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1 Pulmonary Research Unit and Departments of 2 Pediatrics and 3 Surgery, Université de Sherbrooke, Québec, Canada J1H 5N4
The present study was undertaken to gain further
insight into the mechanisms responsible for the sustained active
expiratory upper airway closure previously observed during
high-permeability pulmonary edema in lambs. The
experiments were conducted in nonsedated lambs, in which airflow and
thyroarytenoid and inferior pharyngeal constrictor muscle
electromyographic activity were recorded. We first studied the
consequences of hemodynamic pulmonary edema (induced by impeding
pulmonary venous return) on upper airway dynamics in five lambs; under
this condition, a sustained expiratory upper airway closure
consistently appeared. We then tested whether expiratory upper airway
closure was related to vagal afferent activity from bronchopulmonary
receptors. Five bivagotomized lambs underwent high-permeability
pulmonary edema: no sustained expiratory upper airway closure was
observed. Finally, we studied whether a sustained decrease in lung
volume induced a sustained expiratory upper airway closure. Five lambs
underwent a 250-ml pleural infusion: no sustained expiratory upper
airway closure was observed. We conclude that
1) the sustained expiratory upper
airway closure observed during pulmonary edema in nonsedated lambs is
related to stimulation of vagal afferents by an increase in lung water and 2) a decrease in lung volume
does not seem to be the causal factor.
control of breathing; lung volume; newborn; vagus nerve; thyroarytenoid muscle; inferior pharyngeal constrictor muscle
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