How Respiratory Muscle Strength Correlates with Cough Capacity in Patients with Respiratory Muscle Weakness

Abstract

Purpose: The purpose of this study is to investigate how respiratory muscle strength correlates to cough capacity in patients with respiratory muscle weakness. Materials and Methods: Forty-five patients with amyotrophic lateral sclerosis (ALS), 43 with cervical spinal cord injury (SCI), and 42 with Duchenne muscular dystrophy (DMD) were recruited. Pulmonary function tests including forced vital capacity (FVC) and respiratory muscle strength (maximal expiratory pressure, MEP; maximal inspiratory pressure, MIP) were performed. The correlation between respiratory muscle strength and cough capacity was analyzed. Results: In the SCI group, FVC in a supine position ($2,597{\pm}648$ mL) was significantly higher than FVC in a sitting position ($2,304{\pm}564$ mL, p < 0.01). Conversely, in the ALS group, FVC sitting ($1,370{\pm}604$ mL) was significantly higher than in supine ($1,168{\pm}599$ mL, p < 0.01). In the DMD group, there was no statistically significant difference between FVC while sitting ($1,342{\pm}506$ mL) and FVC while supine ($1,304{\pm}500$ mL). In addition, the MEP and MIP of all three groups showed a significant correlation with peak cough flow (PCF) (p < 0.01, Pearson s correlation analysis). In the SCI group, MIP was more closely correlated with PCF, while in the ALS and DMD groups, MEP was more closely correlated with PCF (p < 0.01, multiple regression analysis). Conclusion: To generate cough flow, inspiratory muscle strength is significantly more important for SCI patients, while expiratory muscle function is significantly more important for ALS and DMD patients.

Keywords

• Amyotrophic lateral sclerosis;
• muscular dystrophy;
• duchenne;
• respiratory function tests;
• spinal cord injuries