There were 3 major findings in our study of TNI. First, in a group of predominantly obese children with and without adenotonsillectomy, TNI treated sleep apnea across a wide spectrum of disease severity. Second, in the majority of children, the reduction in the AHI with TNI was comparable to CPAP. Third, during NREM sleep, all of the children had prolonged periods of inspiratory flow limitation that were associated with an increase drespiratory rate and inspiratory duty cycle, all of which decreased with TNI. Our data suggest that TNI may offer an alternative to CPAP in some children for whom standard treatment approaches are not successful.
Previously, we demonstrated that TNI treated all of the adult participants with mild sleep apnea and approximately half of the adult participants with moderate and severe sleep apnea.19
Children in the current study were equally distributed across a spectrum of disease severity (mild AHI: >2 and ≤5 events per hour, n
= 4; moderate AHI: >5 and ≤10 events per hour, n
= 4; and severe AHI: >10 events per hour, n
= 4). TNI reduced the AHI during both NREM and REM sleep, but this effect depended on the disease severity. In the 8 children with mild-to-moderate sleep apnea, TNI decreased the AHI consistently, with a mean reduction from 6 ± 3 to 2 ± 1 events per hour. In contrast, in the 4 children with severe sleep apnea, TNI had an inconsistent response: in 1 child, the AHI was unchanged, in 2 children the AHI decreased by 72% and 36% but the effect was suboptimal, and the fourth child had a marked reduction in the AHI from 17 to 2 events per hour. The 3 children whose AHI remained above 10 events per hour () were unique in the following aspects: they were all girls, markedly obese, and were in Tanner stage 2 to 3 as compared with the other children, who were generally younger and in Tanner stage 1. Thus, TNI might offer a treatment option for children with mild-to-moderate OSA and in selected children with severe OSA.
OSA is the result of increased upper airway collapsibility during sleep, as reflected in the critical closing pressure.2,3,30–33
Previously, we demonstrated that TNI primarily acts by slightly increasing pharyngeal pressure19
that was particularly effective in adults with minimal increases in critical closing pressure manifested clinically by snoring and hypopneas.34
Similarly, TNI alleviated inspiratory flow limitation during NREM sleep (). The marked reduction in apneic events during REM sleep, however, was greater than anticipated. This finding suggests that TNI might have increased pharyngeal pressure more in children than adults because of the relatively larger size of the nasal cannula compared with the size of the nares. Alternatively, the slight increase in pharyngeal pressure might have increased lung volume to a greater degree in children resulting from higher chest wall and lung compliance,35
particularly during REM sleep, when the chest wall musculature is hypotonic.36
Increases in lung volume might have improved both oxygen stores and upper airway patency.37–40
Finally, it is also possible that insufflation of air might have stimulated upper airway neuromuscular responses, thereby improving upper airway patency.41
Regardless, the improvements in flow limitation, respiratory rate, and inspiratory duty cycle suggest that TNI increased inspiratory tidal volumes through increased inspiratory airflow. Moreover, the improvement in the AHI with TNI suggests that the increases in inspiratory airflow and tidal volumes were sufficient to prevent hypoxia or arousals, which has significant implications for the management of sleep-disordered breathing in children.
There are several advantages of TNI. First, the patient interface is a nasal cannula that is less cumbersome than a nasal mask and should be better tolerated by children during sleep. All of the participants readily agreed to sleep with a TNI device, and only 2 participants described mild discomfort once the TNI device began to deliver air. One complaint was temperature related and was easily adjusted to the participant’s preference; 1 participant intermittently removed the cannula during the course of the night but was unable to effectively verbalize her complaint. Second, TNI delivers heated and humidified air at the level of the nares, which avoids nasal dryness and irritation. Third, for the majority of children, the response to TNI was comparable to CPAP. Taken together, if improved comfort with TNI leads to increased adherence to treatment, TNI might ultimately be a more effective treatment option than CPAP, even in children with suboptimal responses. To assess this hypothesis, however, adherence with TNI needs to be assessed in the home setting. Fourth, the use of CPAP in children carries concern for the potential of compression of boney facial structures. TNI is an open system that is not dependent on a tightly sealed nasal mask obviating concerns of facial compression.
There were several limitations in our study. First, carbon dioxide levels were evaluated during the baseline study, but the high airflow rate of TNI eliminated the end-tidal CO2 measurement during the treatment night. The loss of a consistent CO2 measurement limited our ability to assess the effect of TNI on ventilation during the treatment night. Second, the sample size was limited, and the effect of TNI on severe sleep apnea is not completely understood. The spectrum of patients with regard to disease severity and previous adenotonsillectomy, however, was diverse and likely representative of patients who would require treatment for sleep apnea. Third, the total sleep times during both nights were limited because of testing conditions, which included an early awakening time. Additional evaluation of the effect of TNI on sleep time, sleep latency, and sleep architecture should be assessed in future studies. Fourth, the assessment of respiratory pattern changes during NREM sleep with TNI was measured with a random sample of breaths. It is possible that the changes observed in the respiratory pattern on TNI might have been more accurately characterized if the assessment was expanded to include all breaths during NREM sleep.