Mucociliary clearance is an essential defense mechanism of the lungs that helps remove inhaled particles, pathogens, and airway secretions. This process depends on the coordinated action of cilia, mucus properties, and airway hydration. In healthy individuals, mucus is continuously transported toward the throat, allowing effective clearance of harmful substances. However, this mechanism can be influenced by the hydration status of the airway surface liquid.

Heated humidification delivered through high-flow nasal cannula (HFNC) has been shown to improve airway hydration, enhance ciliary function, and support mucociliary clearance. In addition, nebulized saline solutions are commonly used to modify mucus properties. Hypertonic saline has demonstrated short-term benefits in improving mucus hydration and clearance, but its use may be associated with side effects such as airway irritation or bronchoconstriction. In contrast, the effects of isotonic saline remain unclear, particularly when delivered in large volumes.

The rationale of this study is that continuous nebulization of isotonic saline, when combined with heated humidification, may provide a sufficient cumulative amount of sodium to improve airway hydration and mucociliary clearance, potentially mimicking the effects of hypertonic saline without its adverse effects.

This study is a randomized controlled cross-over trial conducted in healthy adult volunteers. Each participant will undergo three experimental sessions: a baseline assessment without intervention, a control condition with heated humidification alone, and an intervention condition combining heated humidification with continuous isotonic saline nebulization. The order of the control and intervention sessions will be randomized.

Mucociliary clearance will be assessed using pulmonary scintigraphy. Participants will inhale radiolabeled aerosol particles (99mTc-DTPA), and the clearance of these particles from the lungs will be monitored over time using a gamma camera. Images will be acquired at regular intervals to quantify the rate of particle retention and clearance under each condition.

The primary objective of the study is to determine whether continuous isotonic saline nebulization combined with heated humidification improves mucociliary clearance compared to heated humidification alone.

Secondary outcomes include the evolution of mucociliary clearance over time during and after the intervention, as well as participant comfort assessed using a Likert scale.

The findings of this study may help improve understanding of airway hydration strategies and contribute to optimizing respiratory care techniques aimed at enhancing mucus clearance.