1740 LARYNGEAL MUSCLE ACTIVITY REGULATES EXPIRATORY FLOW A AND LUNG VOLUME

Abstract

In neonatal and adult animals, abduction of the vocal cords by laryngeal muscles regulates airflow by decreasing inspiratory and expiratory airway resistance. To determine if laryngeal muscles modify airflow in neonates, we recorded electromyograms (EMG) in the posterior laryngeal area(LAR) with electrodes attached to the tip of an esophageal catheter inserted 7-9cm beyond the nares. Simultaneous diaphragm(DIA) EMG was recorded from surface electrodes and airflow via mask pneumotachograph. Studies were performed in 12 healthy preterm infants(birthweight 1.6 ±.4kg, gestational age 32±2 weeks, postnatal age 21±8 days) without respiratory distress. Bursts of LAR EMG preceded onset of both DIA EMG and inspiratory airflow by 66±58msec(p<0.05) and 175±75msec(p<0.001), respectively. Retarded expiratory flow during early expiration(expiratory breaking) was observed in 9 infants. Onset of LAR EMG during late expiration in these subjects coincided with development of high end expiratory airflow and exhalation of 3-13cc of air. Thus, laryngeal breaking maintained an increased lung volume throughout most of expiration. In contrast, high flow throughout expiration(absence of breaking) coincided with increased expiratory LAR EMG. We conclude that laryngeal muscle activity regulates respiratory airflow. Control of laryngeal muscle activity maintains an elevated lung volume until end expiration in healthy preterm infants and may assume even greater importance in neonates with decreased functional residual capacity. NIH HL 31173 and HL25830