Respiratory rate monitoring devices for the acute care setting: device development and evaluation

Respiratory rate is an important vital sign because it changes early in acute illness. In acute care settings such as emergency departments, respiratory rate is measured manually but this method has shortcomings. Accordingly, technological solutions to this problem are sought.

A novel system of classification of respiratory rate measuring devices was developed and a review of the literature was undertaken. Microelectronic mechanical sensor (MEMS) accelerometer and gyroscope devices were identified as having potential for further development. Literature gaps regarding the performance of MEMS gyroscopes in measuring respiratory rate were identified. MEMS devices detect chest wall movement from which respiratory rate can be measured.

Device trials were conducted with healthy volunteers and MEMS accelerometers (N = 34) and gyroscopes (N=36) had their respiratory rate measurement performance compared with that of a reference device, a chest mounted strain gauge. Sensors were mounted at different sites on the body wall to determine optimum site of placement. Measurements were made in the supine and seated positions to investigate effects of posture on measurements.

No statistically significant difference was found between respiratory rates measured at any site in either posture. MEMS accelerometers were found to have a mean absolute error (MAE) of between 0.73 and 2.23 bpm in the seated posture and 0.43 and 1.32 bpm in the supine posture. MEMS gyroscopes were found to have an MAE of 0.34 – 1.20 bpm seated and 0.45 – 0.82 bpm in the supine posture.

Attempts were made to improve accuracy of these measurements by means of developing statistical signal quality indices but these were found to be ineffective, whereas some of these are noted in the literature to be effective for electrocardiogram and photoplethysmogram signals.

It is concluded that MEMS accelerometers and gyroscopes can be used in devices to measure respiratory rate but further technical improvements must be sought.