Breath sampling control for medical application

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.