Monitoring of fast variations in the content of endogenous CO in exhaled air by methods of diode laser spectroscopy

Methods of diode laser spectroscopy were applied for monitoring of fast physiological variations in the content of endogenous carbon monoxide (CO) in exhaled air. To this end, a CO analyzer based on a tunable diode laser emitting radiation around 2.35 $\mu$m at room temperature was constructed. CO concentration in exhaled air was determined by measuring resonance absorption of CO molecule at the $R$ (6) line of the 0–2 band in the vicinity of 4285 cm$^{-1}$. Using this line that is well separated from the nearby absorption lines of Н$_2$О enables high selectivity of CO analysis under the conditions of high humidity of analyzed air. The possibility of monitoring fast physiological variations of CO content in exhaled air of humans and animals by means of the developed system was demonstrated in studies involving a number of physiological load tests, such as breathing pure oxygen (both humans and rats), physical load, and hyperventilation. The dynamics of CO release caused by certain pharmaceutical drugs was also studied. It is demonstrated that laser diagnostics of CO in the spectral region near 2.35 $\mu$m allows detecting fast dynamic processes of release of this gas molecule that represents one of the signaling and metabolite molecules in exhaled air when conducting various physiological and medical studies, investigating trends and interrelation of processes responsible for production, transport, buffering, and release of CO in an organism.