Video and polysomnography
All children underwent overnight PSG in a sleep unit. Heart rate,
electrocardiographic signals, electroencephalographic (EEG) and
electrooculographic activities, thoracic and abdominal respiratory
movements, respiratory rate, arterial oxygen saturation (SaO2) and
airflow were continuously measured throughout the sleep period. Along
with the PSG recording, a video was recorded with a Sony® Ipela
SNC-ER550 rotating camera coupled to an infrared device to allow
recording in low light conditions without disturbing the child’s sleep.
The video was synchronized to PSG. The camera was placed on the wall
opposite the child’s bed, at 2.5 meters and positioned to focus on the
child’s head and chest. Sheets and blankets were avoided as often as
possible, and if needed for the child to fall asleep, removed as soon as
he slept. A sound recording, assessed in decibels, was also made at the
same time.
Interpretation of the PSG data, blinded to the clinical examination and
SHS, was carried out according to the AASM criteria of the AASM
[12,
13]. Patients were classified in four
OSAHS severity groups: absence (OAHI < 1.5 per hour), mild
(OAHI 1.5-5), moderate (OAHI 5-10) and severe (OAHI ≥ 10). The ODI was
calculated as the number of decreases in SaO2 ≥ 3%
[20].
The PSG videos were evaluated throughout the second sleep cycle
identified by EEG signals as the period between the end of the first
rapid eye movement (REM) sleep and the end of the second one. The
analysis was blinded to OAHI, ODI and SHS values. The videos were
interpreted by an otorhinolaryngologist investigator according to a
slightly modified version of Sivan’s scoring system. The following
parameters were considered: presence of inspiratory noise, type of
inspiratory noise, movements during sleep, number of waking episodes,
number of apneas, chest retractions, and mouth breathing (Table 1). The
movements of more than four body parts (four limbs, head, and chest)
were considered as a whole-body movement. Any opening of the eyes or a
shift to a sitting position were counted as a waking episode. All events
characterized by breathing interruption with persistent respiratory
effort for more than two respiratory cycles were counted as apneas.
Diaphragmatic paradoxical movements were analyzed together with the
chest retractions. For the third item (movements during sleep), we set
the threshold for numerous movements at 2 rather than 3 in Sivan’s
original scoring system. Likewise, for the fifth item (number of
apneas), we set the threshold of numerous apneas at 2 rather than 3.
The score obtained for the second sleep cycle of each child was then
brought back first to a 30-minute duration, leading to a 30-minute risk
score (RS30), then to a 10-minute duration, leading to a 10-minute risk
score (RS10). The number of apneas, waking episodes and movements was
averaged for a 30-minute period using the following formula: (number of
apneas + number of waking episodes + number of movements) over 30
minutes = (number of apneas + number of waking episodes + number of
movements) over the entire second sleep cycle*30/ length of the second
sleep cycle in minutes. The same calculations were performed for a
10-minute period. For the other variables (inspiratory noise,
intercostal retractions, mouth respiration), only their intermittent or
continuous nature was noted, hence their value was unchanged
irrespective of the duration.