Development of an Inlet Pressure Sensor for Control in a Left Ventricular Assist Device

Abstract

A Tesla type continuous flow left ventricular assist device (VAD) has been designed by Penn State and Advanced Bionics, Inc. (ABI). When a continuous flow device is employed, care must be taken to limit low pressures in the ventricle that can produce an obstruction to the inlet cannula or trigger arrhythmias. Design of an inexpensive, semi-conductor strain gage inlet pressure sensor to detect suction has been completed. The research and design analysis included finite element modeling of the sensing region. Sensitivity, step-response, temperature dependence and hysteresis tests have been performed on prototype units. All sensors were able to withstand the maximum expected strain of 82 μin/in at 500 mmHg internal pressure. Average sensitivity was 0.52 ±0.24 μV/mmHg with 0.5 V excitation (n=5 units). Step response time for a 0 to 90 mmHg step change averaged 22 milliseconds. Hysteresis was measured by applying and holding 75mmHg internal pressure for 4 hours, followed by a zero pressure measurement, and ranged from -15 mmHg to 4.1 mmHg (n=3 units). Offset drift varied between 180 and -140 mmHg over a four week period. (n=2 units). Span temperature sensitivity ranged from 18 to -21 μV/°C (n=5 units). Gain temperature sensitivity ranged from -7.4 to 4.9 μV/°C (n=5 units). With the inherent drift, it is currently not possible to use the transducer to measure actual pressures, but it can easily be used to measure pressure changes throughout the cardiac cycle. This signal can then be used in the control system to avoid ventricular suction events.

Management of ventricular arrhythmias in patients with ventricular assist devices

“…Moving forward, additional studies relating the clinical occurrence of ventricular arrhythmias to molecular and physiological shifts within the myocardium will be invaluable in better defining which mechanisms are most strongly implicated in the time-dependent risks of ventricular arrhythmias in VAD-supported hearts. Further device evolution, including inflow cannula modifications [19,63] and inlet pressure control systems that adjust rotor speeds and prevent suction [23,[64][65][66], may reduce the incidence of ventricular arrhythmias among VAD-supported patients. Prospective trials assessing the benefits of de-novo prophylactic ICD placement and the need to replace ICDs in patients free of post-VAD ventricular arrhythmias would be particularly welcome.…”

An implantable Fabry-Pérot pressure sensor fabricated on left ventricular assist device for heart failure

“…A direct measure of left ventricular pressure (LVP) would obviate the need for many of the assumptions required in indirect methods, and is the motivation for development of an inlet pressure sensor. An integrated pressure sensor at the inlet of the continuous flow LVAD would provide a direct measure of left ventricular function during mechanical support (Bullister et al 2002;Fritz et al 2010). By actively sensing the LV pressure using the inlet pressure sensor, a control algorithm can be developed to optimize LVAD pump speed.…”

Rotary blood pump control using integrated inlet pressure sensor

“…The proposed control system uses inlet pressure to assess ventricular loading. A pressure sensor that can be integrated to the the inlet of a continuous flow LVAD has been developed by our group and tested in vitro and in vivo [12]. Semiconductor strain gages were bonded to a thinned diaphragm region on a titanium shell creating a seamless blood interface to the pump inlet for maximum biocompatibility.…”