Breath sampling control for medical application

Abstract

Sampling of breath under human control or automated control with sensors was combined with chemical determination of a synthetic sample using multi-capillary column ion mobility spectrometry to measure quantitative variability. Variation was 19% with an automated inlet and 33% with human control. Sensors to operate an automated inlet were also evaluated with human subjects and included carbon dioxide (CO2), flow (direction and velocity), volume (integrated from the flow rate) and humidity, all operating in the mainstream of exhaled air. The flow sensor provided a measure of sampling of breath from the upper airways and other sensors gauged exclusive sampling of the end-tidal volume as well. Sensors for volume and CO2 exhibited identical profiles, using appropriate threshold values, in reference to inspiration and expiration. A sensor for humidity lagged inspiration and expiration with a delay of 300 ms and therefore is diminished in value. The sensors recommended for an automated inlet for breath sampling are CO2 and the exhaled or tidal volume though tidal volume varies significantly with personal physiognomy. This necessitates an evaluation of a subject to establish a threshold setting and CO2 is the single best parameter providing the availability of sensor signal within 50 ms.