Introduction Sleep-disordered Breathing (sdb) Is a Frequent Con- Dition That Affects Both Children and Adults1-4 and Is Associated with Disruption of Alveolar Ventila-

SLEEP-DISORDERED BREATHING (SDB) IS A FREQUENT CONDITION THAT AFFECTS BOTH CHILDREN AND ADULTS1-4 AND IS ASSOCIATED WITH DISRUPTION OF ALVEOLAR VENTILATION, HYPOXEMIA, AND SLEEP FRAGMENTATION. Sleep fragmentation in healthy adults, ie, the presence of multiple respiratoryrelated arousals during sleep, correlates with neurobehavioral performance decrements the following day.5-7 In contrast, despite the presence of substantial neurocognitive morbidity,8-11 it is assumed that sleep architecture is preserved in children with SDB,12-14 possibly because criteria for arousal are based on those defined for adults.15 However, changes in spectral power have been observed during obstructive events in children without obvious electroencephalogram (EEG) arousal,16 suggesting that current techniques for assessment of arousal may not be sensitive enough in children, and therefore fail to detect sleep fragmentation in the pediatric population.16 Arousals during sleep are associated with increases in sympathetic activity in normal adults.17 Therefore, measurement of sympatheticactivity changes using noninvasive approaches, eg, heart-rate variability18 or pulse transit time,19-20 may provide a practical method for arousal detection. A recently developed technique allowing for noninvasive moment-to-moment measurement of sympathetic tone is peripheral arterial tonometry (PAT). PAT employs finger plethysmography such that changes in sympathetic activity, which elicit robust changes in peripheral vascular cutaneous perfusion, are detected on a beat-to-beat basis. In adults, PAT-signal attenuations with concomitant changes in heart rate correlate with respiratory disturbances,21-22 as well as with EEG arousals.23 Thus, we hypothesized that PAT monitoring may provide a sensitive measure of arousals in children.