Dynamics of the chest wall during speech production: function of the thorax, rib cage, diaphragm, and abdomen.

Anteroposterior diameters of the rib cage and abdomen and esophageal and gastric pressures were measured in normal subjects in upright and supine body positions during respiratory maneuvers and utterance tasks. Data were charted in relative motion diagrams and various motion-pressure diagrams which enabled graphic solution for muscular pressures exerted by the chest wall and individually by the thorax, rib cage, diaphragm, and abdomen during utterances. Behaviors of the chest wall and its parts were found to depend upon lung volume, utterance loudness, body position, and utterance task. For utterances encompassing most of the vital capacity, chest wall effort was at first net inspiratory and later net expiratory. The former was governed predominately by the rib cage and the abdomen in the upright body position and by the diaphragm in the supine position. For conversational speech, chest wall effort was continuously expiratory, control being vested in the rib cage and the abdomen in the upright body position and typically in the rib cage alone in the supine position. Mechanisms operating during the utterances are discussed, particularly those involved with conversational speech production. We conclude that the abdomen occupies an especially important role in running conversational speech in that it mechanically tunes the diaphragm to increase the latter's inspiratory efficiency and thus enables man to minimally interrupt his ongoing speech for needed inspiratory pauses. We also discuss the relevance of our findings to clinical endeavors.