Nitric oxide concentrations measured from the inspiratory limb of the ventilatory circuit and the endotracheal tube in a lung model and a patient on the artificial ventilation, during sequential administration. Panel A represents the variations in NO concentration in the inspiratory limb in the lung model; panel B shows the variations in NO concentration at simulated tracheal level in the lung model; panel C shows the variations in NO concentration in the inspiratory limb in the ventilated patient; panel D shows the variations in NO concentration in the trachea of the ventilated patient. In panels A and B the lower trace represents the respiratory gas flow. In panels C and D the two lower traces represent expired CO2 curves (end-tidal CO2 = 25 mmHg) and respiratory gas flow. Nitric oxide concentrations were measured by fast-response chemiluminescence apparatus (NOX 4000 Sérès, Aix-en-Provence, France). The time delay of the apparatus was 2.4 s. Accordingly, the beginning of inspiration and expiration (represented by arrows) is shifted 2.4 s to the right compared to the respiratory flow recording. Published with permission .