Koen D. Reesink

The dicrotic notch as alternative time-reference point to measure local pulse wave velocity in the carotid artery by means of ultrasonography.

Objectives Increased arterial stiffness is associated with cardiovascular disease. Its applicability in individual patient management, however, is limited due to lack of reliable methods. We developed a method to measure arterial stiffness by means of local pulse wave velocity (PWV), using multiple M-mode ultrasound and the dicrotic notch (PWVdn) rather than the systolic foot (PWVsf) as time-reference point. Methods Systolic foot and dicrotic notch were determined in 14 simultaneously recorded distension waveforms obtained in young and older participants (mean age 26 and 59 years). Linear regression was performed on echo-line position and time-reference point, resulting in a local PWV estimate, either PWVsf or PWVdn. Results PWVdn, at about mean arterial pressure, had a better intra-individual variability (0.6 m/s) than PWVsf (1.1 m/s). The expected difference in stiffness between the two age categories was identified by PWVdn (P < 0.0001), but not by PWVsf. Moreover, in contrast to PWVsf, PWVdn showed a significant correlation with relative distension (r2 = 0.56) and the local distensibility coefficient (r2 = 0.52). Conclusion PWVdn is a noninvasive and suitable measure of arterial stiffness: it has a good reproducibility, discriminates well between age groups, and correlates with local distensibility. PWVdn does not require additional assessment of distance or local pulse pressure. Furthermore, PWVdn is measured locally, at near-mean arterial pressure, thereby better reflecting the effective arterial stiffness, which determines the load the left ventricle is subjected to as it ejects blood.

Pleiotropic Benefit of Monomeric and Oligomeric Flavanols on Vascular Health - A Randomized Controlled Clinical Pilot Study

Background Cardiovascular diseases are expanding to a major social-economic burden in the Western World and undermine mans deep desire for healthy ageing. Epidemiological studies suggest that flavanol-rich foods (e.g. grapes, wine, chocolate) sustain cardiovascular health. For an evidenced-based application, however, sound clinical data on their efficacy are strongly demanded. Methods In a double-blind, randomized, placebo-controlled intervention study we supplemented 28 male smokers with 200 mg per day of monomeric and oligomeric flavanols (MOF) from grape seeds. At baseline, after 4 and 8 weeks we measured macro- and microvascular function and a cluster of systemic biomarkers for major pathological processes occurring in the vasculature: disturbances in lipid metabolism and cellular redox balance, and activation of inflammatory cells and platelets. Results In the MOF group serum total cholesterol and LDL decreased significantly (P≤0.05) by 5% (n = 11) and 7% (n = 9), respectively in volunteers with elevated baseline levels. Additionally, after 8 weeks the ratio of glutathione to glutathione disulphide in erythrocytes rose from baseline by 22% (n = 15, P<0.05) in MOF supplemented subjects. We also observed that MOF supplementation exerts anti-inflammatory effects in blood towards ex vivo added bacterial endotoxin and significantly reduces expression of inflammatory genes in leukocytes. Conversely, alterations in macro- and microvascular function, platelet aggregation, plasma levels of nitric oxide surrogates, endothelin-1, C-reactive protein, fibrinogen, prostaglandin F2alpha, plasma antioxidant capacity and gene expression levels of antioxidant defense enzymes did not reach statistical significance after 8 weeks MOF supplementation. However, integrating all measured effects into a global, so-called vascular health index revealed a significant improvement of overall vascular health by MOF compared to placebo (P≤0.05). Conclusion Our integrative multi-biomarker approach unveiled the pleiotropic vascular health benefit of an 8 weeks supplementation with 200 mg/d MOF in humans. Trial Registration ClinicalTrials.gov NCT00742287

Noninvasive Assessment of Arterial Stiffness Should Discriminate Between Systolic and Diastolic Pressure Ranges

