Design, Development and Evaluation of a Contactless Respiration Rate Measurement Device Utilising a Self-Heating Thermistor

Respiration rate (RR) is an important vital sign for early detection of health deterioration in critically unwell patients. Its measurement is currently subjective, relying on visual counting of chest movements. The design of a new RR measurement device utilising a self-heating thermistor as its sensing element is described. The thermistor is situated in a hand-held air chamber with a funnel attachment that detects respiratory airflow up to 30 cm from the face. The exhaled respiratory airflow reduces the temperature of the thermistor, and its temperature recovers during inhalation. A microcontroller provides signal processing while its display screen shows the respiratory signal and RR. The device has been evaluated on 27 healthy adult volunteers, mean age 32.8 years (standard deviation 8.6 years). The RR readings from the device were compared with the visual counting of chest movements and the contact method of inductance plethysmography implemented using a commercial device (SOMNOtouch™ RESP). The RR readings from the new device and SOMNOtouch™ RESP, averaged across the 27 participants, were 14.6 breaths per minute (bpm) and 14.0 bpm respectively. The device has a robust operation, is easy to use and gives an objective measure of RR in a non-contact manner.