Small and large airway reactions to osmotic stimuli in asthma and chronic idiopathic cough

Chronic cough is a common symptom and related to several pulmonary, airway and heart diseases. When all likely medical explanations for the coughing are excluded, there remains a large group of patients with chronic coughing, which is mostly a cough reflex easily triggered by environmental irritants and noxious stimuli. The main aim of this study was to improve the diagnostic ability to differentiate chronic idiopathic cough (CIC) from asthma.

Twenty-three patients with CIC, 16 patients with mild asthma and 21 control participants were included. The study consisted of three randomised bronchial provocations with osmotic stimuli: mannitol, eucapnic dry air and hypertonic saline. At each provocation lung function was assessed by spirometry and impulse oscillometry (IOS).

In a comparison of the groups, while the FEV₁ measurements did not differ, the CIC group had increased airway resistance and reactance after provocation with hypertonic saline compared to the control subjects. After mannitol provocation the patients with asthma had significantly increased airway resistance compared to the controls and from eucapnic dry air provocations these patients had a significant reduction in spirometry values and increased airway resistance compared to both the patients with CIC and the controls.

The asthma group reacted in a predictable way with impaired lung function from osmotic provocations, whereas the patients with CIC demonstrated peripheral airway changes from hypertonic saline, also known to be a noxious stimulus. The IOS method uncovers differences between patients with CIC and control participants that contribute to our ability to provide a correct diagnosis.