The challenge: developing a realistic, reliable, and reconfigurable testing environment to advance and improve a novel heart assist device without the need for animal testing.
A couple years ago, David Keeling and colleagues from the University of Leeds designed the Intelligent Ventricular Assist Device (iVAD) -- an implantable mesh ‘jacket’ that will wrap a failing heart and rhythmically contract to help it beat.
Horizontal bands in the jacket are attached to the spindles of miniature motors that wind and unwind to tighten and relax the bands. The heart-circling bands must be tightened in a precise sequence that coordinates with the organ’s varying natural rhythms, IEEE Spectrum explains.
Usually, these sorts of things would be tested on an artificial circulatory system or on animal test subjects. But this team wanted to avoid both approaches.
They needed some rig that simulates the heart while also monitoring the iVAD’s assistance. Specifically, it must be capable of mimicking the movement of hearts in various conditions of health and must react realistically when assistance is applied from the compressive bands.
To assess their device, they came up with a ‘hardware-in-the-loop’ iVAD heart simulator: a metal heart that reproduces the mechanical characteristics of a beating heart, along with a circulatory blood flow model (pictured above).
- Their mechanical heart is a spring cage hooked up to two linear actuators -- one on the right side and one on the left -- to flex the ‘heart’ walls and mimic the alternating strokes of the right and left ventricles.
- They model the blood flow as an electrical network. Each of the 6 blood-holding compartments in the model is characterized by pressure, vessel compliance, and flow inertia.
- Modifying each of these parameters allows them to simulate a wide range of conditions to mimic both disease and good health.
- Pressure sensors arrayed around the mechanical organ measure the pressure exerted by the iVAD bands and feed the data into a controller that checks the blood-flow model and directs the linear actuators to modify the shape of the heart accordingly.
Many cardiac assistance devices and artificial hearts require contact with the patient’s blood supply (which can lead to inflammatory and clotting problems) and lead lines for the power supply that protrude through the skin (which can be a source of infection). The iVAD doesn’t contact the blood, and its miniature motors can be powered non-invasively.
The iVAD heart simulator won design awards at the National Instruments’ Week earlier this month: best Life Sciences application, the Humanitarian Award, and they even took home the (best-in-show) 2012 Application of the Year Award.
[Via IEEE Spectrum]
Images: University of Leeds