Late Breaking Abstract - Measurement of Vital Capacity in Amyotrophic Lateral Sclerosis: Methodological Aspects

Background: In amyotrophic lateral sclerosis (ALS) deterioration of vital capacity (VC) is a marker of disease progression and a criterion to start non-invasive ventilation. Yet lack of mouth seal as a result of facial muscle weakness or inadequate patient cooperation may bias VC measurements. Aim: To test whether measurements of VC are affected by different oral interfaces and are repeatable over time. Methods: Ten ALS patients, four of whom with bulbar dysfunction, were enrolled in this QI project. In random order, three different interfaces currently used in pulmonary function tests labs (rigid cylindrical mouthpiece, flanged mouthpiece, and oronasal mask) were tested. Patients performed 3 to 8 VC maneuvers with each interface. Results: VC was greater with the flanged mouthpiece (2.52 ± 0.25 L) than with oronasal mask (2.30 ± 0.24 L) or with the rigid cylindrical mouthpiece (2.29 ± 0.24 L) (p<0.01, ANOVA). Measurements were repeated one week later with the mouthpiece that yielded the greatest VC values during the first visit. VC values during this second visit were 0.25 ± 0.09 L greater than the VC values during the first visit (p<0.05, paired t-test). Conclusion: In most patients with ALS, the use of a flanged mouthpiece yielded significantly greater VC values than oronasal mask or rigid mouthpiece. In addition, a second round of measurements a week later led to significantly higher value of VC. These findings have the potential to impact monitoring of disease progression and clinical decisions in patients with ALS. Support: Veterans Administration VAH Hines, USA; University of Milan, Italy; Casa di Cura del Policlinico, Milan, Italy.