Global Intelligence
The majority of studies investigating global intelligence of children with SDB report full-scale IQ scores9, 14-15 or general conceptual ability scores11,13, 16-17 in the average range compared to normative data. These findings are largely consistent among preschool,15, 18-19school-aged,14, 16, 20 and adolescent21 children across the Wechsler Abbreviated Scale of Intelligence,14, 20, 22 Wechsler Intelligence Scale for Children, Third Edition (WISC-III)16, 23 and Fourth Edition (WISC-IV)21, 24 , the Stanford Binet,18, 25 Kaufman Assessment Battery for Children,9, 26 and Wechsler Preschool and Primary Scale of Intelligence, Third Edition.15, 27 While multiple studies controlled for race11, 21, 28-29 and socioeconomic status,15, 21, 29 only one study highlighted demographic-based differences; Hunter et al11 reported that African American children had more symptoms of SDB than White American children.
Studies that implemented control groups reported that global intelligence scores are reduced in children with SDB compared to controls.5, 9, 14, 17, 19 In some studies, this effect was driven by differences in performance on non-verbal intelligence tasks17, 19 while in other studies the effect was driven by differences in verbal intelligence tasks14or unspecified differences in global cognitive function.21, 28 Therefore, while children with SDB score in the broadly average range on neuropsychological measures of intelligence, they perform lower than children in control groups. This discrepancy is partially explained by the definition of average according to the normal curve; normative data indicates that average abilities range from the 25th to the 75th percentile. Therefore, while children with SDB and children in control groups both demonstrate average intelligence according to normative data, children with SDB score on the lower end of average compared to controls.
To further explore the cognitive profiles of children with SDB, differences in global intelligence across SDB severity groups have been investigated. One study compared children with moderate SDB (AHI ≥ 5 per hour) to children with mild SDB (AHI ≤ 4 per hour) and reported lower global intelligence scores in the moderate SDB group.16 Other studies compared global intellect between children with OSA and children with PS and reported greater deficits in children with OSA.11, 28 However, findings regarding significance of SDB severity level are not consistent across all studies. A large group of studies reported no differences in global intelligence across SDB severity groups.14,15,18,21,29Three out of the five studies that reported no differences were conducted with infants and pre-school aged children.15, 29 It is possible that short-term sequelae of SDB in children this age are not severe enough to elicit impairment on objective neuropsychological measures. Therefore, differences in neurocognitive abilities may be more readily observed with prolonged exposure to intermittent hypoxia.15
To measure the impact of SDB on global intellect, multiple studies investigated associations between respiratory factors and standardized intelligence scores. Some studies that investigated associations between PSG parameters such as arousal index, obstructive apnea hypopnea index and oxygen saturation reported no associations with global intellect,5, 14, 15, 18 indicating that changes in respiratory status were not related to cognitive impairment. Other studies that measured similar PSG parameters reported that total arousal index,17 apnea hypopnea index (AHI),11 and snoring status30correlated negatively with global intelligence scores. These results suggest that higher rates of respiratory distress are related to decreased intellectual functioning in children with SDB.
In summary, research on the global intellectual profile of children with SDB is discrepant. Some of the studies reviewed above were limited by small sample sizes and a lack of a control group.16, 20 Almost all studies defined SDB severity using different criteria; some studies defined SDB severity in terms of mild, moderate, or severe OSA,14, 15, 18 while others defined SDB severity according to the presence of snoring with or without associated apneic events.5 Additional discrepancies include lack of uniformity for measures of intellectual functioning, which complicated the amalgamation of findings. In regard to referral sources, some of the studies reviewed above included participants who were referred for concerns regarding SDB,14, 15, 16, 18, 20 while others included participants recruited from the general population.5, 11, 17, 29 As noted by Smith et al30 participants referred from medical clinics likely differ from those recruited within the community. Finally, some studies did not control for covariates such as socioeconomic status (SES)11, 20 or BMI,16,20 which are known correlates of SDB. These discrepancies complicate the interpretation of the impact of SDB on global cognitive functioning.