Increased tachykinin levels in induced sputum from asthmatic and cough patients with acid reflux

Background: Acid reflux may aggravate airway disease including asthma and chronic cough. One postulated mechanism concerns a vagally-mediated oesophageal- tracheobronchial reflex with airway sensory nerve activation and tachykinin release. Aim: To test the hypothesis that patients with airways disease and reflux have higher airway tachykinin levels than those without reflux. Methods: Thirty- two patients with airways disease ( 16 with mild asthma and 16 non- asthmatic subjects with chronic cough) underwent 24 h oesophageal pH monitoring. Acid reflux was defined as increased total oesophageal acid exposure (% total time pH < 4 of > 4.9% at the distal probe). All subjects underwent sputum induction. Differential cell counts and concentrations of substance P ( SP), neurokinin A ( NKA), albumin and alpha(2)- macroglobulin were determined. Results: SP and NKA levels were significantly higher in patients with reflux than in those without ( SP: 1434 ( 680) pg/ ml vs 906 ( 593) pg/ ml, p = 0.026; NKA: 81 ( 33) pg/ ml vs 52 ( 36) pg/ ml, p = 0.03). Significantly higher tachykinin levels were also found in asthmatic patients with reflux than in asthmatic patients without reflux ( SP: 1508 ( 781) pg/ ml vs 737 ( 512) pg/ ml, p = 0.035; NKA: median ( interquartile range 108 ( 85 120) pg/ ml vs 75 ( 2 - 98) pg/ ml, p = 0.02). In patients with asthma there was a significant positive correlation between distal oesophageal acid exposure and SP levels ( r = 0.59, p = 0.01) and NKA levels ( r = 0.56, p = 0.02). Non- significant increases in SP and NKA were measured in patients with cough with reflux ( SP: 1534.71 ( 711) pg/ ml vs 1089 ( 606) pg/ ml, p = 0.20; NKA: 56 ( 43) pg/ ml vs 49 ( 17) pg/ ml, p = 0.71). No significant difference in differential cell counts or any other biochemical parameter was noted between study groups. Conclusion: This study demonstrates increased airway tachykinin levels in patients with asthma and cough patients with coexistent acid reflux. This suggests airway sensory nerve activation in this population.