Effect of Weight Loss and CPAP on OSA and Metabolic Profile Stratified by Craniofacial Phenotype

Obstructive sleep apnea (OSA) is a common form of sleep-disordered breathing (SDB). It causes sleep fragmentation, disabling daytime sleepiness, impaired cognitive function, poor quality of life and cardiovascular diseases. Weight reduction has always been advocated in patients with OSA who are overweight and may lead to improvement in the severity of OSA. Previous study reported a randomized controlled trial of dietician-led lifestyle modification program (LMP) in 104 patients and found that LMP group had significantly more weight loss and reduced OSA severity, and the response was sustained after 8 months. However, a wide variety of response to the therapy was observed with 21.3% of patients with severe disease that converted to mild to moderate and only 6.6% of those with severe disease who became mild in severity. Apart from obesity, craniofacial factors are well recognized in the pathogenesis of OSA and are likely to play an important role in influencing the response to weight loss. For the same degree of OSA severity, Caucasians were more overweight whereas Chinese exhibited more craniofacial bony restriction. Recent studies showed that a smaller craniofacial skeleton is associated with better response from weight loss program in terms of OSA improvement. With vast majority of studies investigating the cardiometabolic changes after CPAP or weight loss on patients with OSA, evaluation based on craniofacial restriction, the key factor in the pathogenesis, is lacking.

This study aimed to compare the effect of weight loss or CPAP alone on subclinical inflammation, insulin resistance and blood pressure in patients with obesity and moderate-to-severe obstructive sleep apnea, stratified according to the degree of craniofacial restriction.

The study plans to recruit consecutive patients who have been referred to the Respiratory Clinic at the Prince of Wales Hospital with clinical suspicion of sleep-disordered breathing with specific study entry criteria including an age of 18 or more, body mass index (BMI) >25 kg/m2, and moderate to severe OSA diagnosed by home sleep study. Patients having conditions that will affect the serum level of hsCRP will be excluded.

Inclusion criteria

• Patients diagnosed with moderate or severe obstructive sleep apnea ( apnea hypopnea index (AHI) ≥ 15); body mass index ≥25 kg/m2; age 18-70 years.

Exclusion criteria

• Predominant central sleep apnea; conditions that will affect the level of hsCRP; unstable cardiovascular disease (e.g. recent unstable angina, myocardial infarction, stroke or transient ischemic attack within the previous 6 months or severe left ventricular failure; neuromuscular disease affecting or potentially affecting respiratory muscles; moderate to severe respiratory disease (i.e. breathlessness affecting activities of daily living) or documented hypoxemia or awake SaO2 <92%); psychiatric disease that limits the ability to give informed consent or complete the study.