A Cochrane review included 8 cross-over studies with a total of 96 subjects. The active interventions studied varied greatly between the included studies: one included study looked at autogenic drainage, 6 considered conventional chest physiotherapy, 3 considered oscillating positive expiratory pressure, 7 considered positive expiratory pressure and 1 considered high pressure positive expiratory pressure. Of the 8 studies, 6 were single-treatment studies and in 2, the treatment intervention was performed over 2 consecutive days (once daily in one, twice daily in the other). No meta-analyses was possible.
Four studies (n=28) reported a higher amount of expectorated secretions during chest physiotherapy as compared to a control. One study (n=18) reported no significant differences in sputum weight. In 5 studies radioactive tracer clearance was used as an outcome variable; in 3 of these (n=28) it was reported that chest physiotherapy, including coughing, increased radioactive tracer clearance as compared to the control period. One study (n=12) reported increased radioactive tracer clearance associated with all interventions compared to control, although this was only reported to have reached significance for postural drainage with percussion and vibrations; and the remaining study (n=8) reported no significant difference in radioactive tracer clearance between chest physiotherapy, without coughing, compared to the control period. Three studies (n=42) reported no significant effect on pulmonary function variables following intervention; but 1 further study did report significant improvement in pulmonary function following the intervention in some of the treatment groups.
Comment: The quality of evidence is downgraded by study quality (unclear allocation concealment and blinding) and by inconsistency (variability in results).