Airway reactions and breathing movements in sensory hyperreactivity

Patients diagnosed with sensory hyperreactivity (SHR), suffer from airway symptoms such as cough, breathing difficulties and chest pain, induced by a variety of environmental irritants, as well as by cold air and physical effort. Their lung function tests show normal values and specific asthma tests are usually negative. Capsaicin, the hot ingredient in hot peppers (capsicum), is known to stimulate the cough reflex in humans and is used to distinguish and diagnose this condition. SHR affects more than 6% of the adult Swedish population, mainly women and there is no pharmacotherapy to offer. The overall aim of this thesis was to elucidate different aspects of symptoms and reactions, from the airways and the chest for which these patients seek medical attention for. A further aim was to evaluate the effect of a physiotherapeutic intervention. Study I evaluated the induced symptoms; physiological parameters and capsaicin cough sensitivity in patients suffering from exercise induced dyspnea (EID) and SHR, after exercise in cold air. Study II evaluated capsaicin cough sensitivity in patients with SHR and chronic idiopathic cough after a eucapnic voluntary hyperventilation (EVH) test. Study III evaluated chest mobility, respiratory movement and pain sensitivity in patients with SHR compared with patients with asthma, chronic obstructive pulmonary disease (COPD) and allegedly healthy control subjects. Study IV evaluated the effect of a 12-week physiotherapeutic home based training program in patients diagnosed with SHR. Main findings: Exercise provocation in cold air increased capsaicin cough sensitivity and decreased end-tidal CO2 without affecting lung function. When provoked with the EVH test, cough sensitivity was down-regulated. The patients with SHR had increased breathing frequency, reduced chest mobility and lower respiratory movement compared to both healthy control subjects and to patients with asthma. Except for lung function, the significantly younger group of patients with SHR was comparable, in several aspects with the group of older patients suffering from severe or very severe COPD. Further, patients with asthma, COPD and SHR had significantly lower pain thresholds compared to the healthy controls. A physiotherapeutic home based training program increased chest mobility and decreased the subjective feeling of chest pressure after the training period. The capsaicin cough threshold for two coughs (C2) increased (improved) after the intervention period. Conclusions: Patients suffering from SHR have in many ways reactions differing from healthy control subjects and from patients with other airway diseases. However, in some aspects, like breathing symptoms, pain sensitivity and chest mobility, the findings in the various airway diseases overlapped each other. The airway symptoms and the increased cough sensitivity reported by the patients with SHR are reproducible by exercise in cold air. On the other hand an EVH test, in line with animal studies and results in healthy volunteers, had the opposite effect and down-regulated the cough sensitivity following the EVH test. That a physiotherapeutic treatment program turned out to be effective in enhancing chest mobility, decreasing chest symptoms and improving capsaicin cough sensitivity indicates a possibility to provide a treatment for these patients. We hypothesize that cold air, exercise and dry air via the recently identified receptor system of transient receptor potential (TRP) ion channels influenced cough and other airway symptoms among the patients. The findings may provide an explanation for some of the airway and chest symptoms reported by patients suffering from SHR.