Selective effects of CPAP on sleep apnoea-associated manifestations

Visceral adiposity and obstructive sleep apnoea (OSA) may be independently associated with daytime sleepiness/low performance, insulin resistance, hypercytokinaemia, and/or hypertension. The objectives of this study are to simultaneously test these associations at baseline and after 3 months of continuous positive airway pressure (CPAP) therapy.

Sixteen obese men with OSA; 13 non-apnoeic, obese controls, and 15 non-obese controls were monitored in the sleep laboratory for four consecutive nights. Objective measures of daytime sleepiness and performance, serial 24 h plasma measures of interleukin-6 (IL-6), tumour necrosis factor-alpha (TNF-alpha), TNF receptor 1 (TNF-r1) and adiponectin, fasting blood glucose and insulin, visceral adiposity and blood pressure were obtained. Sleep apnoeics were re-assessed using the same protocol after 3 months of CPAP.

At baseline, IL-6, TNF-r1, and insulin resistance were highest in OSA patients, intermediate in obese controls, and lowest in non-obese controls (P < 0.05). Visceral fat was significantly greater in sleep apnoeics than obese controls and predicted insulin resistance and IL-6 levels, whereas OSA predicted TNF-r1 levels (P < 0.05). CPAP decreased daytime sleepiness and blood pressure (P < 0.05), but did not affect fasting glucose or insulin or around the clock adiponectin, IL-6, TNF-alpha, or TNF-r1 levels.

In obese sleep apnoeics, visceral fat is strongly associated with insulin resistance and inflammation. CPAP decreases sleepiness and moderates hypertension but does not affect visceral adiposity, insulin resistance, hypoadiponectinaemia or hypercytokinaemia, all of which are independent risk factors for cardiovascular disease and diabetes.