Effect of hypoxia on laryngeal reflex apnea--implications for sudden infant death.

Apnea was elicited by the application of chemical stimuli to the laryngeal region of 25 piglets from 1 to 70 days of age. Animals were tested under normoxic and hypoxic (Flo2 10%) conditions with water and solutions of graded acid and salt concentration. The chemoreflex was found to diminish with postnatal age. Fatal apneic episodes were confined to animals less than 3 weeks of age. Hypoxia consistently augmented the reflex, and in some cases elicited fatal apnea in animals that had survived similar stimulation under normoxic conditions. A direct relationship was also found between the strength of stimulus and respiratory response. Apnea increased with diminishing NaCl concentration or pH. The reflex was abolished by bilateral section of the superior laryngeal nerves. Fatal apnea elicited by laryngeal chemo-stimulation under the circumstance of hypoxia may provide further insight into the enigma of sudden infant death.