Heightened cough response to bronchoconstriction in cough variant asthma

Background and objective:  The pathophysiology of cough variant asthma (CVA) is poorly understood. We compared bronchoconstriction-triggered cough between CVA patients and normal control (NC) subjects. Methods:  There were two protocols in the study. We measured bronchial responsiveness to methacholine (MCh) and counted the number of coughs in nine CVA patients and seven NC subjects (Study A). Using partial and full flow–volume curves, expiratory flow of the partial flow–volume curve at 40% above residual volume level (PEF40) and FEV1 were used to measure bronchoconstriction. Mild bronchoconstriction was defined as a 35% fall in PEF40 (PC35-PEF40), and more severe bronchoconstriction as a 20% fall in FEV1 (PC20-FEV1). In study B, the same measurements were obtained in six CVA patients before and after therapy. Results:  In study A, more coughs were provoked at PC35-PEF40 in CVA patients (median, 60 coughs/32 min post challenge; range, 12–135) than in NC subjects (median, 0/32 min; range, 0–13; P < 0.05). At PC20-FEV1, more coughs were provoked in CVA patients (median, 60/32 min; range, 12–150) than in NC subjects (median, 20/32 min; range, 0–54; P < 0.05). In study B, the six CVA patients who underwent re-examination after treatment had less coughs at PC35-PEF40 (median, 3/32 min; range, 0–14) and PC20-FEV1 (median, 13/32 min; range, 3–26) after therapy than before therapy (median, 54/32 min; range, 33–125 and 52/32 min, 45–96, respectively; P < 0.05). Conclusions:  We identified heightened cough response to bronchoconstriction as a feature of CVA.