Measuring vital capacity in amyotrophic lateral sclerosis: Effects of interfaces and reproducibility.
BACKGROUND
Deterioration of vital capacity (VC) in amyotrophic lateral sclerosis (ALS) signifies disease progression and indicates need for non-invasive ventilation. Weak facial muscles consequent to ALS, with resulting poor mouth seal, may interfere with the accuracy of VC measurements.


OBJECTIVES
To determine whether different interfaces affect VC measurements in ALS patients and whether the interface yielding the largest VC produces an even higher VC when re-measured after one week (learning effect). To explore the relationship between optimal interface VC and sniff nasal pressure (SNIP), a measurement of global inspiratory muscle strength.


METHODS
Thirty-five patients (17 bulbar and 18 spinal ALS) were studied. Three interfaces (rigid-cylindrical, flanged, oronasal mask) were tested. One week after the first visit, VC was recorded using the optimal interface. SNIP recordings were also obtained.


RESULTS
In the bulbar ALS group, median (interquartile range) VC with the flanged mouthpiece was 8.4% (3.9-15.5) larger than with the cylindrical mouthpiece (p < 0.001). VC values with oronasal mask were intermediate to VC with the other two interfaces. In spinal ALS, flanged mouthpiece VC was 4.6% (2.3-7.5) larger than with oronasal mask (p < 0.0006). The latter was 4.5% (0.6-5.2) smaller than with the cylindrical mouthpiece (p = 0.002). In both groups, VC during the second visit was greater than during the first visit (p < 0.025). SNIPs were logarithmically related to VC values recorded with the flanged mouthpiece.


CONCLUSION
A flanged mouthpiece yields the largest values of VC in patients with bulbar and spinal ALS.
['Pellegrino|Giulia Michela|GM|', 'Sferrazza Papa|Giuseppe Francesco|GF|', 'Centanni|Stefano|S|', 'Corbo|Massimo|M|', 'Kvarnberg|David|D|', 'Tobin|Martin J|MJ|', 'Laghi|Franco|F|']
D000368:Aged D000690:Amyotrophic Lateral Sclerosis D005260:Female D006801:Humans D008297:Male D008875:Middle Aged D053580:Muscle Strength D009296:Nasal Cavity D011312:Pressure D015203:Reproducibility of Results D012129:Respiratory Function Tests D012132:Respiratory Muscles D012680:Sensitivity and Specificity D014797:Vital Capacity
Amyotrophic lateral sclerosis Non-invasive ventilation Oral interfaces Respiratory function Respiratory function test Respiratory muscle weakness