1. .
Jamie Nunez1,2,3, Olga Yakovenko3, Wendy Thomas3
1Summer Undergraduate Research Program 2015, 2GenOM Project
3Department of Bioengineering, University of Washington, Seattle, WA
Methods
Background
Acknowledgements: This research was made possible thanks to the
National Institute of Health (1R01 AI106987-01), NASA Space Grant,
LSAMP, the University of Washington GenOM Project (NIH
5R25HG007153-03), a gracious donation from Drs. Anne Dinning and
Michael Wolf, and the Genentech Foundation.
Results
Effect of Flow on Bacterial Endocarditis
Bacterial endocarditis is an infection on the inner lining of the
heart. Even though this disease has been studied for decades, a
reliable, non-invasive treatment is still not available. Our research is
aimed toward creating a device that mimics the conditions involved
in this disease. Once created, this device can then be used to better
understand bacterial endocarditis and potentially test new
treatments. We hypothesize that flow conditions play a critical role
in the initiation and progression of bacterial endocarditis. In the
heart, flow is pulsatile, meaning that the flow oscillates between two
different flow rates. In order to test our idea, we first started with a
parallel flow chamber and ensured that we can get a response time
low enough to mimic the human heart. Once this was complete, we
measured the amount of bacteria binding in different pulsatile
conditions. This showed that bacteria bound at slightly higher rates
in pulsatile conditions until about 1 Pa. In the future, we will further
decrease our time constant and repeat our experiment with S.
gordonii to confirm and further investigate our conclusion.
Flow Chamber Set Up: A set up enables bacteria to be input into the
flow chamber and out into a waste collector. The bottom of the flow
chamber is covered in a monolayer of ligand that the bacteria being
studied can attach to (shown above).
Programmable Pump: A pump outputs constant flow and pulsatile
flow for a certain amount of time with the correct programming.
Particle Imaging Velocimetry: Beads with a known radius are input
into the flow chamber and imaged in video. These videos can then be
used to calculate the shear stress actually present within the flow
chamber.
Inlet Outlet
Figure 2: Flow region within current flow chamber
Bacteria Ligand
Figure 1: Vegetations
formed on the mitral valve
caused by bacterial
endocarditis.
Sources: (left) www.e-heart.org,
(top) www.scripps.org
Our Approach
• Preliminary studies: enable our current device to accurately reproduce
the pulsatile flow found within the heart.
• Design and assembly: based on the results achieved with the current
model, create a device that introduces biochemical conditions and
other flow conditions found in the heart.
What is bacterial endocarditis?
• A disease where the inner lining of the heart
becomes inflamed due to a bacterial
infection.
• Often associated with patients who have
defective heart valves.
• On average, 3.6 out of 100,000 people per
year are reported to have this disease.
(Moreillon, Philippe. "Infective
Endocarditis." Lancet 363 (2004): 139-49.
Web.)
Abstract
Graph A & B: Bead Experiments
• Experimental results closely follow simulation
• Slight overshoot in some cases
• Reproducible data since the time constant is the same from day to day.
• A time response of ~0.15 seconds is desired.
• A rate of 60 bpm is desired but can not be done currently due to the slow
response time.
• We can assume the time response is approximate to 0.3 s during
experiments with the same set up.
• With a frequency = 15 bps, we can assume the flow is dropping
close to zero during times where there is no flow input.
• When we do experiments with bacteria, we will be able to predict
what the shear stress truly is inside the flow chamber at any given
point.
• Bacteria bind at slightly higher rates in pulsatile vs. constant flow
Conclusion
Sources: (left) guardianlv.com, (top)
www.clipartpanda.com
Future Work
Figure 4: Simulations vs. experimental results. (a) The response time was assumed to be 0.3 seconds and, as seen in the figures to the left, the experiment
confirmed this response time. (b) Example of the pace of a normal heart beat and the importance of the time response. (c) Data from an experiment on
10/20/2015 showing the number of S. gordonii binding under pulsatile and constant flow at different shear stresses.
0%
20%
40%
60%
80%
100%
120%
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5
PercentageofBacteriaBoundComparedtoPeak
Flow
Shear Stress (Pa)
S. gordonii Binding in Pulsatile and Constant Flow
Pulsatile
Constant
Negative Controls
0%
20%
40%
60%
80%
100%
120%
140%
160%
0.00 2.00 4.00 6.00 8.00 10.00
PercentofVelocityatMaxFlowRate
Time (s)
Pulsatile Flow with 15 bpm
Day 1 Experimental Response
Day 2 Experimental Response
Predicted Response
a) b)
0%
20%
40%
60%
80%
100%
120%
1.00 2.00 3.00 4.00
PercentofVelocityatMaxFlowRate
Time (s)
Pulsatile Flow with 60 bpm
Experimental Response
τ = 0.15 sec
τ = 0.3 sec
c)
• A lower response time is needed to more closely simulate
physiological conditions. This can be done by using shorter, stiffer
tubing or possibly a stiffer gasket, or other various techniques.
• Repeat S. gordonii experiment with current device to confirm results.
• Repeat bead experiments with the new device to measure its time
response.
Graph C: S. gordonii Experiment
• Pulsatile flow shows the same trend as constant flow, though the amount of
bacteria bound at each condition is slightly higher.
• Negative controls show same amount of non-specific binding at low and
high shear conditions.