Correlation Found Between
Severity Of Sleep-Disordered Breathing, Size Of Tonsils, Soft Palate, And
Oropharyngeal Volume In Children
Study
is first of its kind to examine sleep-disordered breathing, pharyngeal size,
and soft tissue anatomy during childhood development
November 12, 2003
(Bethesda, MD) – Sleep-disordered
breathing (SDB) is characterized by abnormal breathing patterns during
slumber, with sleep apnea the most recognizable form. Although SBD is
commonly known to affect adults, few realize that about two percent of
children are affected. The mechanisms of SDB during development are unclear.
To test a hypothesis that a child’s anatomy –
specifically, their individual pharyngeal
geometry and/or soft tissue anatomy -- correlates with the severity
of SDB, a team of researchers has examined MRI images and other data
gathered from a group of children 7-12 years of age with sleep-related
respiratory disturbances of varying severity. The researchers found that
children with a narrow “retropalatal air space,” defined as the ratio of
the retropalatal airway cross-sectional area (CSA) to the CSA of the soft
palate, had significantly more apneas and hypopneas (abnormally slow,
shallow breathing) during sleep than did the children with relatively
unobstructed airways.
A New Study
The authors of the study, entitled “Sleep-Disordered
Breathing, Pharyngeal Size, and Soft Tissue Anatomy in Children,” are R.F.
Fregosi, S.F. Quan, K.L. Kaemingk, W.J. Morgan, J.L. Goodwin, R. Cabrera,
and A. Gmitro, all of the University of Arizona, Tucson, AZ.
Their findings appear in the online edition of November 2003 edition
of the Journal of Applied Physiology. The Journal is one of 14
journals published each month by the American Physiological Society (APS.)
Methodology
To
test their premise that pharyngeal geometry and soft tissue dimensions
correlate with the severity of sleep-disordered breathing in children, the
researchers used the following methodology:
Participants:
From an earlier study, the researchers randomly chose 10 children with a
respiratory disturbance index (RDI) of <5 and 10 children with RDI values
of >5. RDI was defined as the number of respiratory events (apneas and
hypopneas) per hour of the total sleep time, irrespective of any associated
oxygen desaturation or arousal. The final sample comprised 18 subjects, 7-12
years of age. Of this number, four snored and three of those four also had
witnessed apnea. Four other subjects had excessive daytime sleepiness, and
two of those also snored. All subjects with symptoms were placed in the
high-OAHI (obstructive apnea-hypopnea index) group.
Polysomnography:
All participants underwent unattended home polysomnography from which key
data were obtained: C3/A2 and C4/A1
electroencephalogram, right and left electrooculogram, a bipolar submental
electromyogram, thoracic and abdominal displacement, airflow, nasal
pressure, electrocardiogram, snoring, body position, pulse oximetry, and
ambient light exposure.
Airway
Imaging:
In order to be able
to study airway imaging, participants
had to be positioned within an MRI machine so that their entire pharynx was
clearly visible. Axilal images were obtained from just above the orbital
cavity to just below the larynx. Sagittal images were obtained from the
midline to the ears bilaterally. To highlight the air spaces, longitudinal
relaxation time (T1)-weighed axial and sagittal spin-echo images were
obtained in two separate series. To highlight the pharyngeal soft tissues, a
third sequence consisting of transverse relaxation time (T2)-weighted
sagittal fast spin-echo images was obtained.
Image Analysis: Because air-filled spaces are black on MRI, the
research team used a threshold method to differentiate the oropharyngeal
airway from surrounding tissue. Bony and soft tissues were analyzed using
standard radiologic landmarks. T-1--weighted axial slices were used to
measure the CSA of the tonsils at their widest point, the pharyngeal fat pad
CSA, and the intermandibular distance. Midline T-1--weighted saggital slices
were used to obtain the CSA of nasopharynx. T-2--weighted saggital images
were used to obtain the CSA of the soft palate and adenoids. Measuring the
CSA of each relevant axial slice and multiplying the CSA by the slice
thickness to obtain a volume for each slice yielded the volume of the
oropharynx. Boundaries defining the oropharynx included the tongue or soft
palate anteriorly, the pharyngeal constrictor muscle posteriorly, and the
pharyngeal tonsils laterally. A horizontal line extending from the junction
of the hard and soft palate to the posterior wall of the pharynx defined the
rostral limit of the oropharynx, while the tip of the epiglottis defined the
caudal margin.
Data Analysis: Subjects were divided into two
groups: one with high- (>7) and one with low- (<4) OAHI values.
Researchers used ANOVA, followed by the Student-Neuman-Keuls post hoc
procedure, to determine which variables were significantly different between
the groups, identifying a post hoc P value of <0.05 as
significant.
Results
Highlights of the researchers’ findings with respect
to pharyngeal geometry and soft tissue dimensions in high- and low-OAHI
groups included the following:
(1) the CSAs of the tonsils
and soft palate were significantly larger in the high- compared with the
low-OAHI group; (2) although there was a trend toward a larger adenoid
volume and pharyngeal fat pad CSA in the high-OAHI group, the differences
were not significant; and both tonsil and soft palate CSA correlated
significantly with the OAHI, accounting for 44 and 39 percent of the
variability in the OAHI, respectively; (3) significant differences between
the high- and low-OAHI groups were found for the sum of tonsil and soft
palate CSA, tonsil plus adenoid CSA, and the sum of tonsil, adenoid, and
soft palate CSA; (4) analysis of pharyngeal airway dimensions did not reveal
differences in the CSA of the retropalatal or nasopharyngeal air spaces, but
did show that the volume of the oropharynx was smaller in the high- compared
with the low-OAHI group; (5) a significant correlation between the OAHI and
the oropharyngeal volume was found; and (6) researchers found that the
narrowest diameter measured at any point in the oropharynx of children with
high-OAHI values was significantly smaller than that measured in the group
with low-OAHI values. There was also a significant correlation between this
variable and the OAHI.
With respect to the airway CSA-length relation,
researchers found:
(1) the airway was
significantly narrower in the region where the soft palate, adenoids, and
tonsils were maximally overlapped in both high- and low-OAHI groups; (2)
area-length curves of the low- and high-OAHI groups were significantly
different; and (3) subjects with narrow retropalatal air spaces tended to
have higher OAHI values.
Conclusions
From these findings, the research team has concluded
that:
-
the
severity of SBD correlates significantly with the oropharyngeal volume
and the size of the tonsils and soft palate in children 7-12 years of
age;
-
the
pharynx of children with high-OAHI values is significantly narrower
where the adenoids, tonsils, and soft palate overlap; and
-
the
OAHI is inversely and significantly related to the size of the
retropalatal air space.
Although this study has several limitations, including
the fact that a true control group composed of children with a total absence
of respiratory disturbances during sleep was not used and the researchers’
decision not to sedate the children for the imaging protocol. Nevertheless,
these findings add to the growing body of knowledge of how all children may
someday get a good night’s sleep, despite their biology.
-end-
Source:
November 2003 edition of the Journal of Applied Physiology.
The American Physiological Society (APS)
was founded in 1887 to foster basic and applied science, much of it relating
to human health. The Bethesda, MD-based Society has more than 10,000 members
and publishes 3,800 articles in its 14 peer-reviewed journals every year.
***
Editor’s Note: A copy of the research article is
available in pdf format to the press. Members of the press are invited to
obtain a pdf copy of the study and to interview members of the research
team. To do so, please contact Donna Krupa at 703.527.7357 (direct dial),
703.967.2751 (cell) or djkrupa1@aol.com.
