Laryngeal reflex inhibition of breathing in piglets: influences of anemia and catecholamine depletion.

Laryngeal reflex inhibition of breathing was studied in 31 piglets of both sexes varying in age from 34 to 93 days. Continuing supramaximal electrical stimulation of one superior laryngeal nerve (SLN) was associated with spontaneous resumption of breathing within 1 min in animals more than 1 mo of age. Respiratory rate and depth were reduced, however. In contrast with normal piglets, electrical stimulation of the SLN in those with severe anemia (Hct = 8.0 +/- 0.5%) caused extended apnea. An intermediate effect was observed in animals with normal hematocrits but given reserpine (2 mg/kg) 2 days prior to study. The apnea response was potentiated in these animals by reduction of the hematocrit from 22.8 +/- 3.4% to 8.4 +/- 1.1% by hemodilution. In normal piglets similar degrees of hemodilution had no discernible effects; An interrelationship between oxygen availability, adrenergic activity, and SLN-induced respiratory depression in young piglets is suggested by these findings.