© 2003 American Thoracic Society
Obstructive Hypopneas in Children and AdolescentsNormal ValuesTo the Editor:Despite the widespread use of the apnea–hypopnea index to determine the presence of obstructive sleep apnea, there are virtually no normative data for obstructive hypopneas in children. Marcus and colleagues (1) had originally published normal values for obstructive apneas in children and adolescents in the American Review of Respiratory Diseases (now American Journal of Respiratory and Critical Care Medicine), but obstructive hypopneas were not included because no standard definition for hypopneas existed at the time. The American Academy of Sleep Medicine has subsequently published consensus definitions for scoring obstructive hypopneas in adults (2–4), which include (1) an abnormal respiratory event lasting more than 10 seconds with a 50% decrease in baseline airflow amplitude, or (2) an abnormal respiratory event lasting more than 10 seconds with a smaller reduction in airflow amplitude, but with an associated desaturation/arousal.
We therefore reviewed the original overnight polysomnographic data of 41 children (data for 9 were no longer available) from the original 50 children in the study by Marcus and colleagues (1) for obstructive hypopneas. The interested reader is referred to the original article for patient characteristics (1). Direct extrapolation of adult parameters to children may not be appropriate, because children have a faster respiratory rate and different breathing characteristics during sleep than adults (5, 6). We therefore modified the Academy of Sleep Medicine definition and defined an obstructive hypopnea as a decrease in airflow to less than 50% baseline amplitude for a minimum of two respiratory cycles. Desaturations ( Our data showed that obstructive hypopneas are uncommon in normal children. Only six children had any hypopneas. The mean duration of obstructive hypopnea was 12.8 (range 3.5–40) seconds. One child had arousals associated with hypopneas, and two children had desaturation of 3%. None of the children had carbon dioxide retention with hypopneas. The mean obstructive hypopnea index was 0.1 ± 0.1 (range 0.0–0.7) events per hour. The combined apnea/hypopnea index was 0.2 ± 0.6 (0.0–3.4) events per hour. The normative values did not vary with age. The results did not change when using the standard scoring criteria used by the American Academy of Sleep Medicine. Based on our data, the statistically significant apnea hypopnea index in healthy children is 1.5 events per hour (i.e., the mean ±2 SD). We conclude that obstructive hypopneas are uncommon in older healthy children, similar to results by Acebo and colleagues (7). Our data are limited in that they are based on older technology. New normative data are needed using newer technology, such as nasal pressure monitoring (7, 8). In the interim, these data will contribute to our understanding of what is normal. Without normative data, interpretation of obstructive hypopneas can be subjective or arbitrary, leading to inappropriate diagnosis and potentially worse morbidity.
a Childrens Hospital of Los Angeles Los Angeles, California FOOTNOTES Conflict of Interest Statement: M.B.W. has no declared conflict of interest; T.G.K. has no declared conflict of interest; S.L.D.W. has no declared conflict of interest; C.L.M. has no declared conflict of interest. REFERENCES
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3%) and arousals were scored if present, but they were not required to identify the obstructive hypopnea. 
