Measuring device (100) for analyzing a sample gas by means of infrared absorption spectroscopy, which has: - a measuring chamber (2) with the sample gas to be analyzed, - a laser (1), which is arranged with respect to the measuring chamber (2) such that light emitted by the laser passes through the measuring chamber (2), - a detection device (61) that detects the light emitted by the laser (1) and that it passes through the measuring chamber (2) and - an evaluation unit (8) that evaluates the signals generated by the detection device (61) with respect to a light absorption that takes place in the measuring chamber (2), in where - the laser (1) is a narrow band emission laser, whose line width is less than or equal to the width of an infrared absorption line to be measured from the sample gas and is less than 0.2 cm- 1, wherein - the laser (1) is designed and configured in such a way that the frequency of l Laser is periodically varied within a defined spectral range, the laser frequency and its variation being selected such that at least one infrared absorption line to be measured from the sample gas is in the defined spectral range, and where - The detection device (61) is designed and configured in such a way that it detects the light emitted by the laser (1) and that passes through the measurement chamber (2) with temporal resolution such that the light absorption can be determined within the defined spectral range with frequency resolution, characterized in that the detection device (61) is designed and configured to detect, in the defined spectral range, a plurality of measurement points, corresponding in each case to an individual absorption measurement, and to carry out each individual absorption measurement within 10-5 s or faster, and why the measuring device ( 100) is suitable and is configured to, as a sample gas, measure the respiratory gas of a human being or an animal, the measuring device (100) presenting an open structure without valves, which could
