Quantum cascade laser-based sensors for the detection of exhaled carbon monoxide

Real-time breath gas analysis of CO and CO2 using an EC-QCL

“…However, the findings are partly in contrast to investigations by Zetterquist et al [31] and Pakmanesh et al [33], where only a dependence on breath-holding time was observed. Possible reasons for this discrepancy include differences in the breath sampling procedure and lack of sufficient sensitivity and real-time capability to precisely measure eCO expirograms and resolve the flow rate dependence.…”

“…The sensitivity was ultimately limited by fluctuations in the wavelength-dependent background caused by fringes. Due to the use of an MPC and WMS curve fitting, the sensitivity and precision of real-time eCO detection are at least a factor of ten better than those for typical single-pass WMS setups [33]. This results in more accurate and precise eCO expirograms and provides the possibility to quantify indoor air CO.…”

“…The longer the breath is held in the respiratory system, the more time there is for the alveolar, CO-enriched air to equilibrate with dead space air by axial diffusion. In addition, blood CO may constantly diffuse into the alveoli [33], which would explain the increasing phase III plateau and end-tidal concentrations that probably approach the alveolar CO concentration. A low exhalation Single eCO exhalation profiles from subject 2 (same data as in Fig.…”

“…Gas exchange with the airway wall lining fluids is unlikely due to the low water-solubility of CO. One rationale is that blood CO is not in equilibrium with the lungs and CO is constantly diffusing into alveolar air [33], from where it is distributed to the respiratory tract by axial diffusion. However, there could also be CO release from tissue in lung or airways.…”

“…Due to its low proton affinity, CO is rarely measured with standard soft-ionization MS, and eCO detection with solid state, chemiluminescence and near-infrared sensors lacks the required time-resolution for real-time BGA [31]. Recent efforts with laser spectroscopy [25,[32][33][34] revealed controversial results regarding the dependence of eCO on exhalation flow rate and breath-holding time.…”