Intracardiac Turbines Suitable for Catheter-Based Implantation-An Approach to Power Battery and Leadless Cardiac Pacemakers?

OBJECTIVE: Cardiac pacemakers are powered by batteries, which become exhausted after a few years. This is a problem in particular for leadless pacemakers as they are difficult to explant. Thus, autonomous devices powered by energy harvesters are desired. METHODS: We developed an energy harvester for endocardial implantation. The device contains a microgenerator to convert a flexible turbine runner's rotation into electrical energy. The turbine runner is driven by the intracardiac blood flow; a magnetic coupling allows hermetical sealing. The energy harvester has a volume of 0.34 cm3 and a weight of 1.3 g. Computational simulations were performed to assess the hemodynamic impact of the implant. The device was studied on a mock circulation and an in vivo trial was performed in a domestic pig. RESULTS: In this article, we show that an energy harvester with a 2-bladed 14-mm-diameter turbine runner delivers 10.2 ± 4.8 µW under realistic conditions (heart rate 80/min, stroke volume 75 ml) on the bench. An increased output power (>80 µW) and power density (237.1 µW/cm3) can be achieved by higher stroke volumes, increased heart rates, or larger turbine runners. The device was successfully implanted in vivo. CONCLUSION: The device is the first flow-based energy harvester suitable for catheter-based implantation and provides enough energy to power a leadless pacemaker. SIGNIFICANCE: The high power density, the small volume, and the flexible turbine runner blades facilitate the integration of the energy harvester in a pacemaker. This would allow overcoming the need for batteries in leadless pacemakers.

Modeling the effect of tilting, passive leg exercise, and functional electrical stimulation on the human cardiovascular system.

Long periods of bed rest negatively affect the human body organs, notably the cardiovascular system. To avert these negative effects and promote functional recovery in patients dealing with prolonged bed rest, the goal is to mobilize them as early as possible while controlling and stabilizing their cardiovascular system. A robotic tilt table allows early mobilization by modulating body inclination, automated passive leg exercise, and the intensity of functional electrical stimulation applied to leg muscles (inputs). These inputs are used to control the cardiovascular variables heart rate (HR), and systolic and diastolic blood pressures (sBP, dBP) (outputs). To enhance the design of the closed-loop cardiovascular biofeedback controller, we investigated a subject-specific multi-input multi-output (MIMO) black-box model describing the relationship between the inputs and outputs. For identification of the linear part of the system, two popular linear model structures-the autoregressive model with exogenous input and the output error model-are examined and compared. The estimation algorithm is tested in simulation and then used in four study protocols with ten healthy participants to estimate transfer functions of HR, sBP and dBP to the inputs. The results show that only the HR transfer functions to inclination input can explain the variance in the data to a reasonable extent (on average 69.8%). As in the other input types, the responses are nonlinear; the models are either not reliable or explain only a negligible amount of the observed variance. Analysis of both, the nonlinearities and the occasionally occurring zero-crossings, is necessary before designing an appropriate MIMO controller for mobilization of bedridden patients.