and singleton pregnancies was significantly higher than in non-pregnant women (P = 0.002 and P = 0.02, respectively). However, there was no significant difference in flow-mediated dilatation between women with twin and singleton pregnancy (9.61 +/- 4.36 vs. 8.84 +/- 3.18, P = 0.38). Resting vessel size, baseline flow and reactive hyperemia did not change significantly with gestation in twin pregnancy and were similar to values in singleton pregnancies and controls.

CONCLUSION

Our findings indicate that although in pregnancy endothelial function is enhanced, this change may not be affected by the number of fetoplacental units present.

Effect of acute blood pressure reduction on endothelial function in the brachial artery of patients with essential hypertension

OBJECTIVES

To evaluate the effect of acute blood pressure reduction on endothelium-dependent vasodilation in the peripheral circulation of essential hypertensive patients.

DESIGN

A parallel group study; endothelial function measured in 64 essential hypertensive patients before and after (2 h) treatment with nifedipine (20 mg, n = 32) or captopril (50 mg, n = 32), p.o., randomly assigned.

METHODS

In hypertensive patients, we evaluated flow-mediated, endothelium-dependent dilation (FMD, high resolution ultrasound) of the brachial artery compared with endothelium-independent response to glyceryl trinitrate (GTN, 25 microg s.l.). Automatic computerized analysis was used to measure brachial artery diameter on end-diastolic frames acquired every second during the study. Sixty-six healthy normotensive subjects were also evaluated to assess the presence of endothelial dysfunction in hypertensive patients.

RESULTS

Hypertensive patients showed a significantly (P< 0.01) lower FMD (5.9 +/- 2.5%) as compared to healthy controls (7.7 +/- 3.8%). The response to GTN was similar in normotensive subjects (7.5 +/- 3.1%) and hypertensive patients (7.2 +/- 6.5%). At baseline brachial artery diameter, FMD and response to GTN were similar in the nifedipine- and captopril-treated groups. Nifedipine and captopril similarly reduced blood pressure, but only nifedipine increased heart rate. Acute nifedipine, but not captopril, significantly (P< 0.01) increased brachial artery diameter, while FMD and response to GTN were not modified after nifedipine or captopril.

CONCLUSIONS

Endothelial dysfunction in the brachial artery of essential hypertensive patients is not improved by acute blood pressure reduction.

An adaptive template-matching method and its application to the boundary detection of brachial artery ultrasound scans

We developed an adaptive template-matching method for vessel wall boundary detection in brachial artery ultrasound (US) scans. The computer-aided identification of lumen-intima and media-adventitia boundaries of the brachial artery US scan is a critical step for flow-mediated vasodilator response measurement, which has become an increasingly important tool in both clinical and research applications. The adaptive template we propose in this paper is a combination of two parameterized Gaussian envelopes that approximates the US pulse envelope. The algorithm for template matching is cast as a constrained nonlinear least squares problem. A best match between the template and the observed US scan line signal results in a set of optimum parameters of the adaptive template, and the location of the boundaries is directly computed from these parameters. We present the results of applying our method to synthetic and clinical data, showing that the adaptive template-matching method provides superior accuracy in detecting the media-adventitia boundaries of both the near wall and the far wall of the vessel to that of conventional edge-detection methods.

Heterogenous nature of flow-mediated dilatation in human conduit arteries in vivo: relevance to endothelial dysfunction in hypercholesterolemia

