Respiratory Muscle Strength and Mortality in Patients with COPD: A Systematic Review and Meta-Analysis

Abstract

Purpose: Respiratory muscle weakness is common in chronic obstructive pulmonary disease (COPD), potentially carrying prognostic information beyond airflow limitation; however, clinical testing remains variably standardized, and its independent association with survival is uncertain. We evaluated whether respiratory muscle strength is associated with survival in patients with COPD, and summarized implementation-relevant evidence for other indices. Methods: We systematically searched PubMed/MEDLINE, CENTRAL, and Web of Science from January 1, 1990 to September 30, 2025, screened observational cohorts and baseline-prognosis analyses in patients with COPD, appraised risk of bias, and meta-analyzed time-to-event estimates using random-effects where ≥2 comparable studies were available. Eligible studies enrolled patients with COPD with observational cohorts or baseline-prognosis analyses reporting all-cause mortality as outcome. Results: Of the six eligible studies, two permitted pooling for inspiratory strength versus all-cause mortality. Lower inspiratory strength was associated with higher mortality (pooled hazard ratio 0.97, 95% confidence interval 0.95–0.99; I2=58%). In severity-restricted cohorts, frequently reported cut-offs were maximal inspiratory strength (MIP) ≤55 cmH2O and maximal expiratory strength (MEP) ≤80 cmH2O; all-cause mortality in these groups was approximately 46.6–54.4% at 42–60 months. However, in broader-severity samples, 2-year and 12–45-month mortality rates were 9.4–14.7% and 8.4–33.6%, respectively. Peak inspiratory flow rate (PIFR) <60 L/min repeatedly aligned with exacerbations and 90-day readmission. Conversely, the prognostic signal for MEP was directionally inconsistent, and sniff nasal inspiratory pressure associations frequently attenuated after adjustment. Conclusion: MIP shows a consistent directional association with survival in patients with COPD, although magnitude estimates vary with measurement protocols and confounder control. We propose a minimum reporting set (posture, starting lung volume, trials/repeatability, device/calibration, cmH2O units, and prespecified confounders) and immediate clinical actions: standardized MIP during stable visits for risk stratification and PIFR screening to guide inhaler selection.