Sniff nasal inspiratory pressure (SNIP) in amyotrophic lateral sclerosis: Relevance of the methodology for respiratory function evaluation

Objectives: We investigated two different methodological approaches for determining nasal inspiratory pressure during a sniff (SNIP) in patients with Amyotrophic Lateral Sclerosis (ALS). Patients and Methods: We included 37 ALS patients and 11 controls. SNIP was measured in the sitting position, performed in each nostril with (SNIPocclud) and without (SNIPopen) closing the contralateral nostril. The best of 3 consistent results was considered for analyses. Patients were also assessed with MIP and the revised functional ALS rating scale (ALSFRS-R). Mann-Whitney U test, Wilcoxon test and Spearman's rank correlation coefficient with Bonferroni correction were applied. Coefficient of variation (CV) was calculated. Results: SNIP was significantly lower in patients than controls, either for SNIPopen (p = 0.011) or SNIPocclud (p = 0.002). SNIPopen values were significantly lower both in ALS patients and controls than SNIPocclud (p < 0.001 and p = 0.007, respectively). SNIPopen CV was 8.14% and 8.51%, while SNIPocclud CV was 4.98% and 6.37%, respectively for controls and patients. SNIPopen and SNIPocclud were strongly correlated in both groups (r = 0.761 for controls; r = 0.768 for patients). In ALS, both methods were moderately correlated with MIP (respectively r = 0.525, p = 0.006 and r = 0.685, p < 0.001) and the respiratory subscore of ALSFRS-R (respectively r = 0.525, p = 0.001 and r = 0.64, p < 0.001). Although bulbar and spinal onset patients presented no differences for SNIPopen (p = 0.157), significant differences were found for SNIPocclud (p = 0.018). Conclusion: SNIPocclud should be considered when evaluating ALS patients as its values present lower variability and favor longer follow-up.