Embedded sensor provides real time respiratory rate

Researchers in Canada have created a smart T-shirt that monitors the wearer's respiratory rate in real time, an advance that could help diagnose or monitor a range of conditions.

The T-shirt - developed at Université Laval's Faculty of Science and Engineering and its Centre for Optics, Photonics, and Lasers – could lead to the manufacture of clothing that could be used to diagnose respiratory illnesses or monitor people suffering from asthma, sleep apnea, or chronic obstructive pulmonary disease.

The smart T-shirt works without any wires, electrodes, or sensors attached to the user's body, said Younes Messaddeq, the professor who led the team that developed the technology which is described in Sensors.

"The T shirt is really comfortable and doesn't inhibit the subject's natural movements,” said Prof Messaddeq. “Our tests show that the data captured by the shirt is reliable, whether the user is lying down, sitting, standing, or moving around."

According to the University, the key to the smart T-shirt is a spiral antenna sewn in at chest level that is made of a hollow optical fibre coated with a thin layer of silver on its inner surface. The fibre’s exterior surface is covered in a polymer that protects it against the environment.

"The antenna does double duty, sensing and transmitting the signals created by respiratory movements," said Messaddeq. "The data can be sent to the user's smartphone or a nearby computer."

As the wearer breathes in, the smart fibre senses the increase in thorax circumference and the volume of air in the lungs, said Messaddeq. "These changes modify some of the resonant frequency of the antenna. That's why the T-shirt doesn't need to be tight or in direct contact with the wearer's skin. The oscillations that occur with each breath are enough for the fibre to sense the user's respiratory rate."

According the paper, the typical measured frequency shift for the deep and shallow breathing was found to be in the range 120–200 MHz and 10–15 MHz, respectively.

To assess the durability of their invention, the researchers put a T-shirt equipped with an antenna through wash cycles. "After 20 washes, the antenna had withstood the water and detergent and was still in good working condition," said Messaddeq.

The paper - Wearable Contactless Respiration Sensor Based on Multi-Material Fibers Integrated into Textile - is available in Sensors.