Inspiratory muscle strength and walking capacity in patients with COPD

Purpose: It has been suggested that patients with inspiratory muscle weakness could benefit from specific inspiratory muscle training (IMT). We aimed to examine the frequency of patients with inspiratory muscle weakness in a Danish hospital-based outpatient pulmonary rehabilitation program, and to evaluate the association between inspiratory muscle strength and peripheral muscle strength and walking capacity. Methods: Maximal Inspiratory Pressure (MIP) was assessed in 97 patients with COPD (39 men, 58 women, mean age years 70 ± 9, forced expiratory volume in 1 s ((FEV₁) = 35 ± 10% pred.). The impact of MIP on knee-extension strength, walking distance, and symptom burden was evaluated using multiple linear regression analyses. Results: The MIP of the patients with COPD was 63 (95% CI 59; 67) cmH₂O and it was significantly reduced compared to gender and age-matched reference values 76 (95% CI 73; 79) cmH₂O (p < 0.001). Seven patients (7.2%) were under the lower limit of normal. MIP was negatively correlated with increasing age, female gender, decreasing knee-extension strength and lower FEV₁% pred. Walking distance was associated with knee-extension strength and it was not associated with MIP. Conclusion: Maximal inspiratory pressure was reduced in patients with COPD but only a few patients had a weak MIP. Whilst MIP was associated with leg muscle strength, it was not associated with walking distance or symptoms.