Effectiveness of expiratory muscle strength training on expiratory strength, pulmonary function and cough in the adult population: a systematic review.

Background: Respiratory muscle strength declines in certain disease states, leading to impaired cough, reduced airway clearance and an increased risk of aspiration pneumonia. Respiratory muscle training may therefore reduce this risk.

Objectives: To assess current evidence of expiratory muscle strength training (EMST) on maximum expiratory pressure, cough flow and spirometry.

Data Sources: Databases including CINAHL, Medline, Science Direct and PEDRo were searched.

Eligibility Criteria: Randomised controlled trials investigating expiratory muscle strength training on maximum expiratory pressure, pulmonary function or cough in any adult population, published before December 2017.

Study Appraisal: Data were extracted to a trial description form and study quality evaluated by two reviewers. Meta-analysis was performed with calculation of mean differences and 95% confidence intervals.

Results: Nine studies met inclusion criteria and ranged in size from 12 to 42 participants. Trials investigated EMST in healthy adults (2), multiple sclerosis (3), COPD (2), acute stroke (1) and spinal cord injury (1). Overall, EMST improved maximum expiratory pressure (15.95cmHO; 95% CI: 7.77 to 24.12; P<0.01) with no significant impact on cough flow (4.63L/minute; 95%CI -27.48 to 36.74; P=0.78), forced vital capacity (-0.16L; 95%CI -0.35 to 0.02; P=0.09) or forced expiratory volume in 1second (-0.09L; 95%CI -0.10 to -0.08; P<0.001) vs control or sham training.

Conclusions: Meta-analysis indicated a small significant increase in maximum expiratory pressure following EMST. Improvements in maximum expiratory pressure did not lead to improvements in cough or pulmonary function.

Limitations: Variations in protocol design and population limited the overall effect size. Systematic Review Registration PROSPERO CRD42018104190.