Arterial stiffening plays an important role in the development of hypertension and cardiovascular diseases. The intrinsically nonlinear (ie, pressure-dependent) elastic behavior of arteries may have serious consequences for the accuracy and interpretation of arterial stiffness measurements and, ultimately, for individual patient management. We determined aortic pressure and common carotid artery diameter waveforms in 21 patients undergoing cardiac catheterization. The individual pressure-area curves were described using a dual exponential analytic model facilitating noise-free calculation of incremental pulse wave velocity. In addition, compliance coefficients were calculated separately in the diastolic and systolic pressure ranges, only using diastolic, dicrotic notch, and systolic data points, which can be determined noninvasively. Pulse wave velocity at systolic pressure exhibited a much stronger positive correlation with pulse pressure (P<0.001) and age (P=0.012) than pulse wave velocity at diastolic pressure. Patients with an elevated systolic blood pressure (>140 mm Hg) had a 2.5-times lower compliance coefficient in the systolic pressure range than patients with systolic blood pressures <140 mm Hg (P=0.002). Most importantly, some individuals, with comparable age or pulse pressure, had similar diastolic but discriminately different systolic pulse wave velocities and compliance coefficients. We conclude that noninvasive assessment of arterial stiffness could and should discriminate between systolic and diastolic pressure ranges to more precisely characterize arterial function in individual patients.

In vivo high-resolution structural imaging of large arteries in small rodents using two-photon laser scanning microscopy

In vivo (molecular) imaging of the vessel wall of large arteries at subcellular resolution is crucial for unraveling vascular pathophysiology. We previously showed the applicability of two-photon laser scanning microscopy (TPLSM) in mounted arteries ex vivo. However, in vivo TPLSM has thus far suffered from in-frame and between-frame motion artifacts due to arterial movement with cardiac and respiratory activity. Now, motion artifacts are suppressed by accelerated image acquisition triggered on cardiac and respiratory activity. In vivo TPLSM is performed on rat renal and mouse carotid arteries, both surgically exposed and labeled fluorescently (cell nuclei, elastin, and collagen). The use of short acquisition times consistently limit in-frame motion artifacts. Additionally, triggered imaging reduces between-frame artifacts. Indeed, structures in the vessel wall (cell nuclei, elastic laminae) can be imaged at subcellular resolution. In mechanically damaged carotid arteries, even the subendothelial collagen sheet (approximately 1 microm) is visualized using collagen-targeted quantum dots. We demonstrate stable in vivo imaging of large arteries at subcellular resolution using TPLSM triggered on cardiac and respiratory cycles. This creates great opportunities for studying (diseased) arteries in vivo or immediate validation of in vivo molecular imaging techniques such as magnetic resonance imaging (MRI), ultrasound, and positron emission tomography (PET).

Reference values for local arterial stiffness. Part A: carotid artery.

Objective: Non-invasive measures of common carotid artery properties, such as diameter and distension, and pulse pressure, have been widely used to determine carotid artery distensibility coefficient – a measure of carotid stiffness (stiffness ∼1/distensibility coefficient). Carotid stiffness has been associated with incident cardiovascular disease (CVD) and may therefore be a useful intermediate marker for CVD. We aimed to establish age and sex-specific reference intervals of carotid stiffness. Methods: We combined data on 22 708 individuals (age range 15–99 years, 54% men) from 24 research centres worldwide. Individuals without CVD and established cardiovascular risk factors constituted a healthy sub-population (n = 3601, 48% men) and were used to establish sex-specific equations for percentiles of carotid distensibility coefficient across age. Results: In the sub-population without CVD and treatment (n = 12 906, 52% men), carotid distensibility coefficient Z-scores based on these percentile equations were independently and negatively associated, in men and women, respectively, with diabetes {−0.28 [95% confidence interval (CI) −0.41; −0.15] and −0.27 (−0.43; −0.12)}, mean arterial pressure [−0.26 (−0.29; −0.24) and −0.32 (−0.35; −0.29)], total-to-high-density lipoprotein cholesterol ratio [−0.05 (−0.09; −0.02) and −0.05 (−0.11; 0.01)] and BMI [−0.06 (−0.09; −0.04) and −0.05 (−0.08; −0.02)], whereas these were positively associated with smoking [0.30 (0.24; 0.36) and 0.24 (0.18; 0.31)]. Conclusions: We estimated age and sex-specific percentiles of carotid stiffness in a healthy population and assessed the association between cardiovascular risk factors and carotid distensibility coefficient Z-scores, which enables comparison of carotid stiffness values between (patient) groups with different cardiovascular risk profiles, helping interpretation of such measures.

