Respiratory movement and pain thresholds in airway environmental sensitivity, asthma and COPD

Patients with "sensory hyperreactivity" (SHR) have airway environmental sensitivity, chronic cough and dyspnoea. Cough, chest discomfort and sense of difficulties getting air are some of the symptoms these patients seek medical attendance for. The patients have increased cough sensitivity to inhaled capsaicin, mediated by ion channel receptors on sensory nerves also known to react to pain stimuli. Whether a link exists between capsaicin airway sensitivity and pain sensitivity has not yet been evaluated. The aim was to investigate chest mobility, respiratory movement and pain sensitivity in SHR patients compared with patients with asthma, chronic obstructive pulmonary disease (COPD) and alleged healthy control subjects.

Thirty-five patients diagnosed with SHR, 19 with COPD, 32 with asthma and 28 control subjects were included. Chest expansion was measured with a measuring tape and thoracic and abdominal movement with light sensors. Pain sensitivity was assessed using a pressure algometer.

Groups differed significantly in lung function, respiratory rate and pain sensitivity but also in chest expansion and abdominal breathing movement. In comparison with the control and asthma groups but not the COPD patients, SHR patients had an increased respiratory rate and reduced abdominal movement during deep breathing. All patient groups showed lower pain thresholds than the controls.

Patients with SHR have evident signs of dysfunctional breathing and appeared to be most similar to the COPD group except for lung function. Lower pain thresholds among the patients indicate a general up-regulation of the sensory nerve system.