APNEA: DOES LARYNGEAL MICROASPIRATION PLAY A ROLE?

Abstract

To examine physiologic mechanisms whereby gastroesophageal reflux might cause apnea, we examined the breathing pattern and airway response after intralaryngeal infusion of 0.1 and 0.5cc each of saline, cow's milk formula, and 0.1N HC1 in 9 adult cats. Anesthetized animals breathed spontaneously through a tracheostomy tube. A second tracheal cannula directed rostrally allowed direct stimulation of the larynx from below. Pulmonary function was determined from simultaneous measurements of intrathoracic pressure by intrapleural catheter, air flow by pneumotachograph, and lung volume by flow integration. Results: 1) None of the stimuli was followed by apnea defined as cessation of effective tidal volume × 15sec. 2) A cough response was elicited in 6 of 9 animals following 0.1N HCl only. 3) A short latent, rapidly adapting (20sec) decrease in respiratory rate from control (25.9±4.9 br/min) was noted following milk (19.4±3.7 br/min) and acid (13.5±1.2 br/min) infusion (p < .01) despite continued presence of stimuli in the larynx at both volumes tested. 4) 0.1N HCl alone produced a short latent, rapidly adapting (20sec) increase in total lung resistance (47.6 ±10.6 cm H2O/L/sec vs control of 23.3±1.7, p < .01). 5) Pretreatment of laryngeal mucosa with Benzocaine abolished the response to all stimuli. CONCLUSIONS: 1) Apnea is not the major response following laryngeal aspiration. 2) Aspiration of microvolumes of acid produces a more significant pulmonary response than milk aspiration. 3) Responses to both stimuli are mediated by rapidly adapting mucosal receptors. 4) Thus, in infants with apnea, combined respiratory and intraesophageal monitoring should include recording of respiratory rate and cough.