Making sense of highly-disturbed blood flow dynamics

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The way blood flows in the body (hemodynamics) is widely thought to have a big impact on vascular diseases like atherosclerosis and aneurysms, the leading causes of heart attacks and strokes. Unfortunately, the complex hemodynamics associated with these diseases are difficult to measure directly, which has led to increasing use of computer simulations of blood flow tied to medical images of the patient, something we call image-based computational fluid dynamics (CFD). In the last five years my team and I have uncovered strong evidence that hemodynamics may be more complex that many doctors and engineers think. Textbooks tell us that blood flow is mostly orderly (laminar), and only rarely chaotic (turbulent), which has allowed us to take convenient shortcuts to speed up CFD simulations. By not taking these shortcuts, we have found that high-frequency flow fluctuations can arise during parts of the heartbeat, and may or may not look the same in the next beat. While turbulent blood flow is known to aggravate the cells that make up vessel walls and blood, it remains unclear whether these not-quite-turbulent pulsatile flows, which we term “highly disturbed”, are equally troublesome. To understand that, we must first shed some light on the nature of these flows, which are not well studied because they fall between the laminar and turbulent flows that engineers usually deal with. This is the main goal of my proposed NSERC Discovery research. First, we will figure out how to visualize these highly time-varying, three-dimensional (so, four dimensional) flows, and to quantify their relative complexity. Because we expect these flows to be so visually complicated, we will also use sound to take advantage of humans' ability to discriminate frequencies better by ear than by eye. Second, because highly-disturbed flows are likely to be sensitive to uncertainties in the patient data that drives image-based CFD, we will use clever techniques to determine just how confident we can be in our CFD predictions. Third, because the shape of blood vessels plays a major role in determining the hemodynamics within, we will see if, in light of those uncertainties, we can predict with at least the same confidence the likelihood of highly disturbed blood flow from vessel shape alone, potentially avoiding the need for CFD in the clinic. This basic engineering research will be carried out in parallel to my clinical research with Toronto Western Hospital on hemodynamic factors for predicting brain aneurysm rupture, providing us with the wide variety of patient data needed to meet our objectives. Ultimately, the knowledge we gain will have application to other cardiovascular diseases where highly-disturbed flows are now also being uncovered, and will provide doctors and engineers with clearer guidelines on how to adequately simulate and/or anticipate them.