Ingestible acoustic sensor measures vital signs from within GI tract
The sensor could make it easier to assess trauma patients, monitor soldiers in battle, perform long-term evaluation of patients with chronic illnesses, or improve training for professional and amateur athletes. The new sensor calculates heart and breathing rates from the distinctive sound waves produced by the beating of the heart and the inhalation and exhalation of the lungs.
"Through characterization of the acoustic wave, recorded from different parts of the GI tract, we found that we could measure both heart rate and respiratory rate with good accuracy," says Giovanni Traverso, a research affiliate at MIT’s Koch Institute for Integrative Cancer Research and a gastroenterologist at Massachusetts General Hospital.
Inspired by existing ingestible devices that can measure body temperature, and others that take internal digestive-tract images, the researchers set out to design a sensor that would measure heart and respiratory rate, as well as temperature, from inside the digestive tract. The simplest way to achieve this, the scientists decided, would be to listen to the body using a small microphone.
The researchers essentially created "an extremely tiny stethoscope that you can swallow," says Albert Swiston, a technical staff member at Lincoln Laboratory. "Using the same sensor, we can collect both your heart sounds and your lung sounds. That’s one of the advantages of our approach – we can use one sensor to get two pieces of information."
To translate the acoustic data into heart and breathing rates, the researchers had to devise signal processing systems that distinguish the sounds produced by the heart and lungs from each other, as well as from background noise produced by the digestive tract and other parts of the body. The entire sensor is about the size of a multivitamin pill and consists of a tiny microphone packaged in a silicone capsule, along with electronics that process the sound and wirelessly send radio signals to an external receiver, with a range of about three meters.
In tests along the GI tract of pigs, the researchers found that the device could accurately pick up heart rate and respiratory rate, even when conditions such as the amount of food being digested were varied.
"The [researchers] introduce some interesting and radically different approaches to wearable physiological status monitors, in which the devices are not worn on the skin or on clothing, but instead reside, in a transient fashion, inside the gastrointestinal tract. The resulting capabilities provide a powerful complement to those found in wearable technologies as traditionally conceived," says John Rogers, a professor of materials science and engineering at the University of Illinois, who was not part of the research team.
The researchers expect that the device would remain in the digestive tract for only a day or two, so for longer-term monitoring, patients would swallow new capsules as needed. For the military, this kind of ingestible device could be useful for monitoring soldiers for fatigue, dehydration, tachycardia, or shock, the researchers say. When combined with a temperature sensor, it could also detect hypothermia, hyperthermia, or fever from infections.
In the future, the researchers plan to design sensors that could diagnose heart conditions such as abnormal heart rhythms (arrhythmias), or breathing problems including emphysema or asthma. Currently doctors require patients to wear a harness (Holter) monitor for up to a week to detect such problems, but these often fail to produce a diagnosis because patients are uncomfortable wearing them 24 hours a day.
"If you could ingest a device that would listen for those pathological sounds, rather than wearing an electrical monitor, that would improve patient compliance," Swiston says.
The researchers also hope to create sensors that would not only diagnose a problem but also deliver a drug to treat it.
"We hope that one day we’re able to detect certain molecules or a pathogen and then deliver an antibiotic, for example," says Traverso. "This development provides the foundation for that kind of system down the line."
For more, see the paper published in the journal PLOS: Physiologic Status Monitoring via the Gastrointestinal Tract.