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

A nitric oxide (NO) sensor employing a ther- moelectrically cooled, continuous-wave, distributed feedback quantum cascade laser operating at 5.47 µm (1828 cm −1 )a nd off-axis integrated cavity output spectroscopy was used to meas- ure NO concentrations in exhaled breath. A minimum mea- surable concentration (3σ) of 3.6 parts-per-billion by volume (ppbv) of NO with a data-acquisition time of 4 s was demon- strated. Five prepared gas mixtures and 15 exhaled breath samples were measured with both the NO sensor and for in- tercomparison 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 diagnos- tic 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 ex- haled 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.