Cardiovascular Engineering
Gabriella Glomp
Undergraduate Student Researcher
Vanderbilt University
Evanston, Illinois, United States
Patients struggling with organ failure, post-operative recovery, severe trauma, or infection can benefit from the life-saving therapy known as Extracorporeal Membrane Oxygenation (ECMO) — a system comprising a mechanical blood pump and an oxygenator (Figure 1), creating an external support system. Current ECMO systems, however, present a set of limitations when it comes to facilitating seamless and efficient patient care. Patients can remain on ECMO from days to weeks as a bridge to recovery or to lung transplant. During this time, a patient’s health status and metabolic needs constantly change, requiring manual adjustments of operational settings, to regulate the amount of blood flow and gas flow. Current ECMO systems are bulky in size, which presents challenges in mobilizing patients, during physical therapies or interhospital transports.
Our group is developing an improved, more durable ECMO system to reduce manual operations, improve ergonomics and biocompatibility, allow for mobility, and, eventually, for use outside the hospital. My project focuses on the pump. Specifically, I am developing a blood pump system that can be flexibly modified and programmed to modulate these settings. Here, I present the initial prototype for a pump console that operates a clinical centrifugal blood pump at clinically relevant flow and pressure for ECMO. The console operates in both constant and pulsatile flow modes. Ultimately, this novel pump system will be able to respond to rapidly changing physiological signals and modulate blood flow, in order to maintain relative homeostasis as the patient lives dynamically, without constant supervision of physicians.
The current clinical pump consoles have poor flexibility in terms of modifying their designs to meet my specific research needs. As such, my first step was to design and build a platform to operate a clinical centrifugal pump without relying on an existing clinical system. Our design utilizes a magnetic disc drive, directly attached to a DC motor, which can be programmed and operated with an Arduino mega and a motor driver. Clinical centrifugal blood pumps for ECMO used here (LivaNova Revolution) can be driven in a contactless manner, using this magnetic drive. To achieve an optimal alignment between the magnetic disc and the pump, an enclosure was first designed and built, such that the motor and magnetic disc drive would remain in place, secured within a laser-cut wood structure. The enclosure's top panel, where the pump head is secured, is designed to be replaceable, allowing for compatibility with any magnetically driven centrifugal pump head. The enclosed LivaNova pump’s hydraulic performance was then evaluated in both water and blood flow loop circuits. The pump was run at 6, 9, or 12 volts, and the pump outlet was progressively occluded to increase the pressure head. Pressure head, circuit flow, rotational speed, and motor current and voltage were acquired to quantitatively evaluate pump performance. Lastly, pulsatile flow and pressure were induced using pulse-width modulation (PWM) on an Arduino mega (Figure 5).
We have developed and prototyped a programmable pump that can circulate blood in both continuous and pulsatile manners. Preliminary testing suggests the pump can produce clinically relevant levels of flow and pressure for ECMO. The configuration demonstrated an ability to generate pressure upwards of 250 mmHg and flow within the target range of 4-6 LPM while operating between 500 and 3000 RPM (Figure 4), sufficient for clinical ECMO circuits [3-4]. Our programmable prototype is versatile and theoretically compatible with any magnetically driven centrifugal pump. This blood pump platform could be implemented as a low-cost research tool in various applications in which blood flow is titratable to patient status. Using this platform, researchers can experiment with various methods of speed, flow, and pressure modulation. Pulsatility in extracorporeal circulation has been an intriguing, much-debated concept; yet little data exists to prove its benefits over constant flow, in terms of improving end-organ perfusion, reducing clot burden inside the oxygenator, and improving gas transfer rates [1-2]. Costing less than two hundred dollars, our console provides a low-cost platform, to investigate these potential benefits of pulsatility in ECMO. Other future directions include testing and implementation of a feedback system, such that the pump modulates flow to maintain homeostasis. This portable and adaptive pump, as envisioned and designed, meets the needs of both patients and physicians within the ECMO field, to achieve our goals of a cost-effective strategy to adaptively meet patient’s physiological needs and improve quality of life.
Vanderbilt Wond'Ry for their support
Anderson Meat for blood supply for circuit testing
Vanderbilt Undergraduate Summer Research Program for funds used in these studies
The faculty mentor (Rei Ukita) received financial support from the Vanderbilt Faculty Research Scholar program.