1671A RESPIRATORY FAILURE AND THE EXPIRATORY CONTROL OF BREATHING IN LAMBS

Abstract

During quiet sleep (QS) in lambs phasic laryngeal adduction (Thyroarytenoid TA) is sufficient to elevate subglottic pressure to 10 cms H2O. This does not occur in active sleep (AS).Present studies using chronically implanted emg electrodes, air flow and pressure measurements were to determine the contribution of the upper airway (larynx), and the diaphragm on the maintenance of lung volume and respiratory drive. In QS respiratory frequency (RF) fell from 8 days to 32 days postnatal age [91±11 to 31±3 breaths min] and was related to an increase in expiratory time (TE). Subglottic pressure, expiratory laryngeal resistance and integrated TA emg activity correlated well with TE.The diaphragm did not contract uniformly; up to 45% of the contraction time of the vertebral diaphragm was expiratory whereas the paratendinous diaphragm contraction ceased at end-inspiration. Removing the positive airway pressure during expiration by opening a tracheotomy caused 1) an increase in expiratory laryngeal adduction and in expiratory activity of the diaphragm; 2) a fall in respiratory frequency. Since vagal blockade had the same effect, pulmonary vagal pressure-sensitive afferents control the laryngeal adductors and the expiratory activity of the diaphragm. Preventing expiratory resistance to airflow during QS leads, to a loss of RF, lung volume and sometimes respiratory failure, overriding the normal chemical drive to breathing. This finding may relate to future sleep-related respiratory failure. FSSID NO. 26.