Abstract
Carbon monoxide (CO) monitoring in human breath is the focus of many investigations as CO could possibly be used as a marker of various diseases. Detecting CO in human breath remains a challenge because low concentrations (<ppm) must be selectively detected and short response time resolution is needed to detect the end expiratory values reflecting actual alveolar concentrations. A laser spectroscopy based instrument was developed (ProCeas) that fulfils these requirements. The aim of this study was to validate the use of a ProCeas for human breath analysis in order to measure the changes of endogenous exhaled CO (eCO) induced by different inspired fractions of oxygen (FiO2) ranging between 21% and 100%. This study was performed on healthy volunteers. 30 healthy awaked volunteers (including asymptomatic smokers) breathed spontaneously through a facial mask connected to the respiratory circuit of an anesthesiology station. FiO2 was fixed to 21%, 50% and 100% for periods of 5 minutes. CO concentrations were continuously monitored throughout the experiment with a ProCeas connected to the airway circuit. The respiratory cycles being resolved, eCO concentration is defined by the difference between the value at the end of the exhalation phase and the level during inhalation phase. Inhalation of 100% FiO2 increased eCO levels by a factor of four in every subjects (smokers and non smokers). eCO returned in a few minutes to the initial value when FiO2 was switched back to 21%. This magnification of eCO at 21% and 100% FiO2 is greater than those described in previous publications. We hypothesize that these results can be explained by the healthy status of our subjects (with low basal levels of eCO) and also by the better measurement precision of ProCeas.
Highlights
Monitoring the endogenous carbon monoxide in exhaled breath is of growing interest in clinical studies
Carbon monoxyde (CO) concentration gas in the airway circuit was monitored in real time during all the 30 minutes breathing by the ProCeas analyzer
Measurements during inhalation phases allow to deduce the CO background in inhaled air that is cycle by cycle subtracted to the exhaled CO concentration values, as described above in the methods section
Summary
Monitoring the endogenous carbon monoxide in exhaled breath (eCO) is of growing interest in clinical studies. This rapid and non-invasive measurement may reveal various pathological conditions. Carbon monoxyde (CO) has been extensively studied, as it is well known as a toxic gas in ambient air due to incomplete combustion of organic products Beyond this external toxic effect, CO is normally produced endogenously by the degradation of heme porphyrins to biliverdin and iron (bilirubin metabolism or heme catbolism). Some clinical studies require eCO continuous monitoring with a sensitive and reliable device allowing cycle to cycle variation measurements by high frequency sampling This allows to accurately monitor the eCO deduced from the value measured at the end of the exhalation phase to which is subtracted the CO background measured during the inhalation phase. Increasing FiO2 was already used for studying variations of eCO in spontaneously breathing patients just before cardiac surgery[14] and in mechanically ventilated patients under general anesthesia[15,16]
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