955 LARYNGEAL INDUCED APNEA IN THE CHEMODENERVATED PIGLET

Abstract

Laryngeal instillation of certain fluids in the piglet elicits reflex apnea, bradycardia, and hypertension. Chemosensitive receptors at the laryngeal entrance have their afferent pathway in the superior laryngeal nerve. Their stimulation may cause asphyxial death often in the newborn, but rarely in the older piglet. We studied the influence of the peripheral arterial chemoreceptors in modulating laryngeal responses in air-breathing pentobarbital-anesthetized newborn (N=9, age 7.0±0.9d) and older piglets (N=9, age 37.8±4.9d). The change in minute ventilation of exposure to 10% 02 in N2 was 19.3±10.6% (NS) in the newborn and 29.4±11.2% (p<.05) in the older piglets. Pure oxygen transiently depressed ventilation by 53.1±5.1% (p<.001) in the newborn and 51.4±6.3% (p<.001) in the older piglets, indicating that the peripheral chemoreceptors are fully active in the newborn. The duration of the net apnea (water minus saline) was similar in the intact newborn, 9.27±1.48 sec (p<.001) and older piglet,9.73±1.23 sec (p<.001). Carotid chemodenervation abolished the ventilatory response to oxygen but had negligible effect on the duration of laryngeal apnea. We conclude that recovery of spontaneous respiration after laryngeal induced apnea is independent of peripheral chemoreceptor activity. Our findings may have relevance to the clinical problem of sudden infant death, in which pathological abnormalities of the carotid body have recently been described.