Impact of Inspiratory Muscle Strength and Lung Function on Functional Exercise Capacity in Post-myocardial Infarction Patients: A Cross-sectional Study.

Objective: This study aims to investigate the contribution of lung function and respiratory muscle strength in predicting functional exercise capacity in post-myocardial infarction (MI) subjects.

Material and methods: This cross-sectional study included 56 stable post-MI subjects. Lung function was assessed using a digital spirometer, and respiratory muscle strength was measured using an intraoral pressure meter. The 6-minute walk distance (6MWD) was conducted to assess functional exercise capacity. Correlations and multiple regression analyses were performed to evaluate predictors of 6MWD, considering demographic factors, lung function, and respiratory muscle strength. The Bland-Altman plot was used to investigate the agreement between observed and predicted 6MWDs.

Results: Significant positive correlations were found between 6MWD and forced vital capacity (FVC)_%predicted (r = 0.528, P = 0.022) and maximum inspiratory pressure (MIP)_%predicted (r = 0.640, P = 0.022). Age (r = -0.350, P = 0.008) and body mass index (BMI) (r= -0.561, P < 0.001) were negatively correlated with 6MWD. The best regression model included MIP_%predicted (β = 0.332, P = 0.002), BMI (β = -0.264, P = 0.012), being male (β = 0.262, P = 0.003), age (β = -0.210, P = 0.020), and FVC_%predicted (β = 0.219, P = 0.026) as significant unique contributors. The final multiple linear regression model was significant [F (5, 50) = 19.08, P < 0.001] and explained 65.6% of the variance (R² = 0.656) in the 6MWD.

Conclusion: Lung function and respiratory muscle strength significantly contribute to functional exercise capacity in post-MI. This study emphasizes the importance of comprehensive respiratory function assessments in rehabilitation strategies to improve exercise capacity in patients with post-MI.