# Bioelectrical Signals for the Diagnosis and Therapy of Functional Gastrointestinal Disorders
## 3 Stomach
### Therapies  
Gastric electrical stimulation has been proposed as an alternative therapy for gastric motility disorders such as gastroparesis and functional dyspepsia. The overall goal for electrical therapy is to improve gastric motility by enhancing contractions, normalizing propagation, or modulating the function of a sphincter. Electrical stimulation is usually performed by using either short pulses at a high-frequency or long pulses at a low-frequency also known as gastric pacing [83].  
High-frequency electrical stimulation in the GI tract was first trialed by [PERSON] et al. in 1963 to stimulate the stomach and intestine for the treatment of ileus [84]. Later, it was performed on gastroparesis patients for whom the distal corpus and proximal antrum achieved the most effective stimulation response and resulted in symptom relief and improvements in gastric emptying rates [85]. Subsequently, two other studies have performed stimulation using similar techniques on refractory-diabetic or idiopathic gastroparesis subjects, and have shown that over 70% of the subjects reported improvements in symptoms with reduced nausea and vomiting scores, and that 73% of the subjects experienced an improvement in the quality of life [86,87]. Enterra Therapy (Medtronic plc, Minneapolis, MN, USA), is one form of high-frequency stimulation which utilizes an implantable pulse generator.  
The efficacy of Enterra Therapy has been the focus of a number of studies, and two meta-analysis studies reported that high-frequency stimulation significantly improved gastric emptying rates and symptoms [88,89]. However, conflicting findings have been reported by a comprehensive multicenter, randomized controlled trial performed on patients suffering from chronic or refractory vomiting with or without gastroparesis [90]. This study showed that although symptoms were improved (vomiting episodes were reduced in 31% of patients with the stimulation), no observable improvements were reported in gastric emptying rates or quality of life. Enterra Therapy has been shown to not alter or entrain the underlying SW patterns, and the mechanism for symptomatic improvements remains uncertain [91]. It has been proposed that the symptomatic improvements are a result of activation of vagal afferent pathways that influence central nervous system control mechanisms for nausea and vomiting, accompanied by enhanced vagal efferent autonomic function and decreased gastric sensitivity to volume distention [92].  
Gastric pacing and transcutaneous electrical stimulation (TES), unlike high-frequency stimulation, have been applied in a relatively limited number of studies. Two studies have shown that gastric pacing was able to entrain the SW activity in the stomach, which resulted in improved symptoms and accelerated gastric emptying in patients with gastroparesis [93; 94]. More recently, spatio-temporal responses of SWs to different pacing parameters that can potentially guide the therapies were studied in porcine models by integrating with high-resolution SW mapping [95; 96]. However, the lack of implantable devices that can deliver the energy needed for pacing remains a research challenge. Similarly, only two studies have investigated TES in patients with functional dyspepsia, with a 55% reduction in symptom scores reported in one study [97]. Improved dyspeptic symptoms, quality of life, and gastric emptying were reported in the second study when a wearable stimulation device was used [98]. There is a significant need for more controlled studies to identify optimal parameters to reveal the efficacy of both gastric pacing and TES.