Breath gas analysis
Respiratory gas analysis is the scientific study of human breath. The goal is on the one hand to identify markers that allow to draw conclusions on the clinical condition of a patient, and also to develop mathematical models which allow to convert from the respiratory gas concentration to the corresponding blood concentrations. The findings can then be implemented in respiratory gas tests for medical diagnosis.
In contrast to the decrease in blood samples of breathing gas for the patient sample is non-invasive and can be repeated as often as desired. Breath samples can be analyzed in real time and therefore also allow for continuous monitoring of changes in body substances, for example, on the ergometer, in a sleep laboratory or in intensive care.
Could previously only substances in high concentrations such as Carbon dioxide and alcohol are identified, it is by the progress made in recent years in the analysis technique (GC -MS, PTR -MS, SIFT -MS, IMS, chemical sensors ) is possible, a single molecule in a trillion molecules ( ppt) to discover.
History
The modern era of the respiratory gas analysis was initiated by the Nobel Prize winner Linus Pauling, who showed that human breath more than 200 volatile organic compounds (volatile organic compounds, VOCs ) in picomolar concentration.
Context Atemgas-/Blutkonzentrationen
A simple model for the relation between respiratory gas and blood concentrations was reported by Farhi:
Here, the alveolar concentration (assuming that they coincide with the measured ), the mixed venous concentration, and the blood: . Partition coefficient air and the ventilation-perfusion ratio (at rest about 1 )
Multiplying the average concentration of acetone is obtained by a factor of 3 different values of the actually measured arterial blood values which are, for example, according to this equation in the end- tidal breath air with the partition coefficients in the range of. For isoprene with a partition coefficient of the ventilation-perfusion ratio in this equation can no longer be neglected.
Further developments of this model are therefore an active field of research