Abstract
Spirometers are medical devices that diagnose and monitor respiratory diseases from forced breathing manoeuvres in patients. It has recently been highlighted in the US and UK that spirometers are not always able to detect or monitor certain respiratory diseases, recommending that more accurate and more sensitive spirometers need to be developed. This coincides with a proposal from clinical researchers to find alternative modes to forced breathing manoeuvres for clinical observations. One potential solution to each of these demands is the development of a highly sensitive and highly accurate flowmeter, the RMK device, designed to measure rested breathing. Five multidisciplinary studies were undertaken to explore the measurement uncertainty (studies 1 to 3) and measurement capabilities (studies 4 & 5) of the RMK device as a potential spirometer. Study 1 investigated accuracy and repeatability, study 2 investigated validity and study 3 investigated stability of the RMK device, each against spirometry measurement standards. The findings across these studies were that the RMK device has a full-scale error of 0.25%, meets repeatability and validity requirements and can maintain accuracy under different flow conditions. Study 4 examined if the RMK device can distinguish between tidal breathing from an asthma cohort and control cohort in the time and frequency domain. These results found that in the time domain the RMK device can identify breathing characteristics that significantly differ between cohorts, but frequency domain results were less conclusive. Finally, study 5 investigated signals detected at low frequency (< 2Hz) from tidal breathing, observing them to be heart rate, which also with correlated with systolic blood pressure. The overall findings of this thesis support that the RMK device is the most accurate device designed for spirometry with potentially new diagnostic and monitoring capabilities. Furthermore, it has demonstrated that tidal breathing can offer clinical insights, so the use of forced breathing manoeuvres might not always be required in spirometry. These results were only possible with a more sensitive and accurate spirometer.