Comment accompanying: obstructive sleep apnoea: a stand-alone risk factor for chronic kidney disease by Chou Yu-Ting

Sleep apnoea (SA) is a high priority health problem because it disrupts sleep and reduces quality of life, it is associated with obesity, hypertension, especially resistant hypertension, congestive heart failure, diabetes and it engenders cardiovascular (CV) complications and death. The following types of apnoea can be distinguished: (i) obstructive, (ii) central (i.e. neurally mediated) and (iii) mixed. Obstructive SA (OSA) is characterized by a cessation of airflow caused by occlusion of the oropharyngeal tract and central SA by a transient abolition of the neural drive to respiratory muscles. Mixed apnoea represents a combination of the two forms. SA is one of the most important triggers of high sympathetic activity and it is perhaps the most important non-traditional risk factor underlying the high CV risk of chronic kidney disease (CKD). The high sympathetic activity engenders three intermediate mechanisms, chronic hypertension, left ventricular hypertrophy and arrhythmias, particularly atrial fibrillation, which eventually leads to CV complications and death. SA is common in end-stage renal disease and studies in haemodialysis and peritoneal dialysis patients coherently show that intensive dialysis improves SA in patients with severe sleep disordered breathing. Renal transplantation is in theory the ideal way of correcting SA, because a restored renal function abrogates the uraemic toxicity. In a case-control study, the prevalence of mild and severe SA was almost identical in renal transplant patients as compared to age-, sex- and body mass index-matched healthy subjects, supporting the contention that renal transplantation reverses SA. A study published in this issue of Nephrology, Dialysis Transplantation assesses the association between CKD and SA in symptomatic (snorers) patients, excluding by protocol those with hypertension and diabetes, which are well-known risk factors for SA and CKD. The primary hypothesis tested in this study, i.e. whether snorers are at a higher risk for renal dysfunction, is a sensible one.