Influence of Craniofacial Restriction on Rebound of Obstructive Sleep Apnea Following Weight Gain
Influence of Craniofacial Restriction on Rebound of Obstructive Sleep Apnea Following Weight Gain
Apart from obesity, craniofacial factors are well recognized in the pathogenesis of
 obstructive sleep apnea (OSA) and are likely to play an important role in influencing the
 response to weight loss. The prevalence of OSA syndrome is as common among the middle-aged
 Hong Kong Chinese populations as the Caucasians, despite our Chinese patients having much
 lower body mass index (BMI). From previous work on ethnic comparison, for the same degree of
 OSA severity, Caucasians were more overweight, whereas Chinese exhibited more craniofacial
 bony restriction. Cephalometric measurements based on lateral radiograph of the upper airway
 have shown that a shorter distance between maxillary projection from the cranial base, a
 smaller posterior airway space, less mandibular protrusion, a narrower space between the hard
 palate and cranial base, and a more caudally placed hyoid bone predispose to a higher
 apnea-hypopnea index (AHI). A recent study shown that a shorter mandibular length as measured
 by lateral cephalometry was associated with a greater fall in AHI after weight loss. Another
 study using craniofacial computed tomography (CT) scans to evaluate the maxillomandibular
 bony volume found that craniofacial restriction influenced the relationship between weight
 loss and OSA improvement. Collectively, these studies suggest that the effect on AHI with
 weight loss is likely to be more pronounced in those with a smaller craniofacial skeleton.
 However, the effect of the craniofacial restriction on the degree of rebound in OSA following
 weight gain after the weight loss intervention is unknown.

 The study aims to investigate the change in weight and OSA severity following cessation of a
 lifestyle modification program (LMP) and examine the relationship between craniofacial
 restriction and the degree of OSA reoccurrence.
All subjects will be advised to stop using continuous positive airway pressure (CPAP) for at
 least 7 days as previous study showed that severity of obstructive sleep apnea (OSA) did not
 increase further after the first week of CPAP withdrawal. Subjects will then be invited to
 undergo a limited sleep study using "EMBLETTA" portable diagnostic system (MEDCARE, Iceland).
 The EMBLETTA is a pocket-sized digital recording device. It is a multi-channel transducer,
 providing an apnea-hypopnea index (AHI) based on recording time. It also detects both
 respiratory and abdominal efforts through the effort sensor and can differentiate between
 obstructive and central events. Built-in position sensors are also available to differentiate
 supine from non-supine events. Respiratory events are scored when desaturations of at least
 4% occurred in the absence of moving artefacts and irrespective of co-existing changes in
 snoring or heart rate. The EMBLETTA operates on battery power, with the internal memory
 storage of 16 MB, which allows approximately 12 hours of data collection. The EMBLETTA
 default settings for apneas and hypopneas will be used in this study. An apnea is defined as
 a decrease in airflow by 80% of baseline for at least 10 seconds. The EMBLETTA default
 maximum apnea duration is set at 80 seconds. A hypopnea is defined as a decrease in airflow
 by 50% of baseline for at least 10 seconds. The EMBLETTA default maximum hypopnea duration is
 set at 100 seconds. The EMBLETTA AHI used for analysis is automatically analysed by the
 EMBLETTA software. The EMBLETTA device has been validated against hospital-based
 polysomnography in the Hong Kong Chinese population. The EMBLETTA is a highly sensitive and
 specific screening device in quantifying AHI and differentiating obstructing and supine
 events when compared against polysomnography (PSG) in patients with suspected OSA. Patients
 will be instructed how to operate the EMBLETTA device for the sleep recording and estimate
 their time of sleep. Those who have failed the EMBLETTA sleep study will be arranged to have
 a second home EMBLETTA sleep study. Patients who are symptomatic of OSA with a negative home
 EMBLETTA sleep study will be arranged to have a hospital-based PSG.

 All subjects will undergo three-dimensional (3D) computed tomography (CT) scans of the
 head/neck region to evaluate the upper airway and craniofacial structures. Craniofacial
 restriction is determined by measuring the size of the maxillomandibular volume based on the
 mandibular cephalometric landmarks (left and right condylion, left and right gonion, anterior
 nasal spine (ANS) and menton) as per previous published study. The patient is positioned in
 the natural head position with a closed lip and bite. All measurements will be made by a
 single assessor and the analysis will be performed blind to knowledge of weight loss and AHI
 data.

 All subjects will go through several measurements. These include assessment of subjective
 sleepiness with the Epworth Sleepiness scale (ESS), anthropometric measurements (body mass
 index, neck and waist circumference) and blood pressure.

 The ESS is a questionnaire specific to symptoms of daytime sleepiness and the patients are
 asked to score the likelihood of falling asleep in eight different situations with different
 levels of stimulation, adding up to a total score of 0 to 24.
Inclusion Criteria:

 -  Subjects are participants in a previously described dietician-based weight loss study
 in obese Chinese with obstructive sleep apnea (OSA). Specific study entry criteria
 included an age range between 30 and 80 years, body mass index (BMI) >25 kg/m2, and
 moderate to severe OSA (apnea-hypopnea index (AHI) >15 events/hour) before the weight
 loss program performed in the year of 2010-2013.

 Exclusion Criteria:

 -  Subjects refused to participate the trial or unable to consent.