Brandon Travis

The winner of the best oral presentation at EMBEC'02 (YIC).
Topic: Cardiovascular Mechanics.

My name is Brandon Travis. I started my chemical engineering education at North Carolina State University with the idea of becoming a medical doctor. I discovered that I enjoyed engineering as much as medicine, and decided to enrol as an engineering graduate student at the Georgia Institute of Technology. There, I performed in vitro research in cardiovascular fluid mechanics under the guidance of Ajit Yoganathan. I was lucky enough to receive an International Research Fellowship from the US National Science Foundation to continue my research at Skejby Sygehus in Århus, Denmark. I am currently performing this work in collaboration with Hans Nygaard, an electrical engineer, and Michael Hasenkam, an experimental surgeon.

My research focuses on mechanical prosthetic heart valves. Such valves are quite durable, but tend to predispose patients to thromboembolic disorders, and patients with these valves must undergo lifelong anticoagulation therapy. The reason for this is currently unknown, but there is evidence to suggest that it is caused by leakage across the valve when the valve is in the closed position. This leakage is initiated by a large pressure gradient, and forces blood through small openings between valve parts. Such blood is exposed to high viscous stresses during passage through these gaps and high turbulent stresses within the resulting jets. Previous studies have found that the turbulent stresses created by mechanical prosthesis leakage flow are much higher than those occurring in either the natural circulation or in forward flow across the prosthesis. However, all these studies have been performed in vitro, using a Newtonian fluid to simulate blood flow through small gaps, and large, rigid approximations to the chambers of the heart. These gross simplifications could invalidate the results. The aim of my research is to quantify the turbulent stresses of prosthetic valve leakage in vivo.

To accomplish this, I have designed a traversing apparatus that allows the precise positioning of a small ultrasound transducer with respect to a valvular prosthesis. In my experiments, this device is sewn to a bileaflet mechanical prosthesis and implanted in the mitral position of a pig (see photo). The ultrasound transducer is used to measure leakage velocity over an area just upstream of the valve. Ventricular and atrial pressures are measured simultaneously to allow the calculation of the instantaneous pressure difference that drives the flow. Turbulent stresses can be calculated from the velocity measurements. Preliminary analysis of results from several designs, suggest that the largest turbulent stresses measured in vivo are similar to those measured in vitro, but that this turbulence dissipates very quickly due to jet impingement on chamber walls. Future experiments will determine the effects of leakage gap width and exercise on turbulence during leakage flow.

I hope soon, to use the knowledge I have gained from my experiences at Georgia Tech and Skejby Sygehus to develop my own laboratory and team of scientists in applying the techniques of cardiovascular fluid mechanics to solve current clinical problems. For the present however, I am enjoying analysing the results of my experiments, biking and skating along the coast of the Baltic Ocean, and sampling the delicious pastries that can be found in Danish bakeries!

Brandon Travis
Dept. of Cardiothoracic and Vascular Surgery, Skejby Sygehus, Arhus University Hospital, Denmark
brandontravis2001@yahoo.com