Nancy M. Bauman MD, Anthony D. Sandler MD, Timothy M. McCulloch MD
Michael P. Porter, Richard J.H. Smith MD

The laryngeal chemoreflex (LCR) and the esophagolaryngeal adductor reflex (ELAR) share important similarities in their age dependency and possible role in sudden infant death syndrome and apparent life-threatening events. The LCR is characterized by central apnea, hypotension, and bradycardia following the application of water to the laryngeal mucosa. The ELAR is characterized by obstructive apnea, hypertension, and tachycardia following stimulation of sensory nerves in the distal esophagus. We recently determined that substance P is a key neurotransmitter in the ELAR and that its systemic antagonist blocks the reflex. Because the two reflexes share a similar age dependency, this study was designed to determine the role of substance P in the LCR. The reflex was elicited in 6 piglets between 2 and 10 weeks of age, and systemic and laryngeal responses were monitored. Pretreatment with systemic substance P antagonist did not significantly alter the apnea response or associated systemic changes. This confirms that although the LCR and ELAR share a similar age dependency, they are independent reflexes with distinct systemic responses and dissimilar key neurotransmitters.