The effects of the herbal preparation, STW5-II, on proximal gastric relaxation in healthy volunteers.

This trial will observe the physiological gastrointestinal responses to a single dose (20 drops, 1.1 ml) of STW5-II, vs placebo, to investigate the mechanisms by which this herbal preparation may exert its gastrointestinal symptom relieving effects. Two study visits, separated by at least four days, are required. Each visit will take approximately four hours. Participants will receive, in randomised, double-blind fashion, oral administration of either (i) 20 drops (1.1ml) of STW5-II or (ii) 20 drops (1.1ml) control solution (i.e. containing no active ingredients). For both study visits, participants will fast for ~14 hrs overnight, and abstain from alcohol and vigorous exercise for 24 hrs prior to each visit. On each study day, participants will attend the Clinical Research Facility, Adelaide Medical School, Adelaide Health and Medical Sciences (AHMS) Building at 8:30am. Upon arrival, the participant will be intubated with an orogastric catheter. The catheter will be a double-lumen polyvinyl tube (outer diameter: 3.5 mm), which has a flaccid, thin-walled, compliant polyethylene bag (max. capacity 1200 ml) tied onto and tightly wrapped around its distal end. The catheter will be connected to a barostat device, which consists of a strain-gauge linked by an electronic relay to an air aspiration / injection system. The barostat device measures changes in gastric volume at a fixed pressure. Thus, when the gastric wall relaxes, air is injected into the bag to maintain the pressure, whereas air is withdrawn when the stomach contracts. The catheter will be inserted through the mouth and the bag positioned in the fundus of the stomach by inflating it with ~300-400 ml of air, carefully pulling it back until its passage is restricted by the lower oesophageal sphincter and then pushing it back in again by 3 cm. The minimal distending pressure (MDP) will then be determined by gradually increasing intragastric pressure in 1 mmHg steps. The MDP is defined as the intrabag pressure which first results in a bag volume of 30 ml air and is necessary to overcome the intra-abdominal pressure. Intra-bag pressure will then be set at 2 mmHg above the MDP and baseline intragastric pressure will be monitored until it is stable for 10 min. Following this, participants will ingest 50 ml of water with either (i) STW5-II or (ii) control solution (as stated previously). Complete ingestion of 50 ml of water and STW5-II or placebo will be confirmed by the investigator. Gastric relaxation (i.e. the volume increase in the bag at the set pressure) in response to the treatment will be recorded for 180 min. The participant will be asked to complete a VAS questionnaire to assess GI symptoms (e.g. fullness, nausea, bloating) at baseline, and then at 15-min intervals. These scales consist of a horizontal line, 100 mm long, on which the participant places a vertical mark across the line, indicating the strength of each symptom felt at that time, with 0 mm indicating that the symptom is not felt and 100 mm that the symptom is extremely strong. At 180 min, the catheter will be removed, and the participant offered a light lunch after which they will be free to leave the laboratory.