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Enhanced sensory nerve reactivity in non-eosinophilic asthma
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  • Hajar Ali,
  • Collin Brooks,
  • Julian Crane,
  • Richard Beasley,
  • Stephen Holgate,
  • Peter Gerard Gibson,
  • Philip Pattemore,
  • Yu-Chieh Tzeng,
  • Thorsten Stanley,
  • Neil Pearce,
  • Jeroen Douwes
Hajar Ali
Massey University
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Collin Brooks
Massey University Centre for Public Health Research
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Julian Crane
Wellington School of Medicine & Health Sciences
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Richard Beasley
Medical Research Institute of NZ
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Stephen Holgate
University of Southampton
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Peter Gerard Gibson
The University of Newcastle Hunter Medical Research Institute
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Philip Pattemore
Christchurch School of Medicine
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Yu-Chieh Tzeng
University of Otago, Wellington, NZ
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Thorsten Stanley
University of Otago
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Neil Pearce
London School of Hygiene and Tropical Medicine
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Jeroen Douwes
Massey University
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Abstract

ABSTRACT Background: Neural mechanisms may play an important role in non-eosinophilic asthma. This study compared airway sensory nerve reactivity, using capsaicin challenge, in eosinophilic and non-eosinophilic asthma and non-asthmatics. Methods: Thirty-eight asthmatics and nineteen non-asthmatics (aged 14-21 years) underwent combined hypertonic saline challenge/sputum induction, exhaled nitric oxide (FeNO), atopy, and spirometry tests, followed by capsaicin challenge. Eosinophilic (EA) and non-eosinophilic asthma (NEA) were defined using a sputum eosinophil cut-point of 2.5%. Airway hyperreactivity (AHR) was defined as a ≥15% drop in FEV1 during saline challenge. Sensory nerve reactivity was defined as the lowest capsaicin concentration that evoked 5 (C5) coughs. Results: Non-eosinophilic asthmatics (n=20) had heightened capsaicin sensitivity (lower C5) compared to non-asthmatics (n=19) (geometric mean C5: 58.3μM, 95% confidence interval 24.1-141.5 vs 193.6μM, 82.2-456.0; p<0.05). There was a similar (but non-significant) difference in capsaicin sensitivity in NEA compared with EA (n=18), (58.3μM, 24.1-141.5 vs 191.0μM, 70.9-514.0; p=0.07). FEV1 was significantly reduced from baseline following capsaicin inhalation in both asthmatics and non-asthmatics but no differences were found between subgroups. No associations with capsaicin sensitivity and atopy, sputum eosinophils, blood eosinophils, asthma control, or treatment were observed. Conclusion: Non-eosinophilic asthma, but not eosinophilic asthma, showed enhanced capsaicin sensitivity compared with non-asthmatics. Sensory nerve reactivity may therefore play an important role in the pathophysiology of non-eosinophilic asthma.