Long term follow-up of the effect of Constant Positive Airway Pressure treatment on blood glucose control in patients with type 2 diabetes mellitus and obstructive sleep apnoea (GLYCOSA follow-up study)

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Obstructive Sleep Apnoea (OSA) affects approximately 4% (3% to 8%) of men and 2% of women in the general population, although among the obese population the prevalence is significantly higher. It is now fairly well accepted that OSA is independently associated with hypertension, and cardiovascular disease. More recently a number of studies have demonstrated an association between OSA and type 2 diabetes mellitus (T2D), insulin resistance, glucose intolerance and dyslipidemia. Indeed there is a growing body of research that suggests OSA is independently associated with insulin resistance and T2D. Furthermore, increasing insulin resistance has been correlated with increasing severity of OSA. A number of studies have examined the prevalence of OSA among people with T2D. These studies have demonstrated the prevalence of OSA could be as high as 30%, which is well above the estimated prevalence of 2–8 % in the general population. The GLYCOSA study is currently determining the direct effects of 6 months treatment with Constant Positive Airway Pressure (CPAP) on glycaemic control and other cardiometabolic factors in patients with T2D and OSA. In this study, participants with T2D were randomised into either a treatment (CPAP and lifestyle advice) group or a control (lifestyle advice only) group. Microchip downloadable S8 Autoset Spirit CPAP machines (ResMed) were used. This machine allows recording of CPAP use for at least 3 consecutive months based on time the mask is actually applied to a subject’s face (not machine run time). Data collection by the machine is not influenced by the type of mask used by the subject, provided leakage in the system is not excessively high. All subjects were counselled regarding adopting a healthy lifestyle and advised on the Heart Foundation nutrition and exercise recommendations. At the end of the 6 months, participants in the no treatment arm were offered CPAP treatment and this was done as per usual care clinical scenario. Longer term follow-up of the participants would be valuable for several reasons. First, a number of trials in diabetes in recent years have shown that the benefits of the intervention only become fully manifest with further follow-up after the trial end, despite discontinuation of the randomised allocations. Thus, benefits not apparent at trial end may be present at a later follow-up. Second, since many of the GLYCOSA participants were asymptomatic, compliance with CPAP was difficult during the randomised phase; longer term follow-up will provide an opportunity to assess compliance outside the rigours of an on-going trial. It will also allow a determination of whether any benefits seen at the 6-month trial end are sustained over a longer period. Third, CPAP was offered to participants in the control (lifestyle) arm at the end of the 6-month trial. This was done in a non-trial setting, and a comparison of compliance with, and effects of, CPAP between the two groups will provide insights into the benefits of the more intensive CPAP support provided during the trial for the CPAP group compared to the less intensive non-trial CPAP support given to the control group. The GLYCOSA has just completed all study visits and it is timely to conduct a follow-up of participants to determine the long-term impact of CPAP treatment on glycaemic control, cardiovascular outcomes and improvement in quality of life.

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