Positive expiratory pressure in patients with chronic obstructive pulmonary disease--a systematic review. 
Breathing exercises against a resistance during expiration are often used as treatment for patients with chronic obstructive pulmonary disease (COPD).  Controversy still exists regarding the clinical application and efficacy.  The aim of this systematic review was to determine the effects of chest physiotherapy techniques with positive expiratory pressure (PEP) for the prevention and treatment of pulmonary impairment in adults with COPD.  The review was conducted on randomised, controlled clinical trials in which breathing exercises with positive expiratory pressure were compared with other chest physical therapy techniques or with no treatment, in adult patients with COPD.  A computer-assisted literature search of available databases from 1970 to January 2008 was performed.  Two reviewers extracted data independently and assessed the trials systematically with an instrument for measuring methodological quality.  In total, 11 trials met the inclusion criteria, of which 5 reached an adequate level of internal validity.  Several kinds of PEP techniques with a diversity of intensities and durations of treatment have been evaluated with different outcome measures and follow-up periods.  Benefits of PEP were found in isolated outcome measures in separate studies with a follow-up period <1 month.  Concerning long-term effects, the results are contradictory.  Prior to widespread prescription of long-term PEP treatment, more research is required to establish the benefit of the technique in patients with COPD.