Table 2 Clinical and physiological characteristics of obstructive airway syndromes
AsthmaOverlap syndromeCOPDHealthy
Symptoms+++−
FEV1/FVC⩾70%<70%<70%⩾70%
FEV1 % predicted*>80%<80%<80%>80%
AHR, PD15†<12 ml<12 ml>12 ml>12 ml

  • *Postbronchodilator

  • †PD15, provocation dose of hypertonic saline that induces a 15% fall in FEV1.

  • AHR, airway hyper-responsiveness; COPD, chronic obstructive pulmonary disease; FEV1, forced expiratory volume in 1 s; FVC, forced vital capacity.