Spirometer‐dependence of vital capacity in ALS: Validation of a portable device in 52 patients.

Since the evaluation of vital capacity (VC) needs to be carried out every three months in patients with amyotrophic lateral sclerosis (ALS), a portable spirometer would be of value in clinical practice. Over the follow‐up of 52 ALS patients, we compared the values of slow vital capacity measured by two spirometers: a reference flow‐metered spirometer based on a Hans‐Rudolph pneumotachograph and a portable Venturi spirometer. The objectives were to analyse the overall concordance of the measurements from the two devices and determine a discordance cut‐off. The correlation between measurements was high ( r = 0.936) and significant ( p -20 ). Bland and Altman analysis showed that the measurements were concordant at a statistical risk of 5%; nevertheless, on examination of the raw differences between the measurements, two sub‐populations could be identified on either side of the 56% cut‐off where the means of the differences were significantly different ( p [ABSTRACT FROM AUTHOR]