The antrum is the lower part of the stomach and the duodenum is the first part of the small intestine, which is connected to the stomach. Antroduodenal manometry is used to study how the stomach and the first part of the small intestine are working. It can be used to measure both the strength and coordination of muscle contractions of the stomach and small intestine. To do this test, a small flexible tube (catheter) is passed through the nose, down the esophagus, through the stomach, and into the small intestine. The tube is passed after the child is sedated, but the manometry test itself is done after the child wakes up, often the next day. If the child has a gastrostomy tube, the catheter will be passed through the gastrostomy instead of through the nose.