Pulse wave analysis of the aortic pressure waveform in severe left ventricular systolic dysfunction

In vitro cardiovascular system emulator (bioreactor) for the simulation of normal and diseased conditions with and without mechanical circulatory support

This article presents a new device designed to simulate in vitro flow rates, pressures, and other parameters representing normal and diseased conditions of the human cardiovascular system. Such devices are sometimes called bioreactors or "mock" simulator of cardiovascular loops (SCVLs) in literature. Most SCVLs simulate the systemic circulation only and have inherent limitations in studying the interaction of left and right sides of circulation. Those SCVLs that include both left and right sides of the circulation utilize header reservoirs simulating cycles with constant atrial pressures. The SCVL described in this article includes models for all four chambers of the heart, and the systemic and pulmonary circulation loops. Each heart chamber is accurately activated by a separate linear motor to simulate the suction and ejection stages, thus capturing important features in the perfusion waveforms. Four mechanical heart valves corresponding to mitral, pulmonary, tricuspid, and aortic are used to control the desired unidirectional flow. This SCVL can emulate different physiological and pathological conditions of the human cardiovascular system by controlling the different parameters of blood circulation through the vascular tree (mainly the resistance, compliance, and elastance of the heart chambers). In this study, four cases were simulated: healthy, congestive heart failure, left ventricular diastolic dysfunction conditions, and left ventricular dysfunction with the addition of a mechanical circulatory support (MCS) device. Hemodynamic parameters including resistance, pressure, and flow have been investigated at aortic sinus, carotid artery, and pulmonary artery, respectively. The addition of an MCS device resulted in a significant reduction in mean blood pressure and re-establishment of cardiac output. In all cases, the experimental results are compared with human physiology and numerical simulations. The results show the capability of the SCVL to replicate various physiological and pathological conditions with and without MCS.

Tenascin-X, collagen, and Ehlers-Danlos syndrome: tenascin-X gene defects can protect against adverse cardiovascular events

Long thought to be two separate syndromes, Ehlers-Danlos syndrome hypermobility type (EDS-HT) and benign joint hypermobility syndrome (BJHS) appear on close examination to represent the same syndrome, with virtually identical clinical manifestations. While both EDS-HT and BJHS were long thought to lack the genetic loci of other connective tissue disorders, including all other types of EDS, researchers have discovered a genetic locus that accounts for manifestations of both EDS-HT and BJHS in a small population of patients. However, given the modest sample size of these studies and the strong correlation between serum levels of tenascin-X with clinical symptoms of both EDS-HT and BJHS, strong evidence exists for the origins of both types of hypermobility originating in haploinsufficiency or deficiency of the gene TNXB, responsible for tenascin-X. Tenascin-X regulates both the structure and stability of elastic fibers and organizes collagen fibrils in the extra-cellular matrix (ECM), impacting the rigidity or elasticity of virtually every cell in the body. While the impacts of tenascin-X insufficiency or deficiency on the skin and joints have received some attention, its potential cardiovascular impacts remain relatively unexplored. Here we set forth two novel hypotheses. First, TNXB haploinsufficiency or deficiency causes the range of clinical manifestations long identified with both EDS-HT and BJHS. And, second, that haploinsufficiency or deficiency of TNXB may provide some benefits against adverse cardiovascular events, including heart attack and stroke, by lowering levels of arterial stiffness associated with aging, as well as by enhancing accommodation of accrued atherosclerotic plaques. This two-fold hypothesis provides insights into the mechanisms underlying the syndromes previous identified with joint hypermobility, at the same time the hypothesis also sheds light on the role of the composition of the extracellular matrix and its impacts on endothelial sheer stress in adverse cardiovascular events.

Increased wave reflection and ejection duration in women with chest pain and nonobstructive coronary artery disease: ancillary study from the Women's Ischemia Syndrome Evaluation

OBJECTIVE

Wave reflections augment central aortic SBP and increase systolic pressure time integral (SPTI) thereby increasing left ventricular (LV) afterload and myocardial oxygen (MVO2) demand. When increased, such changes may contribute to myocardial ischemia and angina pectoris, especially when aortic diastolic time is decreased and myocardial perfusion pressure jeopardized. Accordingly, we examined pulse wave reflection characteristics and diastolic timing in a subgroup of women with chest pain (Women's Ischemia Syndrome Evaluation, WISE) and no obstructive coronary artery disease (CAD).

METHODS

Radial artery BP waveforms were recorded by applanation tonometry, and aortic BP waveforms derived. Data from WISE participants were compared with data from asymptomatic women (reference group) without chest pain matched for age, height, BMI, mean arterial BP, and heart rate.

RESULTS

Compared with the reference group, WISE participants had higher aortic SBP and pulse BP and ejection duration. These differences were associated with increased augmentation index and reflected pressure wave systolic duration. These modifications in wave reflection characteristics were associated with increased SPTI and wasted LV energy (Ew) and a decrease in pulse pressure amplification, myocardial viability ratio, and diastolic pressure time fraction.

CONCLUSION

WISE participants with no obstructive CAD have changes in systolic wave reflections and diastolic timing that increase LV afterload, MVO2 demand, and Ew with the potential to reduce coronary artery perfusion. These alterations in cardiovascular function contribute to an undesirable mismatch in the MVO2 supply/demand that promotes ischemia and chest pain and may contribute to, or increase the severity of, future adverse cardiovascular events.

Plasma concentrations of extracellular matrix protein fibulin-1 are related to cardiovascular risk markers in chronic kidney disease and diabetes

BACKGROUND

Fibulin-1 is one of a few extracellular matrix proteins present in blood in high concentrations. We aimed to define the relationship between plasma fibulin-1 levels and risk markers of cardiovascular disease.

