• Ross K Morgan, Stephen McNally, Michael Alexander, Ronan Conroy, Orla Hardiman, and Richard W Costello.
• Department of Medicine, Royal College of Surgeons in Ireland, Beaumont Hospital, Dublin 9, Ireland.
• Am. J. Respir. Crit. Care Med. 2005 Feb 1; 171 (3): 269-74.

AbstractRespiratory 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 H(2)O was significantly related with nocturnal hypoxemia. When sniff nasal-inspiratory force was less than 40 cm H(2)O, 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 H(2)O 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.

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