The Effect of Body Position on Esophageal Reflexes in Cats: A Possible Mechanism of SIDS?

BACKGROUND: It has been hypothesized that life threatening events are caused by supra-esophageal reflux (SER) of gastric contents which activates laryngeal chemoreflex-stimulated apnea. Placing infants supine decreases the risk of sudden infant death syndrome (SIDS). The aim of this study was to determine whether body position affects esophageal reflexes that control SER. METHODS: We instrumented the pharyngeal and esophageal muscles of decerebrate cats (N=14) to record EMG or manometry, and investigated the effects of body position on the esophago-upper esophageal sphincter (UES) contractile reflex (EUCR), esophago-UES relaxation reflex (EURR), esophagus-stimulated pharyngeal swallow response (EPSR), secondary peristalsis (SP), and pharyngeal swallow (PS). EPSR, EUCR, and SP were activated by balloon distension, EURR by air pulse, and PS by nasopharyngeal water injection. The esophagus was stimulated in the cervical, proximal thoracic, and distal thoracic regions. The threshold stimulus for activation of EUCR, EURR and PS, and the chance of activation of EPSR and SP were quantified. RESULTS: We found that only EPSR was significantly more sensitive in the supine vs prone position regardless of the stimulus or the position of the stimulus in the esophagus. CONCLUSION: We hypothesize that the EPSR may contribute to the protection of infants from SIDS by placement in the supine position.