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Review of the Role of Blood Viscosity in Obstructive Sleep Apnea and CPAP Therapy

It is known that obstructive sleep apnea syndrome (OSAS) is an independent risk factor for atherosclerosis and arterial thrombosis, both of which contribute to increased cardiovascular morbidity and mortality.  A 2013 review article published in Lung highlights the role of blood viscosity as the potential mechanism behind the increased cardiovascular risk in patients with OSAS.  Blood viscosity is the direct measure of the thickness and stickiness of blood. It determines how much friction is applied by the blood to the inner lining of vessels.

This scientific paper included a review of 5 studies positively linking blood viscosity to OSAS.  Additionally, two of these studies evaluated the effects of continuous positive airway pressure (CPAP) therapy in patients with OSAS and found that CPAP treatment reduced or normalized blood viscosity.  Proposed mechanisms for the increase of blood viscosity in patients with OSAS included changes in plasma bridging proteins, increased fibrinogen levels, increased platelet aggregation due to excessive sympathetic nervous system activity, inflammatory responses due to intermittent hypoxia, and hypoxia-induced hematopoiesis. 

Addressing the implications of blood viscosity in the development of atherosclerosis, the authors stated, “Increased viscosity may be the reason why the other biochemical, metabolic factors are important and is the underlying mechanism by which these other factors convey the preinflammatory insult to the arterial walls.”  Future studies are necessary to determine whether treatment of OSAS can stop or reverse progression of atherosclerosis and subsequent cardiovascular disease and whether reduction of blood viscosity can reduce overall cardiovascular risk. 


Toraldo DM, Peverini F, De Benedetto M, De Nuccio F. Obstructive Sleep Apnea Syndrome: Blood Viscosity, Blood Coagulation Abnormalities, and Early Atherosclerosis. Lung 2013; 191:1-7.


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