Objective: To determine under what circumstances the use of mechanical insufflation-exsufflation (MI-E) can generate clinically effective expiratory flows for airway clearance (> 2.7 L/s) for clinically stable patients with amyotrophic lateral sclerosis (ALS).
Materials and method: Twenty-six consecutive patients with ALS were studied, 15 with severe bulbar dysfunction. Using a pneumotachograph and with the aid of an oronasal mask, we measured FVC, FEV1, peak cough flow (PCF), maximum insufflation capacity (MIC), PCF generated from a maximum insufflation MIC (PCFmic), and PCF generated by MI-E (PCFmi-e). MI-E was delivered at ± 40 cm H2O. Maximum inspiratory pressure (Pimax) and maximum expiratory pressure (Pemax) at the mouth were also measured.
Results: Although both groups had a similar time from ALS symptom onset to diagnosis, statistical differences (p < 0.05) were found between nonbulbar and bulbar patients in lung function and cough capacity parameters: FVC, 2.58 ± 1.24 L vs 1.62 ± 0.74 L; FEV1, 2.26 ± 1.18 L vs 1.54 ± 0.69 L; Pimax, – 93.45 ± 47.47 cm H2O vs − 3.64 ± 25.07 cm H2O; Pemax, 140.45 ± 75.98 cm H2O vs 69.93 ± 32.14 cm H2O; MIC, 3.02 ± 1.22 L vs 1.97 ± 0.75 L; PCF, 5.91 ± 2.55 L/s vs 3.42 ± 1.44 L/s; PCFmic, 6.68 ± 2.71 L/s vs 4.00 ± 1.48 L/s; and PCFmi-e, 4.34 ± 0.82 L/s vs 3.35 ± 0.77 L/s. Four patients with bulbar dysfunction and MIC > 1 L had PCFmi-e < 2.7 L/s. The receiver operating characteristic (ROC) curve analysis showed PCFmic of ≤ 2.7 L/s predicting those patients with PCFmi-e < 2.7 L/s. The ROC curve analysis showed PCFmic > 4 L/s predicting those patients with PCFmic greater than PCFmi-e.
Conclusion: MI-E is able to generate clinically effective PCFmi-e (> 2.7 L/s) for stable patients with ALS, except for those with bulbar dysfunction who also have a MIC > 1 L and PCFmic <2.7 L/s who probably have severe dynamic collapse of the upper airways during the exsufflation cycle. Clinically stable patients with mild respiratory dysfunction and PCFmic > 4 L/s might not benefit from MI-E except during an acute respiratory illness.