The citric acid cough reflex test, or inhalation cough challenge, offers potential for improving clinical detection of silent aspiration in dysphagia assessment. For any new technique to be accepted as a clinically relevant tool, established validity, reliability, and normative data are requisite. This study presents a normative data set for the citric acid cough reflex test using a facemask method. Data were collected from 160 healthy participants, equally represented by gender and in two age groups (under 60 years of age and over 60 years of age). They passively inhaled, via facemask, three trials of nebulized citric acid of 10 different concentrations: study A ranging from 0.8 to 2.6 mol/l and study B ranging from 0.1 to 1.2 mol/l, with placebo interspersed. Natural cough thresholds (NCT) and suppressed cough thresholds (SCTs) were reached when subjects produced two successive coughs on at least two out of three trials. While 5% of participants failed to trigger a cough at any concentration, of those that did, the majority of participants (89.5%) reached NCT by 0.8 mol/l, with 95.5% demonstrating SCT by 1.2 mo/l. In study B, using lower concentrations of citric acid, there were significant differences between genders for both NCT (P = 0.001) and SCT (P = 0.004) that were not apparent in study A given the flooring effect. While no difference was found between age groups for NCT (P = 0.361), in Study A, which tested higher concentrations of citric acid, a significant difference between age groups in cough suppression was revealed (P = 0.009) with youngers being able to suppress cough at higher levels.

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