Effects of experimental cortical seizures on respiratory motor nerve activities in piglets

Airway obstruction at the level of the larynx causes respiratory insufficiency during experimental seizures in spontaneously breathing, anesthetized piglets (T. E. Terndrup and W. E. Fordyce, Pediatr. Res., 38: 61-66, 1995). To investigate further the neural mechanisms of this obstruction, the activities of the phrenic nerve (PH) and the recurrent laryngeal motor branches to the thyroarytenoid (TA) and posterior cricoarytenoid (PCA) muscles were analyzed in 11 anesthetized, vagotomized, paralyzed, and ventilated piglets. After a control recording period, seizures were induced by subcortical penicillin G injections. Compared with baseline conditions, nerve activities became irregular during seizures. Extraneous TA bursts during PH activation were evident in all piglets during seizures. During ictal phases of seizures, the peak integrated activities of the PH and the expiratory component of the PCA, but not TA or inspiratory PCA activities, were significantly decreased compared with interictal phases. During seizures, a significant delay in the onset of the inspiratory component of PCA activation with respect to the onset of the PH was observed. This study helps to explain respiratory impairment during cortical seizures by providing evidence of impaired timing of activation of laryngeal dilator mechanisms and coordination with those activating the diaphragm. Cyclical PH inhibition during high-intensity cortical discharges may provide a secondary mechanism producing respiratory insufficiency during seizures.