Researchers at the University of Massachusetts Amherst have engineered physiological-sensing textiles that can be created into sleep clothing they have dubbed "phyjamas." These phyjamas contain unobtrusive, portable devices for monitoring heart rate and respiratory rhythm during sleep.
The special pajamas were created by graduate students Ali Kiaghadi and S. Zohreh Homayounfar, with their professors Trisha L. Andrew, a materials chemist, and computer scientist Deepak Ganesan.
"The challenge we faced was how to obtain useful signals without changing the aesthetics or feel of the textile. Generally, people assume that smart textiles refer to tightly worn clothing that has various sensors embedded in it for measuring physiological and physical signals, but this is clearly not a solution for everyday clothing and, in particular, sleepwear," Andrew said.
"Our insight was that even though sleepwear is worn loosely, there are several parts of such a textile that are pressed against the body due to our posture and contact with external surfaces. This includes pressure exerted by the torso against a chair or bed, pressure when the arm rests on the side of the body while sleeping, and light pressure from a blanket over the sleepwear," Ganesan added.
"Such pressured regions of the textile are potential locations where we can measure ballistic movements caused by heartbeats and breathing," he explained, "and these can be used to extract physiological variables."
To make their vision of phyjamas a reality, Andrew, Ganesan and colleagues had to engineer many innovations. Since there was no existing fabric-based method to sense continuous and dynamic changes in pressure, they came up with a new fabric-based pressure sensor.
They then combined the new sensor with a triboelectric sensor to develop a distributed sensor suite that could be integrated into loose-fitting clothing like pajamas. To fuse signals from many points, they further developed specialized data analytics.
Several user studies
To test their new phyjamas, the team undertook several user studies and found that the novel wearables can extract heartbeat peaks with high accuracy, breathing rate with less than one beat per minute error, and perfectly predict sleep posture.
"We expect that these advances can be particularly useful for monitoring elderly patients, many of whom suffer from sleep disorders," said Andrew. "Current generation wearables, like smartwatches, are not ideal for this population since elderly individuals often forget to consistently wear or are resistant to wearing additional devices, while sleepwear is already a normal part of their daily life. More than that, your watch can't tell you which position you sleep in, and whether your sleep posture is affecting your sleep quality; our Phyjama can."