We find it interesting that PEP alone showed a uniform pattern of significant increases in PEF, though to a minor extent than after terbutaline treatment, indicating that PEP alone dilates airways. This is in accordance with findings from studies concerning pursed-lip breathing in COPD,2 as well as CPAP in induced asthma, expiration in a 10-cm HaO column in exercise-induced asthma, and PEP-mask giving reduced volume of trapped gas in cystic fibrosis. The increased pressure in the airways created by the different forms of expiratory positive pressure seems to distend bronchi and bronchioles.
In patients with expiratory airflow limitation, collapse of airways during expiration occurs to a greater extent than in healthy subjects, and during PEP the pressure gradients are moved from the airways to the PEP-resistance, leaving the airways more open. In this way the distribution of the ventilation and thereby the deposition of inhaled medication might be improved, giving further bron-chodilation. The retarded expiration might allow more time for retaining the medication in the distal airways. The various forms of PEP, including pursed-lip breathing, may have similar effects provided that inhalation of medication is simultaneous with the application of expiratory pressure.
Opening of the airways might enhance mobilization of airway secretion, which could contribute to the increase in PEF after PEP alone.