Quantum cascade laser-based integrated cavity output spectroscopy of exhaled nitric oxide

A nitric oxide (NO) sensor employing a thermoelectrically cooled, continuous-wave, distributed feedback quantum cascade laser operating at 5.47 μm (1828 cm^-1) and off-axis integrated cavity output spectroscopy was used to measure NO concentrations in exhaled breath. A minimum measurable concentration (3σ) of 3.6 parts-per-billion by volume (ppbv) of NO with a data-acquisition time of 4 s was demonstrated. Five prepared gas mixtures and 15 exhaled breath samples were measured with both the NO sensor and for intercomparison with a chemiluminescence-based NO analyzer and were found to be in agreement within 0.6 ppbv. Exhaled NO flow-independent parameters, which may provide diagnostic and therapeutic information in respiratory diseases where single-breath measurements are equivocal, were estimated from end-tidal NO concentration measurements collected at various flow rates. The results of this work indicate that a laser-based exhaled NO sensor can be used to measure exhaled nitric oxide at a range of exhalation flow rates to determine flow-independent parameters in human clinical trials. PACS 07.07.Df; 33.20.Ea; 42.62.Fi; 87.80.-y