Airway sensitivity to chemicals and scents. Sympoms, trigger factors and the capsaicin inhalation test

Some patients with airway symptoms, induced by chemicals and scents, but who lackbronchoconstriction or allergy, have shown increased cough sensitivity to inhaled capsaicin. Capsaicinstimulates cough via the sensory nervous system, and a suggested diagnosis for this condition issensory hyperreactivity (SHR).The aims of this thesis were to; (I) study airway sensitivity to inhaled capsaicin, and the occurrenceof airway symptoms induced by chemicals and scents in patients with airway symptoms of unclearaetiology; (II) clarify whether patients with multiple chemical sensitivity (MCS) according to Cullen scriteria have a physiologically substantiated reaction (cough) to inhaled capsaicin that differed fromhealthy controls; (III) compare tidal breathing and dosimeter methods in terms of agreement andrepeatability of cough response to capsaicin inhalation in patients with SHR and in healthy controls;(IV) evaluate the long-term persistence of airway symptoms induced by chemicals and scents and theirinfluence on health-related quality of life (HRQL), and determine the long-term reproducibility ofcough response to capsaicin inhalation.Cough sensitivity to capsaicin was dose dependent and was significantly higher among the patientsthan in the healthy controls (I IV).Fifty-two patients underwent methacholine and capsaicin inhalation tests. Twenty-three percent(12/52) of the patients had a positive methacholine test, of these nine were diagnosed as havingasthma. Seventy-seven percent (40/52) of the patients reported airway symptoms induced bychemicals and scents and they coughed significantly more to inhaled capsaicin than did those withoutsuch sensitivity (I).Twelve patients with MCS, all having airway symptoms induced by chemicals and scents, wereprovoked with inhalation of capsaicin, in a double-blind randomised order, and the resulting responseswere compared with 12 healthy controls. The patients coughed significantly more and experiencedmore other airway symptoms upon capsaicin inhalation than the controls did (II).In 15 patients with SHR and 15 healthy controls, capsaicin inhalation tests were performed twiceusing tidal breathing and twice using the dosimeter method. The dosimeter method causedsignificantly more coughs and other airway symptoms in both patients and controls than did the tidalbreathing method. Both methods showed good repeatability and a similar ability to distinguish patientswith SHR from controls (III).Eighteen patients with airway symptoms induced by chemicals and scents were followed for fiveyears. In most patients the symptoms and a reduced HRQL persisted, and the capsaicin coughsensitivity was increased, reproducible, and long lasting (IV).Conclusion: In patients with SHR and MCS airway sensory reactivity is increased, suggesting thatneurogenic factors may be of importance. Though the methacholine inhalation test may be of somevalue in assessing these patients, in that it can exclude the possibility of bronchial asthma, thecapsaicin inhalation test seems to be a more useful diagnostic tool. In conducting capsaicin inhalationtesting it is important to know the type of inhalation device used, particle size, airflow rate, andinspiratory flow rate, as these factors influence the strength of reaction. SHR appears to be a chroniccondition; it is associated with reduced HRQL and the long-term persistence of increased capsaicincough sensitivity.Key words: asthma, capsaicin, cough, dosimeter method, health-related quality of life,methacholine, multiple chemical sensitivity, Nottingham Health Profile, sensory hyperreactivity, tidalbreathing metho