Also, conventional scoring simply identifies discrete states, so it can overlook important variations within states, such as the distinctions between light and deep slow wave sleep, or often excludes or dilutes events through averaging. The previous application of state space techniques of sleep recordings used local field potential data, but the variability in these signals prevented comparisons between animals. Recently SST was developed to enable inter-animal comparisons of electroencephalography dynamics of sleep/wake behavior. The effect of UAO in rats on EEG dynamics of vigilance-states using SST was not explored. We hypothesized that increased respiratory efforts during UAO, in the absence of frank obstructive apneas or hypopneas, will lead to sleep/wake instability. In the present study we explored the effect of UAO on sleep state stability by using the SST at baseline and QX 222 following stimulation of sleep depth with ritanserin. We used SST to explore whether the abnormal sleep in UAO rats due to respiratory efforts reflects unstable sleep, faster Ro 15-4513 movements between states, or abnormal microarousal and transitions between states. To our knowledge this is the first study exploring the effects of UAO sleep dynamics in juvenile rats. UAO was induced in 22- day-old rats, and animals were followed for 16 days, a period that is comparable to the range of six months to eight years of age in children. This animal model��s strength and limitation was previously discussed in several studies. Briefly, the reduced respiratory rate and inspiratory swings in esophageal pressure in the current study indicate that the trachea was mildly to moderately obstructed, and these effects were not exclusively sleep related. In this model both inspiratory and expiratory loading were induced without evidence for obstructive apnea or hypopnea. This condition may resemble tracheal stenosis or upper airway resistance syndrome that are associated with large swings in intra-thoracic pressure and sleep fragmentation, even in the absence of frank apneas/hypopneas or gas exchange abnormalities. Sleep-disordered breathing is associated with intermittent upper airway obstruction at night, primarily during inspiration and is sleep related. Under these conditions animals were able to maintain ventilation and arterial PO2. It seems likely that our model also has implications for this condition since UAO animals have abnormal sleep similar to sleep-disordered breathing as seen in the subset of children with this disorder. We used the SST to explore vigilance-state dynamics in chronic UAO juvenile rats. This approach provides a novel, noncategorical method for analyzing sleep/wake behavior in chronic UAO rats.