Variations in NO concentration in the inspiratory limb with a healthy volunteer on pressure support ventilation receiving NO by sequential method. The subject breathed from the ventilator through an air-tight mask. Nitric oxide was administered in sequential mode by the Opti-NO (Taema, Anthony, France). The Opti-NO settings corresponding to 3 ppm in the bellows of the lung model and a pressure support of 10 cmH2O were utilized. Inspiratory NO concentrations were measured by fast-response chemiluminescence apparatus having a time delay of 2.4 s. The scale at the top of the recording indicates time (interval between two consecutive bars represents 1 s). From top to bottom, the traces correspond to airway pressure, inspired NO concentration, expired tidal volume and respiratory flow. With the level of pressure support and the settings of the Opti-NO remaining constant, inspired NO concentration varied by more than 200% as a function of varying tidal volume and inspiratory time. A decrease in the tidal volume or an increase in the inspiratory time was associated with an increase in the inspired NO concentration. Published with permission .