Complexity measures of the central respiratory networks during wakefulness and sleep in piglets

In this study, we examine EMGdi complexity before and after general (muscimol) inhibition of respiratory neurons within the rostral ventral medulla (RVM). We inserted a microdialysis guide tube into the RVM region, allowing us to dialyze muscimol on a daily basis during experiments. Animals were studied using the technique of barometric plethysmography, allowing us to measure ventilation without restraint. The EMGdi signals were recorded from 5 unanesthetized, chronically instrumented and intact piglets (3-10 days old) during eupnea before and after general inhibition of respiratory neurons in the RVM and analyzed using the approximate entropy and fractal analysis methods. Ten consecutive breaths were taken after 6 continuous minutes of unequivocal wakefulness, 3 minutes of NREM and 1 minute of REM sleep. Once the control responses to room air were measured, we dialyzed muscimol. GABA_A agonist (10mM) into the RVM and repeated in room air. Note that muscimol is an nonspecific inhibitor and inhibits the neurons in the RVM. The EMGdi signals were recorded from 4 unanesthetized, chronically instrumented piglets (3-10 days old) during eupnea and analyzed using the expectation-maximization (EM) fractal method as in the first set of experiments, The complexity values in NREM were reduced more by the inhibition than were the awake stage. However, the changes in the complexity values due to the inhibition of the RVM were much more prominent during REM. The differences in the complexity measures of EMGdi before and after muscimol dialysis were statistically significant (p<0.01) during REM and NREM, but not during wakefulness. Our findings show that inhibition of the RVM reduced the complexity of the respiratory patterns significantly (p<0.05) during NREM and REM sleep stages. These data indicate that the RVM plays an important role in both the control of sleep and the sudden infant death syndrome (SIDs).