Periodic variation in inspiratory volume characterizes speech as well as quiet breathing.

Variability in inspired lung volume prior to speech is only partially accounted for by speech-related concerns such as the length and loudness of the planned utterance. Control mechanisms known to influence volume variability in non-speech breathing could potentially account for some of this variability, but only if they operate during speech as well. This investigation was designed to test for the presence of several such mechanisms during reading aloud. Lung volumes were recorded from 5 normal females as they read silently, then aloud. Inspired volumes were correlated with the volumes of the previous and following expirations and with inspiratory duration. Coefficients of variation were calculated for inspiratory volume, duration, and mean flow. Time-series analyses were used to compare periodicity in inspired volume for quiet and speech breathing. Control mechanisms operating during both quiet breathing and reading aloud included slow oscillations in inspired volume and minimized variability in mean flow. Inspired volume prior to speech was weakly but significantly correlated with preceding and following expired volume. It is concluded that some control strategies typical of quiet breathing contribute to volume variability in speech breathing.