GLOTTAL PATENCY DURING EXPERIMENTAL SEIZURES IN PIGLETS

Tracheostomized cats and piglets demonstrate respiratory stimulation d uring experimental seizures, whereas airway intact piglets demonstrate hypoventilation and increased subglottic resistances. The purpose of this study was to characterize the role of the vocal folds in contribu ting to these increased subglottic resistances during experimental sei zures. A controlled animal study was performed in six anesthetized, sp ontaneously breathing, hyperoxic piglets who had subglottic pressure a nd airflow measured. A fiberoptic video scope directed into the cephal ad trachea recorded subglottic images of the vocal folds. Glottal area patency (GAP) was evaluated at inspiratory onset (I-o), peak inspirat ory pressure (I-p), and expiratory onset (E(o)) for four to five conse cutive breaths under baseline control, ictal, interictal, and anticonv ulsant conditions. Seizures were induced with i.v. pentylenetetrazol o r bicuculline. Normalized GAP was greatest at I-p under all conditions , except anticonvulsant. During ictal periods, piglets demonstrated si gnificant reductions in mean GAP throughout the respiratory cycle (I-o , 98%; I-p, 78%; E(o), 98%), compared with baseline (p < 0.001, repeat measures analysis of variance). During ictal discharges, hypoventilat ion and glottal obstruction resulted in significant reductions in mean arterial pH (-0.35) and PaO2 (-39 kPa) and elevations in PaCO2 (+8.1 kPa), compared with baseline conditions. During interictal conditions mean GAP at I-p was increased, whereas at E(o) (-66%) GAP was reduced, compared with control. These data demonstrate that the vocal folds ar e tonically adducted throughout the respiratory cycle during ictal pha ses and have increased expiratory adduction during interictal phases o f seizures induced with standard i.v. convulsants in hyperoxic piglets .