Influence of respiratory variables on the on-line detection of exhaled trace gases by PTR-MS.

BACKGROUND: Modern gas analysis techniques permit real time and on-line quantification of multiple volatile trace gases within a single exhalation. However, the influence of various respiratory manoeuvres affecting exhalation flow and the kinetics of metabolite release to the gas-phase remain largely unknown.
METHODS: We examined variation in the concentrations of selected trace gases over a range of expiratory flows (50; 100; 250 ml/s) and after 30 second periods of breathold and paced hyperventilation. On-line measurement of breath samples from healthy volunteers (n=10) was performed by proton transfer mass spectrometry.
RESULTS: Exhaled acetone increased with higher expiratory flow rate (805, 838, 898 ppb, p=0.02). Levels of methanol (206 vs 179 ppb, p<0.01), acetaldehyde (26 vs 22 ppb, p<0.01), ethanol (410 vs 208 ppb, p=0.01) and dimethyl sulphide (113 vs 103 ncps, p<0.01) fell significantly following 30s hyperventilation. After 30 second breathold levels of methanol (206 vs 217 ppb, p=0.02), acetone (805 vs 869 ppb, p<0.01), isoprene (348 vs 390 ppb, p=0.02) and dimethyl sulphide (113 vs 136 ncps, p=0.02) increased significantly. Variation in respiratory parameters did not significantly alters the level of acetonitrile, propanol and butyric acid within the breath of healthy subjects.
CONCLUSIONS: These findings demonstrate that respiratory manoeuvres significantly influence the measured concentration of a number of exhaled VOCs that are of potential importance within the clinical setting. Our results support the adoption of standardised practices for breath gas analysis by on-line and real time mass spectrometry methods.