Multiple respiratory assessment and thresholds for noninvasive ventilation in adult patients with spinal muscular atrophy

This study aimed to examine feasibility of inspiratory muscle strength tests, such as maximal inspiratory pressure (MIP) and sniff nasal inspiratory pressure (SNIP) in adult patients affected by spinal muscular atrophy (SMA), as well as their ability, along with forced vital capacity (FVC), to predict noninvasive ventilation (NIV) needs. Additionally, we evaluated feasibility and effectiveness of respiratory oscillometric measurements in the same patients. Twenty patients were retrospectively evaluated. NIV requirement was considered as peak nocturnal transcutaneous PCO2 > 49 mmHg, according to the cut-off used by Ward et al. MIP and SNIP were feasible in all patients. SNIP had significantly higher values (p < 0.001) and poorly agreed with MIP. ROC analysis revealed MIP as a weak predictor for NIV initiation (AUC = 0.57), while FVC (AUC 0.78, best cut-off 20% of predicted) and SNIP (AUC 0.84, best cut-off 61 cmH2O) were more effective. Oscillometry was performed in 11 patients. Reactance was abnormal in six of them and was significantly correlated with FVC (ρ = 0.70, p = 0.01) and SNIP (ρ = 0.72, p = 0.007), but not with MIP. In adult SMA patients, both MIP and SNIP are feasible, but SNIP is a better predictor of NIV needs, similar to FVC. Optimal predictive thresholds differed from those previously observed in neuromuscular disease. Oscillometric measurements may help to estimate FVC and SNIP in poorly collaborating patients.