Predictors of ineffective cough during a chest infection in patients with stable amyotrophic lateral sclerosis

Rationale: In patients with neuromuscular diseases, a chest infection is associated with a reduction in respiratory muscle function that may result in decreased cough effectiveness. Objectives: To determine if a clinical or functional parameter in patients with amyotrophic lateral sclerosis (ALS) in a stable condition could predict spontaneous cough ineffectiveness during a respiratory tract infection. Methods: Forty consecutive patients with ALS referred to our Respiratory Care Unit were studied during a one-year follow-up. Measurements and Main Results: FEV1, FVC, FEV1/FVC, peak cough flow (PCF), peak velocity time (PVT), maximum inspiratory and expiratory pressures, and bulbar dysfunction evaluation using the Norris scale bulbar subscore (NBS). A total of 26 patients (65%) had spontaneous cough ineffectiveness during a respiratory tract infection. The best variables to predict nonassisted cough during a respiratory tract infection were NBS (p < 0.01) with a cutoff point of 29 (sensitivity, 0.89; specificity, 0.90; positive predicted value, 0.88; negative predictive value, 0.87), PCF (p < 0.001) with a cutoff point of 4.25 L/s (sensitivity, 0.74; specificity, 0.85; positive predictive value, 0.71; negative predictive value, 0.85), and PCF/PVT (p < 0.001) with a cutoff point of 28.88 L/s(2) (sensitivity, 0.77; specificity, 0.96; positive predictive value, 0.91; negative predictive value, 0.89). Conclusions: In patients with stable ALS, bulbar dysfunction (NBS < 29), PCF I(< 4.25 L/s), and PCF/PVT (< 28.88 L/s(2)) could predict the risk of ineffective spontaneous cough during a respiratory tract infection.