Gastric Emptying: in Vivo Studies in Healthy Volunteers

After the ingestion and subsequent passage of solid or liquid material into the stomach, the gastric contents will undergo gastric emptying from the stomach into the intestine. The rate of gastric emptying can be very variable and will depend on the presence of gastric pathology or defect, composition and volume of the gastric contents and may even be influenced by factors such as gender and reproductive status. Gastric motility disorders such as gastroparesis and dumping syndrome can affect the rate of gastric emptying and thus warrant the quantitative assessment of emptying. Gastroparesis is a disorder of the stomach characterised by delayed gastric emptying in the absence of any mechanical obstruction and can be further categorised based on severity; mild gastroparesis (where symptoms can be easily controlled), compensated gastroparesis (partial control with use of medication and dietary adjustments) and gastric failure (symptoms are not controllable). Dumping syndrome occurs as a result of rapid gastric emptying which is usually associated with hypermotility of the stomach. It manifests as either early or late dumping syndrome, both of which have distinct physiological bases and clinical presentations.

Typical symptoms of delayed emptying include nausea, vomiting, abdominal pain and abdominal fullness after eating whilst diarrhoea, weakness and light headedness after meal times are common symptoms of rapid emptying. In the Nuclear Medicine department at City Hospital (Birmingham), patients referred for imaging are usually diabetics suffering from feelings of bloatedness after eating and occasional vomiting. Most patients studied are clinically diagnosed with gastroparesis associated with diabetes (where the vagus nerve responsible for controlling movement of food through the digestive tract stops functioning). Dumping is rarely reported as there is an effective tablet treatment for the disorder that usually eases the symptoms. (This includes octreotide therapies which can exert an effect through various mechanisms such as delaying transit, inhibiting the release of gut peptides and impaired fluid secretion). If left untreated gastroparesis can make diabetes worse by making it more difficult to manage blood glucose. Assessment of gastric emptying rate is therefore an important part of diagnosis.

Gastric emptying scintigraphy is a non-invasive diagnostic tool that is used in Nuclear Medicine to study the emptying of contents into the stomach. This form of scintigraphic examination is reproducible, simple to perform, accurate, quantitative and exposes the patient to only a very small radiation dose. It has been significantly optimised and refined over the years and is now well established as the standard method for evaluating gastric emptying. As the 'gold standard' gastric emptying scintigraphy is usually the first stage of the diagnostic journey for a patient, although some may have had a prior endoscopy (usually in cases of severe vomiting).

The procedure is known to vary between institutions, however will usually involve binding of a radiotracer to a solid or liquid meal which is then administered orally. This is followed by positioning of the patient in front of a camera and continuous or intermittent imaging is performed. Data is acquired over a length of time (usually 1-2 hours) and the data subsequently analysed to determine the half emptying time (i.e. the time required for the stomach to empty 50% of the ingested meal) which is then compared to established normal ranges (i.e. normal emptying rate expected for healthy individual). The current radioactive meal used for the study consisting of mashed potato, peas and Beanfeast (soya mince) is not particularly palatable, does not meet the dietary requirements of some patients (e.g. gluten/wheat free) and is difficult to prepare. In addition, in-house in vitro studies have found the current meal to be inferior to other meal preparations. Subjecting the radioactive meal to simulated conditions of the stomach has found that the radiolabel retention was significantly better in other meals such as scrambled egg and porridge.