May 4, 2023 | The first-ever wearable sensor for monitoring muscle atrophy has been developed by researchers at The Ohio State University thanks to an interest in the muscle-shrinking condition by NASA, which has been funding most of the work to date. This means that one day patients could start independently tracking their muscle mass and strength rather than going to the doctor’s office for an MRI or to have a flexible tape measure wrapped around multiple body parts, according to Allyanna Rice, graduate fellow in electrical and computer engineering.
A new study published recently in IEEE Transactions on Biomedical Engineering (DOI: 10.1109/TBME.2023.3248959), where Rice was the lead author, describes the proposed electromagnetic sensor constructed of conductive “e-threads'” that run along a stretchable fabric in a zigzag pattern. The prototype device, tested on a model of a calf muscle, also employs two coils for transmitting and receiving signals.
A bulky network analyzer was used to make measurements, so the team will need to implement a smaller circuit board before the system is truly wearable and human-based experiments can be run to see how it works on actual patients, says Rice. The sensor could be readily applied to other limbs or body parts since the underlying technology would stay the same. “It’s just [a matter of] adjusting the size of the sensor so that it stretches similarly but conforms nicely to the limb.”
The major study finding was that the sensor could measure small-scale volume changes in overall limb size and monitor muscle loss of up to 51%, which is “kind of overkill,” she says. “You don’t expect astronauts or anyone on earth to really lose that much muscle—I believe around 30% is the maximum seen at NASA. However, [the agency] doesn’t really know what’s going to happen when it sends people up [to Mars] for two years or more.”
Accommodating such a big change in muscle mass also means “the sensor would fit a large portion of the population, in terms of overall circumference, in this case of the calf,” says Rice. It could be a one-size-fits-all device for people large and small.
This is still early-stage research, she stresses, but the long-term goal is to bring the sensor into clinical use at a time scale suited to patients’ underlying health condition, she continues. For patients in hospital intensive care units who might quickly lose muscle, the device might be used to monitor changes daily. On the other hand, older patients might use it weekly or monthly at home and, ideally, send the data directly to their doctor through an app or some other interface to enable their treatment plans to be personalized.
Muscle atrophy has a variety of causes but is most typically a side effect of degenerative disease, aging, or muscle disuse. The gold standard for obtaining a super-accurate measurement of muscle density and composition as well as size is an MRI, Rice says, but frequent testing can be time-consuming and costly.
In primary care settings, the more commonly employed method is simply to measure limb circumference, she adds. A medical professional is needed because those measurements need to be done consistently over time and at the right location on limbs. “Our sensor could be scaled to ... get all those measurements all at once instead of having to use a tape measure 15 different times.”
The novel sensor, which resembles a blood pressure cuff, is the first big work to emerge from Rice’s fellowship from NASA to support her graduate school studies. Muscle atrophy is one of the biggest effects on the body when it is subjected to the microgravity environment for long periods of time, she says in explaining the rationale for the study.
To simulate the calf tissue of an average-sized person, researchers fabricated 3D-printed limb molds filled with ground beef, which has similar electrical properties to the human body, explains Rice. Ground beef is also easy to mold into different shapes, making it a “good first approximation” to use even if it is notoriously unpleasant to handle. Commercially available, mannequin-type leg phantoms also have the properties of human tissue but are constant in size.
In the future, the conductive thread-based sensor could be one of multiple sensors populating a wearable sleeve for detecting and monitoring all sorts of health issues at the same time, says Rice. The needs of astronauts are top of mind, given the funding source, but a combined-use device of that sort would be useful for patients everywhere.