Hemodynamics

Hemodynamics

Amanda Buck had just started her postdoc job, and already the disconnect was palpable. As a bioengineer trained in vascular biology, she focused on hemodynamics, using computational fluid dynamics to analyze how blood moves through arteries. She thought about blood flow the way oil company engineers think of petroleum flow through pipelines—focusing on where in the artery it’s moving fastest, where it’s slow, how much pressure it’s under, and where it eddies. The results of such calculations can help reveal how diseases progress and whether medical devices either function or fail.

But Buck was now working mostly with brain-imaging experts, who used the same term differently. To them, hemodynamics referred to proxy measurements of brain activity that are obtained using specialized magnetic resonance imaging (MRI) methods. Researchers typically ask a person to carry out a task, such as solving a math problem or identifying a particular smell, and measure how much blood rushes into specific parts of the brain, or how much oxygen that blood was carrying. The equations were different from engineering, the units were different, and the ideas were different.

“It was frustrating at first,” Buck recalls. “I had no idea what they were talking about.”

If she had been collaborating with a cardiologist, hemodynamics would have meant something different still. In that medical specialty, hemodynamics—literally, the dynamics of blood—refer to parameters that gauge how well a patient’s heart and circulatory system are working. One such parameter, the ejection fraction, is the fraction of the blood by volume that gets pumped out of the heart’s left ventricle, which does the lion’s share of the work of sending blood out to the body. A healthy heart will eject 65 percent of the blood, but a diseased heart might eject only 35 percent. Other hemodynamic parameters gauge blood pressure in different parts of the heart or in the body’s major arteries, levels of oxygen or carbon dioxide in the blood, or how much these parameters vary.