Flow-mediated dilatation (FMD) of conduit arteries is dependent on an intact endothelium, although the mechanisms are not fully understood. Using high-resolution ultrasound, we examined the role of endothelial mediators in radial artery dilatation in response to transient (short period of reactive hyperemia) and sustained (prolonged period of reactive hyperemia, hand warming, or an incremental infusion of acetylcholine into the distal radial artery) hyperemia. After short episodes of reactive hyperemia, FMD was abolished by local infusion of the nitric oxide synthesis inhibitor N:(G)monomethyl-L-arginine (5.3+/-1.2% versus 0.7+/-0.7%, P:<0.001). In contrast, basal vessel diameter and dilatation after prolonged episodes of reactive hyperemia, hand warming, and distal infusion of acetylcholine were not attenuated by nitric oxide synthesis inhibition. Inhibition of cyclooxygenase or local autonomic nervous system blockade also had no effect on FMD. Patients with hypercholesterolemia exhibited reduced FMD in response to transient hyperemia, but the response to sustained hyperemia was normal. These data suggest heterogeneity of endothelial responses to blood flow that are dependent on the characteristics of the flow stimulus. Dilatation after brief episodes of hyperemia is mediated by release of nitric oxide, whereas dilatation during sustained hyperemia is unaffected by NO synthesis inhibition. Hypercholesterolemia seems to differentially affect these pathways with impairment of the nitric oxide-dependent pathway and preservation of non nitric oxide-mediated dilatation to sustained flow stimuli.

Mental stress induces transient endothelial dysfunction in humans

BACKGROUND

Mental stress has been linked to increased morbidity and mortality in coronary artery disease and to atherosclerosis progression. Experimental studies have suggested that damage to the endothelium may be an important mechanism.

METHODS AND RESULTS

Endothelial function was studied in 10 healthy men (aged 50. 4+/-9.6 years) and in 8 non-insulin-dependent diabetic men (aged 52. 0+/-7.2 years). Brachial artery flow-mediated dilation (FMD, endothelium dependent) and response to 50 microg of sublingual glyceryl trinitrate (GTN, endothelium independent) were measured noninvasively by use of high-resolution ultrasound before and after (30, 90, and 240 minutes) a standardized mental stress test. The same protocol without mental stress was repeated on a separate occasion in the healthy men. In healthy subjects, FMD (5.0+/-2.1%) was significantly (P:<0.01) reduced at 30 and 90 minutes after mental stress (2.8+/-2.3% and 2.3+/-2.4%, respectively) and returned toward normal after 4 hours (4.1+/-2.0%). Mental stress had no effect on the response to GTN. In the repeated studies without mental stress, FMD did not change. The diabetic subjects had lower FMD than did the control subjects (3.0+/-1.5% versus 5.0+/-2.1%, respectively; P:=0.02) but showed no changes in FMD (2.7+/-1.1% after 30 minutes, 2.8+/-1.9% after 90 minutes, and 3.1+/-2.3% after 240 minutes) or GTN responses after mental stress.

CONCLUSIONS

These findings suggest that brief episodes of mental stress, similar to those encountered in everyday life, may cause transient (up to 4 hours) endothelial dysfunction in healthy young individuals. This might represent a mechanistic link between mental stress and atherogenesis.

Ultrasound measurement of brachial flow-mediated vasodilator response

Brachial artery flow-mediated vasodilation is increasingly used as a measure of endothelial function. High resolution ultrasound provides a noninvasive method to observe this flow-mediated vasodilation by monitoring the diameter of the artery over time following a transient flow stimulus. Since hundreds of ultrasound images are required to continuously monitor brachial diameter for the 2-3 min during which the vasodilator response occurs, an automated diameter estimation is desirable. However, vascular ultrasound images suffer from structural noise caused by the constructive and destructive interference of the backscattered signals, and the true boundaries of interest that define the diameter are frequently obscured by the multiple-layer structure of the vessel wall. These problems make automated diameter estimation strategies based on the detection of the vessel wall boundary difficult. We obtain a robust automated measurement of the vasodilator response by automatically locating the artery using a variable window method, which gives both the lumen center and width. The vessel wall boundary is detected by a global constraint deformable model, which is insensitive to the structural noise in the boundary area. The ambiguity between the desired boundary and other undesired boundaries is resolved by a spatiotemporal strategy. Our method provides excellent reproducibility both for interreader and intrareader analyzes of percent change in diameter, and has been successfully used in analyzing over 4000 brachial flow-mediated vasodilation scans from several medical centers in the United States.