Abstract
Selected ion flow tube mass spectrometry, SIFT-MS, has been used to measure simultaneously the concentrations in exhaled breath of ethanol, acetaldehyde, ammonia, acetone and, routinely, water vapour, following the ingestion of various amounts of ethanol in 500 ml of water. These breath analyses were obtained from only single exhalations, the results being available immediately in real time. The breath ethanol reaches concentrations that are only approximately consistent with its dilution in blood and body water. For moderate ethanol doses the decay quickly exhibits first-order kinetics (a single exponential decay) whereas for relatively large ethanol doses, the initial decay of ethanol from the breath is slow, indicating saturation kinetics. For smaller doses, and following a meal, the breath ethanol increases only slightly indicating that it is largely metabolized in the stomach. We suggest that the time delay (following ethanol ingestion) before the breath ethanol begins to increase is an indicator of the gastric emptying rate. Then the rate of decay of ethanol from the breath/blood is related to its rate of metabolism subsequent to its dispersal into the body water. The much lower breath acetaldehyde levels correlate well with the ethanol levels indicating that it is mostly formed from the metabolism of the ethanol. The breath ammonia is seen to 'dip' following the water/alcohol drink and this is consistent with previous work in which this same phenomenon was observed following the ingestion of comparable volumes of liquid meals. The simultaneous breath acetone concentrations increase somewhat with time as is expected during the fasting state. The water vapour measurements are indicators of the precision and accuracy of the breath analyses, these being sufficient to show the differences between the breath (body) temperatures of the individuals of less than 1 °C. This study demonstrates the potential of SIFT-MS for non-invasive physiological measurement.