Critical Appraisal of Targeted Ultrasound Contrast Agents for Molecular Imaging in Large Arteries

Molecular imaging may provide new insights into the early detection and development of atherosclerosis before first symptoms occur. One of the techniques in use employs noninvasive ultrasound. In the past decade, experimental and clinical validation studies showed that for the microcirculation targeted ultrasound contrast agents, such as echogenic liposomes, microbubbles and perfluorocarbon emulsions, do improve visualization of specific structures. For large arteries, however, successful application is less obvious. In this review, we will address the challenges for molecular imaging of large arteries. We will discuss the problems encountered in the use of targeted ultrasound contrast agents presently available, mainly based on data obtained in flow chambers and animal studies because clinical studies are lacking. We conclude that molecular imaging of activated endothelium in large- and middle-sized arteries by site-specific accumulation of contrast material is still difficult to achieve due to wall shear stress conditions in these vessels.

The change in arterial stiffness over the cardiac cycle rather than diastolic stiffness is independently associated with left ventricular mass index in healthy middle-aged individuals

Background: The current standard for arterial stiffness assessment, aortic pulse wave velocity (aPWV), is measured at diastolic pressure. Arterial stiffness, however, is pressure dependent. At the carotid artery level, the degree of this dependency can be quantified as the difference (&Dgr;PWV) between systolic and diastolic (cPWVd) carotid pulse wave velocity. Biomechanically, a greater &Dgr;PWV implies greater increases in left ventricular afterload with physical activity. Therefore, we hypothesized, that &Dgr;PWV is more strongly associated with left ventricular mass index (LVMI) than aPWV and cPWVd. Methods: In 1776 healthy individuals from the Asklepios cohort (age 35–55 years), &Dgr;PWV was obtained from combined carotid artery ultrasound and tonometry recordings. Multiple linear regression analysis was performed to investigate the associations of &Dgr;PWV, cPWVd and aPWV with LVMI, adjusting for age, sex, mean blood pressure (MBP), central pulse pressure, and other possible confounders. Results: &Dgr;PWV was 2.4 ± 1.2 m/s (mean ± SD), ranging from 0.8 m/s, indicating almost constant arterial stiffness over the cardiac cycle, to 4.4 m/s, reflecting substantial pressure dependency. &Dgr;PWV was significantly associated with LVMI (&bgr; of 2.46 g/m1.7 per m/s, P < 0.001), even after full adjustment (&bgr; of 0.56 g/m1.7 per m/s, P = 0.03). cPWVd and aPWV had clear crude associations with LVMI (P < 0.001), but lost significance after adjustment (&bgr; of −0.48 and −0.33 g/m1.7 per m/s, with P = 0.11 and 0.2, respectively). Conclusion: The change in arterial stiffness over the cardiac cycle, rather than diastolic stiffness, is independently associated with LVMI in healthy middle-aged individuals. Therefore, the pressure dependency of arterial stiffness should be considered in cardiovascular risk assessment.

Pressure-dependence of arterial stiffness: potential clinical implications.

Background: Arterial stiffness measures such as pulse wave velocity (PWV) have a known dependence on actual blood pressure, requiring consideration in cardiovascular risk assessment and management. Given the impact of ageing on arterial wall structure, the pressure-dependence of PWV may vary with age. Methods: Using a noninvasive model-based approach, combining carotid artery echo-tracking and tonometry waveforms, we obtained pressure-area curves in 23 hypertensive patients at baseline and after 3 months of antihypertensive treatment. We predicted the follow-up PWV decrease using modelled baseline curves and follow-up pressures. In addition, on the basis of these curves, we estimated PWV values for two age groups (mean ages 41 and 64 years) at predefined hypertensive (160/90 mmHg) and normotensive (120/80 mmHg) pressure ranges. Results: Follow-up measurements showed a near 1 m/s decrease in carotid PWV when compared with baseline, which fully agreed with our model-prediction given the roughly 10 mmHg decrease in diastolic pressure. The stiffness-blood pressure-age pattern was in close agreement with corresponding data from the ‘Reference Values for Arterial Stiffness’ study, linking the physical and empirical bases of our findings. Conclusion: Our study demonstrates that the innate pressure-dependence of arterial stiffness may have implications for the clinical use of arterial stiffness measurements, both in risk assessment and in treatment monitoring of individual patients. We propose a number of clinically feasible approaches to account for the blood pressure effect on PWV measurements.

