Bronchodilatory effect of warm air inhalation during quiet breathing

To evaluate the effects of air warming and humidification, we examined the spirometric responses before and after exposure to a conditioned airstream. Seven healthy subjects, seven clinically stable patients with chronic bronchitis and seven clinically stable asthmatic patients were studied during quiet breathing. All were exposed to the following air conditions for 10 minutes: -20°C, dry; 37°C, dry; 37°C, fully saturated; 50°C, dry, and 50°C, fully saturated. As heat increased, airflow progressively improved in asthmatic persons as a group. In contrast, patients with chronic bronchitis, who had more severe underlying airflow obstruction, had most improved airflow with warm dry air inhalation and showed less improvement as humidity was added isothermally. We conclude that active warming of air before inhalation can improve airflow significantly in some patients with reactive obstructed airways, and that high degrees of humidity may exert an independent adverse effect in persons with chronic bronchitis or in those with serious airflow obstruction.