Abstract
Using selected ion flow tube-mass spectrometry (SIFT-MS) for on-line analysis, we aimed to define the optimal single-exhalation breathing manoeuvre from which a measure of expired acetone concentration could be obtained. Using known acetone concentrations in vitro, we determined the instrument's accuracy, inter-measurement variability and dynamic response time. Further, we determined the effects of expiratory flow and volume on acetone concentration in the breath of 12 volunteers and calculated intra-individual coefficients of variation (CVs). At acetone concentrations of 600-3000 ppb on 30 days over 2 months there was an instrument measurement bias of 8% that did not change over time, inter-day and intra-day CVs were 5.6% and 0.0%, respectively, and the 10-90% response time was 500 +/- 50 ms (mean +/- SE). Acetone concentrations at exhalation flows of 193 +/- 18 (mean +/- SD) and 313 +/- 32 ml s(-1) were 619 +/- 1.83 (geometric mean +/- logSD) and 618 +/- 1.82 ppb in the fraction 70-85% by volume of exhaled vital capacity (V70-85%) and 636 +/- 1.82 (geometric mean +/- logSD) and 631 +/- 1.83 ppb in V85-100%. A difference was observed between acetone concentrations in the V70-85% and V85-100% fractions (p < 0.01), but flow had no effect. Median intra-individual CVs were 1.6-2.6%. On-line SIFT-MS measurement of acetone concentration in a single exhalation requires control of exhaled volume but not flow, and yields low intra-individual CVs and is potentially useful in approximating blood glucose and monitoring metabolic stress.