Chest
Clinical InvestigationsNeuromuscular DiseaseSpirometry in the Supine Position Improves the Detection of Diaphragmatic Weakness in Patients With Amyotrophic Lateral Sclerosis
Section snippets
Study Population
All ALS patients referred for pulmonary evaluation at a single academic medical center between December 1995 and June 2000 were considered for analysis. Patients were evaluated by neurologists and met the El Escorial definition of definite or probable ALS.13 Eligible patients had Pdi-sniff measured and at least one of the following tests performed on the same day: upright spirometry, supine spirometry, MIP, MEP, and Paco2. Pulmonary function tests were ordered for clinical indications, not as
Results
During the study period, 73 patients with ALS were referred for evaluation, of whom 25 patients (34.2%) had sufficient pulmonary function data for analysis. The patients who were not included in these analyses were similar to the reported patients with respect to age, gender, disease duration, mean FVC, and area of disease onset. The patient characteristics appear in Table 1 . The mean age was 61.4 years, and the majority of patients were male. The mean body mass index (BMI) was 24.5 ± 4.1 kg/m2
Discussion
This study shows that supine FVC is an accurate, noninvasive means to estimate Pdi-sniff. Combining two tests, supine FVC and MIP, is better than supine FVC alone. Our data show that supine FVC at < 75% predicted is very sensitive and specific for identifying diaphragmatic weakness, and we have also included a regression equation that can be used to estimate Pdi-sniff. The results of this study may allow for the substitution of a noninvasive measure of diaphragmatic strength for an invasive
ACKNOWLEDGMENT
We thank Dr. Peter Terry and Dr. Robert Wise for their encouragement and thoughtful reviews of earlier versions of this article.
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This research was supported by National Heart, Lung, and Blood Institute grant 2T32HL07534, and an Amyotrophic Lateral Sclerosis Association Clinical Management Research Grant.