Effects of Reflux Laryngitis on Laryngeal Chemoreflexes in Newborn Lambs

Short title: Reflux laryngitis and laryngeal chemoreflexes ABSTRACT It has been suggested that reflux laryngitis (RL) is involved in apneas-bradycardias of the newborn. The aim of the present study was to develop a unique RL model in newborn lambs in order to test the hypothesis that RL enhances the cardiorespiratory components of the laryngeal chemoreflexes (LCR) in the neonatal period. Gastric juice surrogate (2 mL HCl + pepsin, pH 2) (RL group, n = 6) or saline (Control group, n = 6) was repeatedly injected onto the posterior aspect of the larynx, 3 times a day for 6 consecutive days, via a retrograde catheter introduced into the cervical esophagus. Lambs instilled with gastric juice surrogate presented clinical signs of RL, as well as moderate laryngitis on histological observation. Laryngeal chemoreflexes were thereafter induced during sleep by injection of 0.5ml of HCl (pH 2), milk, distilled water or saline into the laryngeal vestibule via a chronic, transcutaneous supra-glottal catheter. Overall, RL led to a significantly greater respiratory inhibition compared to the Control group during LCR, including longer apnea duration (p = 0.01), lower minimal respiratory rate (p = 0.002) and a more prominent decrease in SpO2 (p = 0.03). No effects were observed on cardiac variables. In conclusion, 1) our unique neonatal ovine model presents clinical and histological characteristics of RL; 2) the presence of RL in newborn lambs increases the respiratory inhibition observed with LCR, at times leading to severe apneas and desaturations.