Subclinical sleep apnoea and plasma levels of endothelin-1 among young and healthy adults

OBJECTIVE Obstructive sleep apnoea (OSA) is a risk factor for vascular disease and other adverse outcomes. These associations may be at least partly due to early endothelin-1 (ET-1)-mediated endothelial dysfunction (ED). Therefore, we assessed the relationships between subclinical sleep apnoea and plasma levels of ET-1. METHODS We performed a population-based study among 1255 young and healthy adults aged 25-41 years. Cardiovascular disease, diabetes or a body mass index >35 kg/m2 were exclusion criteria. Plasma levels of ET-1 were measured using a high-sensitivity, single-molecule counting technology. The relationships between subclinical sleep apnoea (OSA indices: respiratory event index (REI), oxygen desaturation index (ODI), mean night-time blood oxygen saturation (SpO2)) and ET-1 levels were assessed by multivariable linear regression analysis. RESULTS Median age of the cohort was 35 years. Median ET-1 levels were 2.9 (IQR 2.4-3.6) and 2.5 pg/mL (IQR 2.1-3.0) among patients with (n=105; 8%) and without subclinical sleep apnoea (REI 5-14), respectively. After multivariable adjustment, subclinical sleep apnoea remained significantly associated with plasma levels of ET-1 (β=0.13 (95% CI 0.06 to 0.20) p=0.0002 for a REI 5-14; β=0.10 (95% CI 0.03 to 0.16) p=0.003 for an ODI≥5). Every 1% decrease in mean night-time SpO2 increased ET-1 levels by 0.1 pg/mL, an association that remained significant after multivariable adjustment (β=0.02 (95% CI 0.003 to 0.033) p=0.02). CONCLUSIONS In this study of young and healthy adults, we found that participants with subclinical sleep apnoea had elevated plasma ET-1 levels, an association that was due to night-time hypoxaemia. Our results suggest that ED may already be an important consequence of subclinical sleep apnoea.