Using phonation time to estimate vital capacity in amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a neuromuscular disease in which progressive respiratory weakness is usually the proximate cause of death. Since continued assessment of respiratory function is important in predicting progression, phonation time was measured in a group of 41 ALS patients and correlated with measured vital capacity. The findings show that the variance in phonation time accounts for nearly 50% of the variability of vital capacity, and therefore, successive measurements of phonation time are a useful means of estimating the loss of vital capacity.