The Atmo gas capsule is an ingestible, wireless, gas sensing capsule that is currently being developed and commercialised as a biomarker tool for gastrointestinal disorders. Following ingestion, the Atmo gas capsule transmits information about gases and temperature to an external receiver. The oxygen concentration profiles generated allow the passage of the capsule between aerobic (small intestine) and anaerobic (large intestine) to be characterised. The practical application of the Atmo Capsule is currently limited by the need to validate oxygen concentrations as a marker of position within the gastrointestinal tract. Preliminary studies using intestinal ultrasound have shown that migration of the Atmo capsule from the stomach to the duodenum, and its passage from terminal ileum to caecum, corresponds with major changes in oxygen concentration.

The SmartPill measures pH and offers gold-standard measurements of gastrointestinal transit times. To validate the ability of the Atmo Capsule to measure gastrointestinal transit time, this device will be compared to the SmartPill. This will allow the equivalence of these two devices in gastrointestinal transit measurements to be evaluated.

This study aims to compare gastrointestinal transit times using immediately sequential ingestion of the SmartPill and Atmo capsule in patients with gastrointestinal motility disorders. A total of 60 participants diagnosed with either gastroparesis (n=30) or slow transit constipation (n=30) will be recruited by advertisement (via online support group pages, such as Gastroparesis Australia) and word-of-mouth. Potential participants will be screened for eligibility. Suitable individuals will be sent a Participant Information Sheet and Consent Form for review. Participants will be asked to stop proton pump inhibitors, histamine receptor blockers and antacids 3 days prior to the study and during the study. Medications that affect gastric motility will also be stopped 48 hours before the start of the study and during the study. Following an overnight fast, participants will attend the Macarthur Clinical School, Western Sydney University, where the Principal Investigator (Dr Jerry Zhou) will review the Patient Information Sheet with each participant and obtain informed written consent. Participants will then be asked to consume a cereal bar with 200mL of water. Participants will subsequently ingest the SmartPill and Atmo capsule. The order of swallowing these devices will be randomised with a computer-generated list. Participants will be monitored for 15 minutes post-ingestion. Subjects will then fast for the next 6 hours, after which they will consume their normal meals for the rest of the day. The data receiver for both the SmartPill and Atmo capsule will be worn or kept within 1.5 metres of the body until passage of the capsule has been confirmed by observation in the toilet bowl or signal loss from both capsules after a bowel movement.

Adverse events, bowel movements and the presence of gastrointestinal symptoms will be recorded in a digital diary (as part of the Atmo receiver system) whilst the Atmo capsule is in the body. Once both devices have passed from the body, participants will attend Macarthur Clinical School, where receivers will be returned and an investigator will review the digital diary with them.The investigator will follow up with the participant via phone or email approximately one week after the study to enquire about symptoms and adverse effects.

For the SmartPill, anatomical landmarks will be identified by changes in pH profiles along the gastrointestinal tract as previously reported in the literature. More specifically, gastric emptying time will be defined by the time of capsule ingestion to the presence of a sharp rise in pH (more than three units), where the capsule passes from an acidic environment (pH ≤4) in the stomach to a more basic environment (pH \>6) in the duodenum. Small intestinal transit will be determined by the time between the end of gastric emptying and identification of the ileo-caecal junction (a fall in ≥1 pH unit distal to gastric emptying). Colonic transit time will be defined as the time from ileocaecal junction to exit from the body. Whole gut transit time will be calculated as time of oral ingestion to exit from the body.

For the Atmo capsule, oxygen profiles will be used to characterise gastric emptying, small intestinal and colonic transit. Whole gut transit time will be calculated based on a change in temperature from exiting the body. The primary end-points of this study will be the agreement between gastric emptying, small intestinal and colonic transit times generated by the gas-sensing capsule vs wireless pH-motility. Statistical analysis with linear regression and by degrees of agreement (Bland-Altman tests) of measurements between the two devices will address these end-points. More subjects will be studied pending the results of this pilot study. The results, conduct and reporting of this study will conform to the STARD 2015 guidelines.