Design, implementation and testing of an implantable impedance-based feedback-controlled neural gastric stimulator

Abstract

Functional neural gastrointestinal electrical stimulation (NGES) is a methodology of gastric electrical stimulation that can be applied as a possible treatment for disorders such as obesity and gastroparesis. NGES is capable of generating strong lumen-occluding local contractions that can produce retrograde or antegrade movement of gastric content. A feedback-controlled implantable NGES system has been designed, implemented and tested both in laboratory conditions and in an acute animal setting. The feedback system, based on gastric tissue impedance change, is aimed at reducing battery energy requirements and managing the phenomenon of gastric tissue accommodation. Acute animal testing was undertaken in four mongrel dogs (2 M, 2 F, weight 25.53 ± 7.3 kg) that underwent subserosal two-channel electrode implantation. Three force transducers sutured serosally along the gastric axis and a wireless signal acquisition system were utilized to record stimulation-generated contractions and tissue impedance variations respectively. Mechanically induced contractions in the stomach were utilized to indirectly generate a tissue impedance change that was detected by the feedback system. Results showed that increasing or decreasing impedance changes were detected by the implantable stimulator and that therapy can be triggered as a result. The implantable feedback system brings NGES one step closer to long term treatment of burdening gastric motility disorders in humans.

Enhanced electrogastrography: A realistic way to salvage a promise that was never kept?

“…Oscillator: Previous literature demonstrated that 50 kHz is an optimal frequency for luminal electrical impedance measurements to minimize interference with regular muscle, nerve, and organ functions, while enabling effective transmission through the body[26,27]. Body conduction of small low frequency signals has been clinically proven to be safe, and has found application in other GI related technologies[29].…”

“…It has been already discussed that the intrinsic gastric electrical oscillator is a complex, multicomponent and dynamic phenomenon, whose relationship with actual gastric motility is so multifaceted that plain EGG cannot reliably assess it. Thus, we recently proposed to enhance an ingestible pill containing a temporary, controllable pseudobezoar with a miniature electronic oscillator of known and strong enough emitting frequency, optimized for good transluminal transmission[26-28]. This is a way to essentially enhance the intrinsic gastric electrical oscillator with a strong, simple, single-frequency source, which could be easily detected cutaneously by traditional EGG equipment and can be consequently processed by the same signal processing tools that plain EGG testing of today employs.…”

In Situ Measurement of Tissue Impedance Using an Inductive Coupling Interface Circuit

“…The improvement lasted for more than one week and the threshold became 5.82 g on day 14. In the second PRF stimulation on day 14, the threshold was still improved but reached a high of 9.08 g on day 15. The efficacy decreased and the effective period became short.…”

“…The is equal to the reflected resistance defined in (15). From (13), the input reactance is also mixed with the reactance of .…”

“…The feedback of bio-impedance can form a closed-loop system for implanted devices, especially for implantable micro-stimulators. A micro-stimulator that is integrated with a bio-impedance sensor can apply the electrical stimulation voltage according to the feedback impedance [15]. For pacemakers, the bio-impedance-based stimulation technique has been proposed to adjust automatically the intensity of the stimulus or to select the correct stimulating electrode that maintains a comfortable and effective stimulation therapy [16].…”