The elucidation of the mechanical characteristics of blood flow is important toward the understanding of cardiovascular physiology and disease. In particular, the stresses that blood flow impose on the surface of cardiovascular structures is known to impact the biology of these structures and regulate cardiovascular health. Unfortunately, the pulsatility of blood flow, its strong interactions with the surrounding vasculature and its turbulent nature make it particularly difficult to study. The MSCBL has pioneered in new tools to quantify the flow in realistic models of normal, diseased or anatomically abnormal cardiovascular structures such as heart valves, ventricles, and blood vessels. Other systems of interest are medical devices and new technologies used in hemodialysis vascular access. The tools developed in the MSCBL have enabled the assessment of blood flow and fluid stresses at high spatial and temporal resolutions, in both idealized and patient-specific geometries. Experimental flow measurements conducted in the MSCBL typically involve the use of a flow loop replicating native blood flow conditions in the laboratory setting, and particle image velocimetry (PIV), an optical technique used to measure flow velocity fields. Computational techniques include the use of computational fluid dynamics (CFD) and fluid-structure interaction (FSI) modeling.
Mechanical forces are powerful regulators of biology and disease. In the vasculature, the expression of particular cellular phenotypes appears to depend not only on a combination of intrinsic genetically programmed biology but also on local hemodynamic environmental factors induced by blood flow. In the spectrum of forces experienced by cardiovascular tissue, one major component is the wall shear stress or friction force exerted by the blood flow on the endothelium. Through dedicated receptors, the endothelial cells lining the surface of cardiovascular structures are able to sense the characteristics of this force and to transduce this mechanical signal into biochemical signals, altering in turn cellular function. Interestingly, while physiologic wall shear stress maintains homeostasis, wall shear stress abnormalities often correlate with disease states. In this context, the elucidation of the cause-and-effect relationships between cardiovascular biology and blood flow has the potential to advance the understanding of disease progression and to enable new diagnosis and treatments. The MSCBL has designed new laboratory tools capable of subjecting native cardiovascular tissue to physiologic mechanical stresses or mechanical signals typically experienced under disease conditions. Those sophisticated devices have demonstrated the ability of blood flow alterations to drive aortic valve calcification, and bicuspid aortic valve disease. Similar tools are being designed to study the potential of blood flow abnormalities as contributors to discrete subaortic stenosis and hemodialysis vascular access patency.
The cardiovascular system consists of the heart, the blood vessels, and the blood. Its function is to transport oxygen, nutrients, hormones, and cellular waste products throughout the body.
The heart is the pump that drives blood flow throughout the cardiovascular system. It weighs about 300 grams and beats 70 times per minute. It pumps about 5 liters of blood every minute. The two ventricles of the heart pump blood to the lungs, and to the different organs and tissues in the body, respectively.
The aortic valve achieves unidirectional blood flow between the left ventricle and the aorta. It normally consists of three leaflets that open during systole and close during diastole, under the pressure difference established between the ventricle and the aorta.
The bicuspid aortic valve is the most common congenital valvular defect and affects 2% of the population. While a normal aortic valve consists of three leaflets, the bicuspid aortic valve forms with only two, as a result of fusion between two adjacent leaflets.
Calcific aortic valve disease is the most common aortic valve disorder. It affects 4% of adults over 65 years of age and consists of the formation of calcific lesions on the valve leaflets.
Discrete subaortic stenosis is a type of constriction that is caused by the presence of a fibrous ring below the aortic valve, anywhere between the aortic valve and the mitral valve. It results in a restricted outflow from the left ventricle into the aorta.
Computational fluid dynamics (CFD) is the science of predicting fluid flow, heat transfer, mass transfer, chemical reactions and related phenomena by solving the mathematical equations which govern these processes using a numerical approach.
Particle image velocimetry (PIV) is an optical method of flow visualization used to obtain instantaneous velocity measurements in a flow field. Tracer particles are used to seed the flow and are illuminated using a laser sheet. The motion of the seeding particles is used to calculate the local flow velocity field.