**3.5 Electrogastrography (EGG)**

EGG is a non-invasive technique that measures gastric myoelectric activity- and consequently its function- using skin electrodes placed in the upper abdomen. Normal activity consists of slow waves ad potential spikes (which would correspond to contractions), and the normal frequency is approximately 3 wpm [25].

The correlation between EGG and gastric emptying has been reported in several studies: in patients with functional dyspepsia, 40% of patients showed abnormal EGG [26]. The presence of EGG abnormalities in patients with dyspepsia or delayed gastric emptying, and the presence of motor abnormalities in many patients with GERD, leads to the conclusion that EGG abnormalities can be detected in some patients with gastroesophageal reflux disease, too.

### **3.6 Water Load Test**

The Water Load Test is an economic, non-invasive and easy to perform test, that can be reproduced in healthy subjects as well as in patients with reflux disease or functional dyspepsia [27]. It is useful to assess visceral hypersensitivity, that has been identified as an important pathophysiologic mechanism in patients with functional disorders of the upper gastrointestinal tract [28].

The test consists of having the patient drink as much water as possible, consecutively for 5 minutes (WL5), or until a feeling of satiety is reached. The patients have to complete a visual analogue scale (VAS) in order to objectivate their symptoms before and after the test, and they have to assign a value for each of them, scaled from 0 (absent) to 10 (severe). Then, water is consumed from an unmasked flask that is refilled after each drink, but the patients are blinded as to the actual volume of water consumed. Finally, the total volume of water ingested, and the perceived symptoms are registered and analyzed [29].

There is also evidence that some GERD patients, more often with non-erosive disease, may improve dyspeptic symptoms after acid-suppression therapy [25]; however, large cohort studies suggest that that the reflux patients and dyspeptic patients represent two distinct populations [26]: GERD patients with mild erosive oesophagitis and with non-erosive reflux disease have the WLT abnormal, similar but not identical to that reported in patients with functional dyspepsia [29]. The WLT does not allow a precise determination of visceral hypersensitivity; however, it is worth noting that these findings appear somewhat similar to those described in other studies by means of the barostat technique in dyspeptic patients, although a correlation between these two methods is still not available. Although there is literature evidence suggesting abnormalities of gastric motor and sensory function in GERD patients [30, 31].

#### **3.7 Other tests**

Although these tests were not created exclusively to study gastric function, they are becoming a useful help in order to assess its accommodation in a non-invasive way: ultrasonography, magnetic resonance (MRI) and Single-proton Emission Computed Tomography (SPECT) are some examples.

Ultrasound imaging is a widely available method but offers only an indirect measure of gastric accommodation through antral diameter [17]. On the other hand, MRI is able to provide information about gastric meal emptying, the total volume of gastric contents and also three-dimensional images of the stomach [32].

**Figure 4.**

*(A) Multiple SPECT images are reconstructed with the help of a software system (B) into a three-dimensional image of the stomach (C) for the measurements of gastric volumes [35].*

SPECT is an emerging test that uses intravenous injection of 99mTc-pertechnetate with tomographic imaging (three-dimensional reconstruction) of gastric mucosa. The evaluation of gastric accommodation is completed by measuring gastric volumes in fasting and post-prandial state [33] and by analyzing them with a commercially available software. Mean volumes detected by SPECT are comparable to that of barostat; moreover, it permits simultaneous assessment of gastric emptying and accommodation [34] (**Figure 4**).
