Complete glottic closure during central apnea in lambs

Objective: The objectives of this study were threefold: to document complet e glottic closure during artificially induced central apnea in lambs; to un equivocally confirm that thyroarytenoid muscle electrical activity during c entral apneas in lambs reflects complete glottic closure; and to evaluate t he physiologic significance of this phenomenon in artificially induced cent ral apneas in lambs. Methods: We recorded thyroarytenoid (TA) muscle EMG, subglottic pressure, a nd lung volume simultaneously with direct endoscopic vision of the glottis from beneath on nine 11- to 15-day-old lambs during artificially induced ce ntral apneas. Results: Thirty-eight central apneas were induced. Complete glottic closure was present on 35/38 (92%) of these apneas. Complete glottic closure was a lways paralleled by thyroarytenoid muscle electromyogram (EMG) activity (35 /35). In no instance was TA EMG recorded without complete glottic closure. Moreover, positive subglottic pressure and maintenance of lung volume above functional residual capacity were observed in 27/30 (90%) and 18/19 (95%), respectively, of these apneas where complete glottic closure was present. Conclusions: Complete glottic closure is present throughout most artificial ly induced central apneas in lambs. Complete glottic closure is paralleled by TA EMG in artificially induced central apneas. Thyroarytenoid muscle ele ctromyographic activity is a reliable way to document complete glottic clos ure during apneas, especially in the presence of positive subglottic pressu re. These observations suggest that complete glottic closure could be a phy siologic mechanism aimed at maintaining higher lung volumes to improve gas exchange during central apneas.