THE EFFECT OF ANTIHISTAMINES ON THE LARYNGEAL CHEMOREFLEX

The laryngeal chemoreflex (LCR) consists of ap nea, laryngospasm, and cardiovascular changes in neonates after laryngeal irritation and has been implicated in sudden infant death syndrome and apnea of infancy. Antihistamines attenuate a similar vagally mediated pulmonary chemoref lex. The intravenous antihistamine effect on the LCR was studied in ne onatal piglets. Laryngeal muscle activity, respiration, blood pressure , and pulse were measured during water stimulation of the LCR. After b aseline LCR recordings, intravenous diphenhydramine (2.5 mg/kg) or cim etidine (20 mg/kg) was bolused (control group received saline). LCR me asurements were repeated over 7 hours. Diphenhydramine significantly s hortened apneas (P<.05) 3 to 7 hours after drug bolus, which is believ ed to be secondary to central atropinic effects. Cimetidine demonstrat ed no attenuation of the LCR.