Adverse effect of previous bronchial asthma on disability in chronic airflow obstruction.

The average distance covered when attempting to hurry on the level for 12 min (12 min walking distance) is linearly correlated to forced expiratory volume in 1 s in healthy middle-aged individuals and patients with chronic airflow obstruction. Patients with current or past asthma, with or without chronic bronchitis and emphysema, walk more slowly than those with chronic obstructive pulmonary disease for a similar degree of airflow obstruction. A previous history of asthma may be a factor in the limitation of effort caused by chronic respiratory disease.