Active expiratory glottic closure during permeability pulmonary edema in nonsedated lambs.

Abstract

It has long been claimed that the active expiratory glottic closure observed in newborns, especially during hyaline membrane disease, is related to hypoxia. However, we recently showed that hypoxia does not lead to active expiratory glottic closure in nonsedated lambs. In this study, we test the hypothesis that glottic closure is related to an excess of lung water present at birth. We studied 17 nonsedated lambs after inducing a permeability pulmonary edema via intravenous of either oleic acid (8 lambs) or halothane (9 lambs). We recorded airflow via a facial mask and pneumotachograph, as well as the electromyographic activity (EMG) of the thyroarytenoid muscle (TA), a glottic adductor. Blood gases were measured in 8 lambs via a brachial artery catheter. We identified laryngeal expiratory airflow braking on the breath-by-breath computed flow-volume loop and TA expiratory EMG as evidence of active expiratory glottic adduction. After the injection of oleic acid or halothane, an active expiratory glottic closure was recorded in all lambs but 1, usually throughout the recording period (60 to 300 min). The active expiratory glottic closure was not inhibited after correction of the hypoxia. We conclude that, in nonsedated lambs, a permeability pulmonary edema induces an active expiratory glottic closure. We hypothesize that the expiratory glottic closure commonly observed in newborns could help to ameliorate the alveolocapillary gas exchange by reopening the flooded alveoli.

Developmental changes in respiratory, febrile, and cardiovascular responses to PGE2 in newborn lambs

“…This study also shows for the first time that PGE 2 enhances expiratory TAEMG activity, thereby resulting in AF braking during expiration. Expiratory TAEMG activity in awake lambs is tonically inhibited by vagal afferents (39), but this activity can also be enhanced by vagal afferents in response to pulmonary deflation (17) or pulmonary edema (40). In the current study, the effect on TAEMG activity was greater during intracarotid than intrajugular infusion, and the augmentation of activity occurred within seconds after starting intracarotid infusion and thus before arterial blood gas tensions could change or significant edema could develop.…”

Effects of non-synchronised nasal intermittent positive pressure ventilation on spontaneous breathing in preterm infants

“…Therefore using diaphragmatic contraction to trigger NIPPV pressure rise does not guarantee an open glottis. In addition, newborn infants and animals commonly have laryngeal abduction during expiratory braking31 and central apnoeas32 to preserve lung volume and protect against desaturation. This would limit the effects of NIPPV by preventing the applied pressures reaching the chest.…”

Mechanisms of active laryngeal closure during noninvasive intermittent positive pressure ventilation in nonsedated lambs

“…Literature data have established that glottal constrictor muscles (e.g., TA muscles) are normally active during the postinspiratory phase of the breathing cycle. This serves to brake expiratory flow and delay lung emptying, a strategy especially used by the newborn in case of lung disease (14). A few studies, however, have reported that TA muscles can, at times, be active in inspiration.…”