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

Patterson, Robert N; Johnston, Brian T; Ardill, Joy E S; Heaney, Liam G; McGarvey, Lorcan P A

doi:10.1136/thx.2006.063982

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

¹Department of Medicine, Queen’s University Belfast, Belfast, UK
²Regional Respiratory Centre, Belfast City Hospital, Belfast, UK
³GI Physiology Unit, Royal Victoria Hospital, Belfast, UK

Correspondence to:
Dr Lorcan McGarvey
Department of Medicine, Grosvenor Road, Belfast BT12 6BJ, UK; l.mcgarvey{at}qub.ac.uk

Received 3 May 2006
Accepted 25 November 2006
Published Online First 24 January 2007

Abstract

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 α₂-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.