Investigating the Complexity of Respiratory Patterns during the Laryngeal Chemoreflex

The laryngeal chemoreflex (LCR) develops in infants as a primary sensory mechanism for defending the airway from the aspiration of liquids. Previous studies have hypothesized that prolonged apnea associated with LCR may be life threatening and might be a cause of sudden infant death syndrome (SIDS). In this study we quantify the output of the respiratory neural network, the diaphragm EMG signal, during the LCR and eupnea in early postnatal (3-10 days) piglets. We test the hypothesis that diaphragm EMG activity corresponding to reflex-related events involved in clearance (restorative) mechanisms such as cough and swallow exhibit lower complexity patterns, suggesting that a synchronized homogeneous group of neurons in the central respiratory network are active during these events. Nonlinear dynamic analysis was performed using the approximate entropy (ApEn) to asses the complexity of respiratory patterns. Diaphragm EMG (EMG_dia), genioglossal activity EMG (EMG_gg), as well as other physiological signals (tracheal pressure, blood pressure and respiratory volume) were recorded from 5 unanesthetized chronically instrumented and intact piglets. ApEn values of the EMG during cough and swallow were found significantly (p<.05 and p<0.01 respectively) lower than those of eupneic EMG.