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Use of Sniff Nasal-Inspiratory Force to Predict Survival in Amyotrophic Lateral Sclerosis

Departments of Medicine, Neurology, and Epidemiology, Royal College of Surgeons in Ireland, Beaumont Hospital, Dublin, Ireland

Correspondence and requests for reprints should be addressed to Richard W. Costello, Department of Medicine, Royal College of Surgeons in Ireland, Beaumont Hospital, Dublin 9, Ireland. E-mail: rcostello{at}rcsi.ie

Respiratory muscle weakness is the usual cause of death in amyotrophic lateral sclerosis. The prognostic value of the forced vital capacity (FVC), mouth-inspiratory force, and sniff nasal-inspiratory force were established in a group of 98 patients with amyotrophic lateral sclerosis who were followed trimonthly for 3 years. Sniff nasal-inspiratory force correlated with the transdiaphragmatic pressure (r = 0.9, p < 0.01). Sniff nasal-inspiratory force was most likely to be recorded at the last visit (96% of cases), compared with either the FVC or mouth-inspiratory force (86% and 81%, respectively, p < 0.01). A sniff nasal-inspiratory force less than 40 cm H₂O was significantly related with nocturnal hypoxemia. When sniff nasal-inspiratory force was less than 40 cm H₂O, the hazard ratio for death was 9.1 (p = 0.001), and the median survival was 6 ± 0.3 months. The sensitivity of FVC < 50% for predicting 6-month mortality was 58% with a specificity of 96%, whereas sniff nasal-inspiratory force less than 40 H₂O had a sensitivity of 97% and a specificity of 79% for death within 6 months. Thus the sniff nasal-inspiratory force test is a good measure of respiratory muscle strength in amyotrophic lateral sclerosis, it can be performed by patients with advanced disease, and it gives prognostic information.

Key Words: noninvasive ventilation • respiratory failure • respiratory muscle strength

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