A technical setup for ECG-controlled stimulation of the n. vagus

Introduction:

Stimulation of the n. vagus is getting more important for treatment of cardiovascular diseases [1]. An optimal stimulation should take changes of for example ECG, blood pressure or PTT into account. Therefore we present a modular technical concept, which successfully meets such requirements for a controlled stimulation.

Material and Methods:

In order to face all demands several parts are pivotal. For the invasive part electrodes and electronics and for wireless and non-invasive monitoring systems for pulse and ECG are necessary. Additionally all monitored parameters have to be processed and the PTT as an important cardiovascular parameter has to be calculated by an external unit, which is interacting bidirectionally with the stimulator.

Results:

For the acquisition of ECG textile-integrated dry-surface electrodes based on medically approved silicone are used. Such electrodes are filled with conductive particles, which lead to similar electrical properties as commercial available Ag/AgCl electrodes [2]. In combination with a communication network on the basis of a microcontroller MSP430F2013 and a telemetric chip MG2455 an autarkic monitoring system is realized [3]. Recorded signals are processed in the microcontroller after the AD-converting and transferred using ZigBee 2.4 GHz-band standards (sampling rate 250Hz and over sampling of 64). The preamplifier records the single channel ECG based on an instrument amplifier AD627 and a band rejection filter for 50Hz noise. The uniqueness of the technical setup is a smart interaction of dry-surface electrode setup with an ultra flexible invasive electrode system.

The ultra flexible electrodes are based on polyimide and micro-machined by photolithographic processes (see details in [4]). Most commonly such electrodes are implanted by surrounding the n. vagus (cuff-electrode) or being implanted longitudinal-intrafascicularly (tf-LIFE). The application has a direct influence on the design and selectivity of the stimulation. Therefore all electrodes are specially adjusted depending on application and location of implantation. All electrodes are characterized by means of impedance spectroscopy, resulting into low and suitable impedance and an extreme high reproducibility of the fabrication process. Finally a complete evaluation referring to EN ISO 10993 standards is carried out proving the biocompatibility for single components [5].

Discussion:

Summarizing we presented a high reproducibility and electronical stability of two electrode systems as well as the smart communication for a controlled stimulation. Furthermore we proofed the biocompatibility of each component proving the suitability medical use. Further validation of biocompatibility and extended tests of the functionality of the complete system will be performed in the nearby future.

References:

[1] Rozman, J. et al. Selective Stimulation of Autonomic Nerves and Recording of ENG in a Canine Model, Artif. Organs, 32 (8), 2008

[2] BMBF project Seed, 16SV3533

[3] Hoffmann, K.-P. et al., Flexible dry surface-electrodes for ECG long-term monitoring, 29th Ann. IEEE EMBS Conf., 2007

[4] Hoffmann, K.-P. et al. New technologies in manufacturing of different implantable microelectrodes as an interface to the peripheral nervous system, 1st IEEE/RAS EMBS BioRob, 2006

[5] Steltenkamp, S. et al. Electrode structures for acquisition and neural stimulation controlling the cardiovascular system, 31st Ann. IEEE EMBS Conf., 2009.