THE ROLE OF THE UPPER AIRWAY IN CONTRIBUTING TO RESPIRATORY RESPONSESDURING EXPERIMENTAL SEIZURES IN PIGLETS

Recent data demonstrating stimulation of respiration during seizures a re at odds with the frequent clinical finding of respiratory impairmen t in patients with generalized seizures. To determine the role of the upper airway in contributing to these clinical observations, a study w as performed in 12 weanling piglets. An arterial catheter and epidural electrodes were placed in ketamine-anesthetized piglets. In intact pi glets, all airflow was measured through a snug-fitting nasal mask wher eas pressure was measured with a subglottic catheter. Tracheostomized piglets had airflow and pressure measured at the trachea. Seizures wer e induced with i.v. injections of pentylenetetrazol. Peak inspiratory flow resistance was calculated by averaging three epochs of five to se ven consecutive breaths. Epochs of greater than 20 s in duration with a tidal volume of <10 mt were termed apnea. Apnea was considered centr al when airway pressure was >-2cm H2O and obstructive when <-10 cm H2O . After 20 min of untreated seizures, intact piglets had significant r espiratory and metabolic acidosis, whereas tracheostomized piglets had significant increases in Ve and mild metabolic acidosis. Apnea and ob struction were observed frequently in intact piglets. Resistance was u nchanged during seizures in tracheostomized piglets, whereas a nearly 4-fold increase in inspiratory resistance was observed in intact pigle ts. We conclude that upper airway patency and resistances are importan t determinants of respiratory responses during generalized seizures in piglets.