Exploratory and safety study: Modulation of the cough reflex using ultrasonically nebulised distilled water (UNDW) in healthy participants.

In this study, we wanted to know whether we could safely modulate and enhance cough sensitivity using inhalations of distilled water. The distilled water senosory stimulation protocol was designed as a potential treatment for silent aspiration, where individuals aspirate due to a lack of sensation in their throat. We wanted to determine if the sensory stimulation protocol was safe on pulmonary function and whether it could modulate cough sensitivity. We recruited 28 healthy volunteers to undergo the distilled water sensory stimulation protocol. Four participants were excluded, as they were not suitable to participate in the study. A total of 24 individuals, 8 per group, were included in the final analysis. The distilled water sensory stimulation protocol did not induce narrowing of the airways (i.e. bronchoconstriction) in any participant. Cough sensitivity changed differently across days in the high and low-intensity sensory stimulation groups, compared to the control group. In the control group, cough sensitivity increased across days. This is what we expect when we repeat the citric acid cough reflex test across days. In contrast, an absence of habituation to citric acid CRT was observed following both of the sensory stimulation protocols, suggesting an increase in cough sensitivity.