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.