The invention relates to a measurement device and to a method for analyzing a sample gas by infrared absorption spectroscopy. The measurement device comprises: a measurement chamber (2) with the sample gas to be analyzed, a laser (1) being arranged in relation to the measurement chamber (2) such that the light emitted from the laser radiates through the measurement chamber (2), a detection device (61) detecting the light being emitted from the laser (1) and radiated through the measurement chamber (2), and an evaluation unit (8) evaluating signals generated by the detection device (61) regarding a light absorption occurred in the measurement chamber (2). Provision is made that the laser (1) is a narrowband emitting laser, the line width of which is smaller or equal to the width of an infrared absorption line to be measured of the sample gas, the laser (1) is designed and arranged such that the laser frequency is varied periodically within a defined spectral range, wherein the laser frequency and its variation are chosen such that at least one infrared absorption line to be measured of the sample gas lies in the defined spectral range, and the detection device (61) is desigen and arranged such that it detects the light being emitted from the laser (1) and radiated through the measurement chamber (2) in such a time-resolved manner that the light absorption can be determined frequency-resolved within the defined spectral range, wherein the detection device (61) carries out a single absorption measurement within 10- 5 s or faster. Furthermore, the measurement device is suited and can be arranged to measure the respiratory gas of a human or animal as sample gas, wherein the respiratory gas exchanges in the measurement chamber only by the respiration of the human or animal, and the respiratory resistance of the measurement device is less than 60 mbar.
