In 1997 I learned that vortex rings had been observed in the human heart, and what that might mean for improving diagnoses. Since then, I’ve been fascinated with trying to get a better view of cardiac fluid dynamics, and a better understanding of the possible implications for, well, helping sick people. Who could resist?
By analyzing the fluid mechanics of the heart and great vessels, we can better understand normal and pathologic function, leading to improved diagnostics and treatment. I have been working in experimental fluid mechanics since my PhD. My focus is on shear flows and the resulting vortex dynamics. Initially I studied applications in combustion; ramjets, rockets, and gas turbine engines, using flow visualization techniques that included laser-based diagnostics such as particle image velocimetry (PIV) and laser Doppler anemometry. In 1997 I learned (thank you Robin Shandas) that the physics of three-dimensional unsteady shear and vortex dynamics are also important in the cardiac ventricles and great vessels. The formation mechanism sounded a lot like the unsteady combustion fluid dynamics I’d been studying up to that point. Since then a large fraction of my research has been in this area, primarily in developing diagnostics and analysis techniques such as Echo PIV and 4DMRI.
Currently I’m working on data supplied by National Jewish Health and the Veterans Administration with CU Anschutz. NJ is known for its focus on the pulmonary (lungs) issues. They get a lot of patients with pulmonary hypertension (PHT), high blood pressure in the arteries leading from the right side of the heart to the lungs. PHT is important because the right ventricle can’t pump into high pressure forever; eventually it will fail. So, it’s important to measure the pressure in the pulmonary artery system, but those arteries are a bit hard to get at; you can’t put a blood pressure cuff around them. To diagnose PHT you either have snake a pressure sensing catheter into the pulmonary artery (from the neck or groin) or infer the pressure from other hopefully noninvasive types of measurements. There are a variety of measurements based on echocardiography, but the catheter is still the gold standard.
That’s where the vortex ring in the right ventricle comes in. Vortex rings rotate around toroidal (donut-shaped) cores of fluid with vorticity. Vorticity is a derivative quantity, so it will be sensitive to changes in the fluid dynamics. Our hypothesis is that the progression of a disease like PHT will show up as a change in the vorticity of the fluid in the heart early in the disease. We can determine the vorticity using 4DMRI, aka 4DCMR, which shows us the 3 dimensional, 3 component velocity field of blood flow in the heart, reasonably resolved in time. From that we can compute the vorticity field. This measurement is non-invasive, and it’s non-ionizing, unlike an x-ray. The downside is that these scans take 45 minutes or more, and they are expensive, around $1000. Plus the resolution in time, space and velocity are marginal for this type of analysis, so we have to be careful how we interpret the data.
The VA data is for a slightly different purpose. Diabetes is a huge issue in the veteran population, as well as in the population at large, in both men and women. People with diabetes don’t get the same cardiovascular health gain from exercise as people without diabetes, so we are helping analyze data from diabetes patients and controls to see how the flow in the heart is different before and after an exercise intervention, in the hopes of unraveling this mystery.