Background: Serial measurements of pulmonary function to indicate decreasing respiratory muscle strength in patients with amyotrophic lateral sclerosis (ALS) is well documented. Quantitative outcome measures include declining FVC, FEV1, maximal inspired pressure, maximal expired pressure, and maximal voluntary ventilation. Increasing peak expiratory flow time (PEFT) may represent a further sensitive measure of declining respiratory muscle strength in ALS.
Methods: Fifty-five patients with ALS performed flow-volume loops serially after presentation. The percentage change from baseline values for FVC, peak expiratory flow (PEFR), and PEFT were compared using Spearman correlation coefficients. The prolongation of PEFT with serial tests was analyzed using a Kruskal-Wallis with a Dunn multiple comparison test. Bulbar-onset and limb-onset PEFT was compared using the Mann-Whitney test.
Results: PEFT was significantly increased from baseline values at all follow-up tests. However, PEFTs measured at the third, fourth, fifth, and sixth visits, although higher, were not significantly different. Significant negative correlations existed between the increase in PEFT and the decrease in PEFR and FVC. Significant positive correlations existed between the increase in PEFT and days from diagnosis and the decrease in PEFR and decrease in FVC.
Conclusion: PEFT increases significantly and linearly with time in patients with ALS and may begin to plateau with bulbar symptoms. PEFT increases at a faster rate than the rate of decline in both FVC and PEFR. PEFT is a quantitative measure of decreasing pulmonary function in ALS that is easily measured.