COMPETITION BETWEEN GAS-EXCHANGE AND SPEECH PRODUCTION IN VENTILATED SUBJECTS

Competition between airflow requirements for speaking and gas exchange occurs in ventilator-dependent tracheotomized subjects who can 'steal ' air from alveolar ventilation during the ventilator's inflation phas e to produce sound. We wondered whether these subjects adopted strateg ies to minimize hypoventilation when speaking, particularly when venti latory drive and respiratory discomfort are increased by hypercapnia. We recorded speech and ventilatory and speaking volumes in five ventil ated subjects during reading and extemporaneous speech. All subjects s poke during the ventilator's inflation (and expiratory) phase, losing approximately 15% of their inspired tidal volume. During induced hyper capnia (IS mmHg increase in Petco(2)) which caused shortness of breath , all subjects could still speak adequately, Two subjects 'adapted' to hypercapnia by reducing the air used for speaking during inflation. I n contrast, one subject reacted, as normal subjects do, by increasing the airflow per syllable (a mal-adaptive strategy in ventilated subjec ts). These changes were modest despite the strong hypercapnic stimulus . (C) 1998 Elsevier Science B.V. All rights reserved.