Laryngeal Chemoreflex in Newborn Lambs: Respiratory and Swallowing Response to Salts, Acids, and Sugars

Abstract

Summary: The laryngeal chemoreflex was tested in a standardized manner in eighteen 1- to 6-day-old lambs. The respiratory and swallowing components of the reflex response to chemical solutions introduced to the larynx were quantified to characterize the function of the receptors and to elucidate what kind of receptors most likely are involved. A relationship between the strength of the stimulus and the respiratory response was found. The response was suppressed with the addition of small amounts of CaCl₂, NaCl, and LiCl. NaCl, 0.3-0.6 M, 0.15 M NaCl titrated to a pH of 3-5 with hydrochloric or acetic acid, and 0.25-1.0 M glucose in 0.15 M NaCl elicited the reflex response. A quantitative separation was seen in the respiratory response to equimolar concentrations of the salt solutions as well as to the acid solutions in normal saline with equal pH. The response to glucose was significantly reduced after application of potassium gymnemate (P < 0.001). A direct relationship between the amount of swallowing and the respiratory response was found (r = 0.83). The laryngeal chemoreflex responses to the stimuli used have certain functional characteristics that are similar to taste receptor responses. This would suggest that the taste bud-like structures present in the laryngeal area are likely receptors for mediation of the reflex. Speculation: Laryngeal chemoreflex apnea was elicited in newborn lambs with weak salt, acid, and sugar solutions applied to the larynx. The concentrations of these stimuli were similar to those which can be present in regurgitated stomach contents of human infants. If such regurgitated material comes in contact with laryngeal chemoreceptors, apnea, and Sudden Infant Death Syndrome (SIDS) might be elicited.