Spirometry in the supine position improves the detection of diaphragmatic weakness in patients with amyotrophic lateral sclerosis.
OBJECTIVE
To determine which respiratory function tests best predicted diaphragmatic strength in patients with amyotrophic lateral sclerosis.


METHODS
Patients referred for pulmonary evaluation were included (n = 25) if they underwent measurement of transdiaphragmatic pressure (Pdi) and one or more of the following on the same day: upright FVC, supine FVC, upright FEV(1), supine FEV(1), maximal inspiratory pressure (MIP), maximal expiratory pressure (MEP), and PaCO(2). Abdominal paradox and use of accessory muscles were also assessed. Bivariate analyses were performed using simple linear regression. Sensitivity and specificity of the potential predictors to detect an abnormal Pdi (< 70 cm H(2)O) were calculated.


METHODS
Pulmonary function laboratory of an academic medical center.


RESULTS
Upright FVC, FEV(1), and MEP were all significantly correlated with Pdi, while MIP and PaCO(2) were not. Supine FVC was the most highly correlated predictor of Pdi (R(2) = 0.76). A cutoff of supine FVC that was < 75% predicted was 100% sensitive and specific for predicting an abnormally low Pdi. Accessory muscle use and abdominal paradox were both significantly associated with Pdi, and the presence of accessory muscle use had a sensitivity of 84% and a specificity of 100% for detecting a low Pdi.


CONCLUSIONS
Our findings suggest that supine FVC is an excellent and simple test of diaphragmatic weakness.
Lechtzin
Noah
N
Department of Medicine, Division of Pulmonary and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA. nlechtz@welch.jhu.edu
Wiener
Charles M
CM
Shade
David M
DM
Clawson
Lora
L
Diette
Gregory B
GB
D000328:Adult; D000368:Aged; D000690:Amyotrophic Lateral Sclerosis / Q000503:physiopathology*; D003964:Diaphragm / Q000503:physiopathology*; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D008875:Middle Aged; D011312:Pressure; D013147:Spirometry; D014797:Vital Capacity