The bench-top driver system was able to produce pressure differentials near the target performance of up to 10 mmHg in an 80 ml volume, with operating frequencies up to 1.2 Hz, sufficient for a heart rate up to 70 BPM. Future work will evaluate design changes to increase the operating frequency range and pressure generated, and test prototypes connected to cardiac assist devices.

1. Discussion & Conclusions
The bench-top driver system has provided results
showcasing the ability of the system to produce pressure
differentials near target performance, up to 10 mmHg in an
80 ml volume, with operating frequencies up to 1.2 Hz,
sufficient for a heart rate up to 70 BPM.
Future Aims
• Evaluate effects of wireframe structure design, magnet
and plate sizes on device performance
• Utilize modeling techniques and prototyping to increase
range of operating frequencies and device pressure
• Test prototypes by connecting driver’s implantable bellow
to a cardiac assist device to verify performance at nominal
usage, i.e. 20 mmHg with 100 mL displacement for a 300
ms stroke (systole is ~300 ms at 60 bpm)
.
Preliminary Results
References
1. Go, A. S., et al. (2013). Circulation, 127, e6-e245.
2. Moreno, M. R. (2011). Medical Devices, 5(4), 1-9.
3. Bennett, L. E., et al. (2001). Clinical Transplant, 25-40.
Materials and MethodsObjective & Approach (Cont.)
ECG Acquisition/Triggering Program
• A LabVIEW program acquires and processes ECG signals
to generate trigger pulses to power electromagnet and run
driver in synchrony with the heart
• Program capable of auto shutdown in event of abnormal
ECG Signals
• Program allows for automated or full user override of voltage
regulation, QT interval cycle length, specific site of triggering
Electromagnet Control System
• Relay switch with H-bridge configuration actuates
electromagnet with switching polarities to induce repulsion
and attraction alternatively
• Millar pressure catheter transducer used to quantify the
pressure-volume interrelationship between the pressure
differential and bellow fill volume
Figure 3: Schematic of the
electromagnet control
system used in this project
including: Trigger signal,
relay switch circuit with H
bridge configuration, power
supply, electromagnet, Millar
pressure transducer control,
and a PC with LabVIEW
An Implantable Pneumatic Driver with Non-Invasive Transmural Powering
for Cardiac Assist Devices
Sayyeda Saadia Razvi2, José V. Coello3, Steve Zambrano1, John C. Criscione1, Michael R. Moreno1*
Biomedical Engineering, Texas A&M University, College Station, Texas1, Mechanical Engineering, University of Texas, Austin,
Texas2 , Electrical Engineering, Instituto Tecnológico de Mérida, Mérida, Yucatán3Biomedical Engineering
Introduction
• Congenital heart failure (CHF) affects more than 5.3
million people in the U.S. with 550,000 new cases
diagnosed annually
• A mechanical cardiac assist device has been developed
by Moreno et al. (2011) to treat the symptoms of CHF
• At present the device requires a bedside pneumatic driver
with transcutaneous drivelines that have inherent infection
and inflammation risks
• Thus demand exists for a fully implantable, subcutaneous
driver with non invasive transmural electromagnetic
powering to bypass need for transcutaneous drivelines
Objective & Approach
To develop an implantable, non-invasive, pneumatic drive
technology which utilizes above dermal induced magnetic
fields for transcutaneous driving of gaseous-filled bellows.
Implantable Cardiac Assist Driver System
• Bellows are fabricated from Nylon-6 material and are
sealed around two plates, distal and proximal
• The Distal plate (2.2” diameter) houses a neodymium disk
magnet (N52 grade, 1” diameter, 3/8” thick, axially-
magnetized)
Permanent Magnet
Electromagnet
Proximal Plate
Wireframe spring
Bladder
Distal Plate
Connection Port
1. Electromagnet coil is
energized in opposite
polarity
2. Wire frame pushed apart
& expands bellows
3. Spring action induces
vacuum
1. Electromagnet coil is
energized in one polarity
2. Distal plate is pulled
towards proximal and
compresses bellows and
spring
3. Compression action
shuttles gas through port
Figure 2: Computer aided design model of the implantable pneumatic
driver (left), and wireframe diagrams describe compressed (top-right) and
expanded (bottom-right) states
Skin section
Figure 3: LabVIEW program generates square pulse trigger for actuating
relay and powering electromagnet in synchrony with ECG signals
Figure 4: LabVIEW Program recognizes abnormal ECG signals (e.g.
hyperkalemia) and switches off power to device
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
0 1 2 3 4 5 6
ElectricalSignal
Time (s)
ECG Signal Square Wave Trigger
Figure 5: Pressure
measurement data from
bench-top driver with an
80 mL fill volume and
12-wire opposed offset
helix frame at around
1.4Hz
-12
-10
-8
-6
-4
-2
0
2
4
6
8
10
0.5 0.7 0.9 1.1 1.3 1.5 1.7
GagePressure(mmHg)
Height of Distal Plate (in)
Compression
Expansion
Figure 6: Pressure dependence on stroke length of bladder in bench-top
test conducted at nominal frequency of 0.8 Hz. Ideal stroke determined to be
around 1” with current design.
-15
-10
-5
0
5
10
15
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
GagePressure(mmHg)
Frequency (Hz)
Compression
Expansion
Figure 7: Heart rate limit test conducted by modulating switching frequency
of an arbitrary function generator. Stroke length was set at 1” for test
-5
-4
-3
-2
-1
0
1
2
3
4
5
0 1 2 3 4 5 6 7 8
Pressure(mmHg)
Time (s)
www.biomechanicalenvironments.com
Diastole with contrast filled
passive component providing
passive support while preserving
normal cardiac geometry
End-systole with air filled active
component applying uniform
compression via redistribution of
fluid in the passive component
Figure 1: In vivo study
of cardiac assist
device depicting the
relationship between
the saline filled
passive component
and the air filled active
component of the
device
-1
-0.5
0
0.5
1
1.5
0 1 2 3 4 5 6
ScaledAmplitudes
Time (s)
Driver Pressure (Scaled) Trigger Pulse ECG Compression
Expansion