INFERIOR PHARYNGEAL CONSTRICTOR ELECTROMYOGRAPHIC ACTIVITY DURING PERMEABILITY PULMONARY-EDEMA IN LAMBS

Newborn mammals exhibit an active expiratory upper airway closure duri ng the first hours of extrauterine life. We have recently shown that p ermeability pulmonary edema led to active expiratory glottic closure i n awake newborn lambs while hypoxia (inspired O-2 fraction 8%; 15 min) did not. In the present study, we tested the hypothesis that expirato ry glottic closure was accompanied by an increase in pharyngeal constr ictor muscle expiratory electromyographic (EMG) activity. We studied s even awake nonsedated lambs aged 8-20 days. Airflow (facial mask + pne umotachograph), blood gases (arterial catheter), and EMG activity of b oth the thyroarytenoid muscle (a glottic adductor) and the inferior ph aryngeal constrictor muscle were recorded before and after intravenous injection of halothane (0.05 ml/kg) to induce a permeability pulmonar y edema. A central apnea (duration 15 s to 5 min) with continuous thyr oarytenoid and inferior pharyngeal constrictor activity was observed w ithin seconds after halothane injection. One lamb died despite rescuin g maneuvers. An expiratory phasic thyroarytenoid and inferior pharynge al constrictor muscle activity with simultaneous zero airflow graduall y took place and, by 30 min after halothane injection, was present at each expiration in the six remaining lambs. Expiratory glottic and pha ryngeal constrictor muscle EMG activity was subsequently present durin g the whole study period (1.5-5 h), even after correction of the initi al hypoxia. Permeability lung edema was present at postmortem examinat ion in all seven lambs. We conclude that a permeability pulmonary edem a induced by intravenous halothane in nonsedated lambs enhances both g lottic and pharyngeal constrictor muscle expiratory EMG. We hypothesiz e that expiratory contraction of the inferior pharyngeal constrictor m uscle could participate in the active expiratory upper airway closure; this, in turn, might improve alveolocapillary gas exchange by increas ing the end-expiratory lung volume.