COORDINATION BETWEEN GLOTTIC ADDUCTOR MUSCLE AND DIAPHRAGM EMG ACTIVITY IN FETAL LAMBS IN-UTERO

It has previously been reported that; active glottic adduction is pres ent during prolonged apneas but absent during periods of breathing mov ements in fetal lambs in utero. The present study was aimed at examini ng the precise coordination between fetal breathing movements [diaphra gm electromyographic (EMG) activity (Di EMG)] and glottic adduction [t hyroarytenoid muscle EMG activity (TA EMG)]. Electrodes for electroenc ephalogram,, eye movements, TA EMG, and Di EMG and an arterial cathete r were surgically implanted in fetal lambs 123-142 days postconception . Polygraphic recordings were performed without sedation while the ewe breathed room air (n = II) or various gas mixtures (hypoxia, n = 5; h yperoxia, it = 4; hypercapnia, it = 5; hypercapnia + hyperoxia, n = 5) . Tonic TA EMC was observed throughout >90% of apneas (>6 s) in both n on-rapid-eye-movement and rapid-eye-movement sleep, and when Di EMG fr equency decreased in rapid-eye-movement sleep. In all but two fetuses, TA EMG was immediately inhibited when Di EMG appeared. Altering blood gases did not modify these results. In conclusion, Di EMG and TA EMG are well coordinated in late gestation in fetal lambs, except in a few cases. These findings may have consequences for understanding the pat hogenesis of mixed/obstructive apneas of prematurity.