METHODS

Plasma fibulin-1 was determined in subjects with chronic kidney disease (n = 32; median age 62.5, inter-quartile range 51 - 73 years) and 60 age-matched control subjects. Among kidney disease patients serological biomarkers related to cardiovascular disease (fibrinogen, interleukin 6, C-reactive protein) were measured. Arterial applanation tonometry was used to determine central hemodynamic and arterial stiffness indices.

RESULTS

We observed a positive correlation of fibulin-1 levels with age (r = 0.38; p = 0.033), glycated hemoglobin (r = 0.80; p = 0.003), creatinine (r = 0.35; p = 0.045), and fibrinogen (r = 0.39; p = 0.027). Glomerular filtration rate and fibulin-1 were inversely correlated (r = -0.57; p = 0.022). There was a positive correlation between fibulin-1 and central pulse pressure (r = 0.44; p = 0.011) and central augmentation pressure (r = 0.55; p = 0.001). In a multivariable regression model, diabetes, creatinine, fibrinogen and central augmentation pressure were independent predictors of plasma fibulin-1.

CONCLUSION

Increased plasma fibulin-1 levels were associated with diabetes and impaired kidney function. Furthermore, fibulin-1 levels were associated with hemodynamic cardiovascular risk markers. Fibulin-1 is a candidate in the pathogenesis of cardiovascular disease observed in chronic kidney disease and diabetes.

Aortic Augmentation Index is Independently Associated With N-Terminal Pro B-type Natriuretic Peptide in Patients With Peripheral Arterial Disease

Objectives:

To investigate the relationship of aortic augmentation index (AIx) with N-terminal pro B-type natriuretic peptide (NTproBNP) plasma levels in patients with peripheral arterial disease (PAD) with normal left ventricular (LV) function.

Methods:

Totally, 31 patients (23 males, mean age 65 ± 7.4) with a confirmed diagnosis of PAD of the lower limbs (ankle–brachial pressure index [ABPI] <0.90 in at least 1 leg) were enrolled in this study. All patients underwent pulse wave analysis by applanation tonometry of the radial artery using the SphygmoCor system and had a measurement of plasma NTproBNP levels.

Results:

Patients had a mean resting ABPI of 0.62 ± 0.19 and a mean AIx 32.6% ± 6.9. Median (interquartile range) NTproBNP plasma level was 75 (44-210) pg/mL. In a univariate analysis which included age, brachial systolic blood pressure (BSBP), brachial diastolic blood pressure (BDBP), ejection duration index (ED%), heart rate (HR), and NTproBNP, aortic AIx was significantly associated (Spearman rho) with NTproBNP, HR, and ED% ( r = .49, P = .006; r = −.72, P = .000, and r = −.42, P = .02, respectively). Multivariate linear regression analysis showed that AIx was associated with NTproBNP (β = 0.38, P = .02) independent of gender, HR, ED%, and use of β-blockers. N-terminal pro B-type natriuretic peptide explained 8% of the variance in aortic AIx, whereas HR explained 15% of the variance.

Conclusion:

In patients with PAD with normal LV systolic function, AIx is independently associated with NTproBNP. Structural changes in the myocardium might occur due to increased LV afterload as a result of increased wave reflections and arterial stiffness due to atherosclerosis leading to an increase in NTproBNP plasma levels.

Arterial stiffness, its assessment, prognostic value, and implications for treatment

Arterial stiffness has been known as a sign of cardiovascular risk since the 19th century. Despite this, accurate measurement and clinical utility have only emerged in recent times. Arterial stiffness and its hemodynamic consequences are now established as predictors of adverse cardiovascular outcome. They are easily and reliably measured using a range of noninvasive techniques, which can be used readily by risk assessment facilities or individual practitioners. The techniques described in this review are based on the pulsatility of the cardiovascular system, utilizing the timing of pulse travel along major arteries and the magnitude of wave reflection. These have enabled better understanding of the ill effects of arterial stiffening, not only on large arteries and the left ventricle, but also on tiny arteries in highly perfused organs such as brain and kidneys. Treatment options, which directly target the consequences of arterial stiffening, as opposed to arbitrary reduction of brachial blood pressure, have proved clinical superiority; optimal therapy entails use of angiotensin-converting enzyme inhibitors, angiotensin-receptor blockers, and calcium-channel blockers, as well as vasodilating β-blockers. Arterial stiffness will undoubtedly contribute to cardiovascular assessment and management in future clinical practice. Reviews such as this will hopefully increase awareness of the mounting evidence underlying this transition, and the relevant theory and methodology. As we begin the second decade of the 21st century, we are finally collectively coming to realize what pioneers such as Osler, Roy, Bramwell and Hill foresaw in the 19th and 20th centuries.

Noninvasive Evaluation of Left Ventricular Afterload

The mechanical load imposed by the systemic circulation to the left ventricle is an important determinant of normal and abnormal cardiovascular function. Left ventricular afterload is determined by complex time-varying phenomena, which affect pressure and flow patterns generated by the pumping ventricle. Left ventricular afterload is best described in terms of pressure-flow relations, allowing for quantification of various components of load using simplified biomechanical models of the circulation, with great potential for mechanistic understanding of the role of central hemodynamics in cardiovascular disease and the effects of therapeutic interventions. In the second part of this tutorial, we review analytic methods used to characterize left ventricular afterload, including analyses of central arterial pressure-flow relations and windkessel modeling (pressure-volume relations). Conceptual descriptions of various models and methods are emphasized over mathematical ones. Our review is aimed at helping researchers and clinicians obtain and interpret results from analyses of left ventricular afterload in clinical and epidemiological settings.