Confluence of incident and reflected waves interferes with systolic foot detection of the carotid artery distension waveform

Objectives Local pulse wave velocity, a direct measure of arterial stiffness, can be measured using the systolic foot of the pressure waveform as the time reference point. The accuracy and precision of systolic foot identification, which may be disturbed by early wave reflections, heavily affects pulse wave transit time measurements. We investigated within subjects the existence of early wave reflections and their interference with systolic foot identification. Methods Fourteen ultrasound-derived distension waveforms, spaced over 16.4 mm, were simultaneously recorded in the CCA 3 cm proximal of the bifurcation of 12 young subjects. The second derivatives of the distension waveforms were calculated to identify the systolic foot and an inflection point preceding systolic peak distension. Pulse wave transit time was calculated as the time difference between the most proximal and most distal time-point, using either the systolic foot or the inflection point. The time to reflection (ΔTSF_IP) was defined as the time difference between the systolic foot and the inflection point. Results Both transit times (TTSF and TTIP) could be determined with good intrasubject precision: 0.7 and 1.4 ms, respectively. The systolic foot is running forward, TTSF = 3.1 ± 0.9 ms, whereas the inflection point appears to run backward, TTIP = −3.9 ± 1.4 ms. ΔTSF_IP was 44.3 ± 8.8 ms. Conclusion Despite the good intrasubject reproducibility, confluence of incident and reflected waves disturbs identification and discrimination of the systolic foot and the inflection point, resulting in biased estimates. Therefore both points are unsuitable for local pulse transit time measurements in the common carotid artery.

Reference values for local arterial stiffness. Part B : femoral artery

Objective: Carotid-femoral pulse wave velocity (PWV) is considered the gold standard measure of arterial stiffness, representing mainly aortic stiffness. As compared with the elastic carotid and aorta, the more muscular femoral artery may be differently associated with cardiovascular risk factors (CV-RFs), or, as shown in a recent study, provide additional predictive information beyond carotid-femoral PWV. Still, clinical application is hampered by the absence of reference values. Therefore, our aim was to establish age and sex-specific reference values for femoral stiffness in healthy individuals and to investigate the associations with CV-RFs. Methods: Femoral artery distensibility coefficient, the inverse of stiffness, was calculated as the ratio of relative diastolic-systolic distension (obtained from ultrasound echo-tracking) and pulse pressure among 5069 individuals (49.5% men, age range: 15–87 years). Individuals without cardiovascular disease (CVD), CV-RFs and medication use (n = 1489; 43% men) constituted a healthy subpopulation used to establish sex-specific equations for percentiles of femoral artery distensibility coefficient across age. Results: In the total population, femoral artery distensibility coefficient Z-scores were independently associated with BMI, mean arterial pressure (MAP) and total to high-density lipoprotein (HDL) cholesterol ratio. Standardized &bgr;s, in men and women, respectively, were −0.18 [95% confidence interval (95% CI) −0.23 to −0.13] and −0.19 (−0.23 to −0.14) for BMI; −0.13 (−0.18 to −0.08) and −0.05 (−0.10 to −0.01) for MAP; and −0.07 (−0.11 to −0.02) and −0.16 (−0.20 to −0.11) for total-to-HDL cholesterol ratio. Conclusion: In young and middle-aged men and women, normal femoral artery stiffness does not change substantially with age up to the sixth decade. CV-RFs related to metabolic disease are associated with femoral artery stiffness.