Swallowable electronic capsules can provide gas profiles of the gut and distinguish changes in a person’s diet.
A visit to a physician typically begins with the measurement of your body temperature, blood pressure, heart rate and respiratory rate. These vital sign measurements are a powerful indicator of general health and are quick, inexpensive and easy to acquire. Future routine medical care could soon be complemented by an additional layer of measurements thanks to the development of ingestible electronic capsules (Fig. 1). Ingestible electronics, which are also known as swallowables, have distinct advantages over the wearables currently used to obtain traditional vitals. In particular, they are not limited by the skin barrier and can be immersed in the environment of the gut, the site of chemical exchange with the body. Swallowables are especially useful for measuring vitals when traditional measurement techniques are not feasible or practical, such as during intense physical activity1. Moreover, swallowables have access to the ordinarily hidden gut microbiome, whose connection to both health and disease is just beginning to be understood2.
The gut microbiome is the community of microorganisms that live in the human gastrointestinal system and may play a role in the development of a startling number of diseases, including inflammatory bowel disease, obesity, cardiovascular disease, circulatory disease and even autism3. Just as body temperature is an indicator of general health, the concentration of gases produced by the microbiome is an indicator of gut health4. More valuable still is an understanding of the gas concentration profile along the entire length of the gut. For example, a healthy individual will have different gas concentrations in the stomach, small intestine and colon, and it is currently very difficult to accurately and noninvasively measure gut gas at specific locations. Because the diagnostic value of these measurements is so high, researchers have gone to great lengths to acquire the gas profile data. Current measurement techniques include analysis of flatus, insertion of tubes, whole-body calorimetry and breath tests. These techniques are, however, invasive, inconvenient or highly unreliable. Furthermore, although gas at the entrance and exit of the gut can be monitored, the small bowel, and particularly the middle of the small bowel, is largely inaccessible. Writing in Nature Electronics, Kourosh Kalantar-Zadeh, Peter Gibson and colleagues now show that gas concentration profiles along the length of the human gut can be measured using a small swallowable electronic capsule5.
The researchers — who are based at RMIT University, Monash University and CSIRO Agriculture and Food in Australia — created devices that were packaged in untethered capsules that were 26 mm long with a diameter of 10 mm, and contained gas concentration and temperature sensors, a microcontroller, a radio-frequency transmitter and batteries. The gas sensors have membranes that selectively allow gases through, while excluding liquids. In this pilot study, small pocket-sized receivers were worn by volunteers, and the gas concentration data was transmitted from the capsule every five minutes as the device travelled the length of the gut. The sensors could measure oxidizing reagents, hydrogen and carbon dioxide, which resulted in concentration profiles of the gases as a function of time.
This is the first human pilot trial of such capsules, and Kalantar-Zadeh and colleagues were able to obtain data in which gas profiles from high- and low-fibre diets were compared. A rudimentary understanding that gas profiles can be altered by modulating diet has previously been obtained via faecal analysis6. However, through their gas analysis and capsule transit times, the researchers were able to clearly differentiate between the two diets, which is not possible with traditional faecal analysis. Fermentation patterns of individuals were also detectable using the capsules, which opens up the exciting possibility of monitoring a person’s response to a custom diet. We know that diet can be customized to modulate the microbiome, but in order to effectively design functional foods, feedback is needed to close the loop between a prescription and its effects — the gas-sensing capsule could provide the required link. Another notable outcome of the work was that the gas profiles can approximately identify the location of the capsule and therefore provide a means of measuring the transit times of contents through the stomach and the small and large intestine. This is important for applications unrelated to the microbiome such as capsule endoscopy for gastrointestinal surgery.
The gas-sensing capsules, and swallowables in general, have remarkable potential to help us understand the functional aspects of the gut microbiome, its response to dietary changes and its impact on health. The devices could also help deliver the concept of an individualized diet by providing a monitoring and feedback system. As the size and cost of electronics continues to decrease, it might not be too long before a routine healthcare visit involves a check of your vital signs and a request to swallow a tiny electronic monitoring device.