A complete active glottal closure in inspiratory position is present throughout 90% of central apneas in the preterm newborn lamb, partly preventing the post-apneic desaturation. However, results of the literature (Hutchison A, 2002) suggest that some induced neonatal apneas are characterized by an active laryngeal opening by contraction of the dilator muscles of the larynx. Thus, the goal of this study is to test the hypothesis that the larynx is actively open during some induced and spontaneous central apneas in newborn lambs.
Ten full-term lambs were chronically instrumented for recording electroencephalogram, eye movements, electrocardiogram, SaO2, nasal flow, subglottal pressure. In addition, the electrical activity (EMG) of the diaphragm, a laryngeal constrictor (thyroarytenoid muscle, TA, n = 4) and two laryngeal dilators (cricothyroid muscle, CT, n = 7 and posterior cricoarytenoid muscle, PCA, n = 7) was recorded. Polysomnographic recordings were performed in non-sedated lambs, using our custom-made radiotelemetry system to study both induced and spontaneous apneas on two different occasions.
The results show a continuous TA EMG throughout 73% of all induced central apneas, and during the first two thirds of 89% of all spontaneous central apneas (mostly after a sigh). TA EMG was interrupted by CT EMG alone or with PCA EMG in 13% of all spontaneous and induced central apneas. The presence of the CT and/or PCA EMG during induced central apneas was consistently associated with both a fall of the subglottal pressure to atmospheric pressure and a decrease in lung volume below the preceding end-expiratory lung volume.
In conclusion, a few central apneas in newborn lambs are characterized by both an active closure and opening of the larynx, occurring sequentially.
Active opening of the glottis is associated with a fall of the subglottal pressure, which consequently leads to a decreased in lung volume during central apnea.
Nathalie Samson, None.