Cardiovascular Consequences of Sleep Apnea

Henry K. Yaggi, MD

Department of Internal Medicine
Pulmonary and Critical Care Medicine
New Haven, Connecticut

Studies have shown that 60% to 70% of patients with a history of stroke also have obstructive sleep apnea (OSA), but the relationship is uncertain.[1, 2] Important questions persist: Does a history of stroke predispose patients to a high rate of OSA, does OSA increase the risk of stroke, or both? There are often confounding variables associated with OSA and stroke, such as obesity, high blood pressure, diabetes, and hyperlipidemia. These comorbidities are present in many individuals with OSA or stroke, and make the direct relationship between OSA and stroke difficult to comprehend. Certainly, studies have demonstrated an association between stroke and OSA. For example, one seminal study of 167 men demonstrated that 36% had a stroke while sleeping; snoring was the only significant risk factor associated with stroke.[3] Since then, more sophisticated studies found a significant association between the number of apnea and hypopnea episodes patients have per hour (measure of OSA severity) and the incidence of stroke.[1, 2, 4, 5] The cause and effect relationship is a highly investigated topic. Some studies have attempted to establish a direct cause and effect relationship by demonstrating the connection of stroke and OSA to the pathophysiologic pathway. Animal and human studies have long demonstrated that stroke-induced brain lesions can affect centers necessary for normal breathing and cause OSA.[6-9] Studies also show that treatment of OSA reduces the incidence of stroke. Stroke patients with OSA treated with continuous positive airway pressure (CPAP) have significantly fewer vascular events compared to OSA patients not treated with CPAP. [10-12] Taken together, these and other studies have demonstrated a significantly greater risk of stroke in OSA patients compared to controls.[13-15] Although only partly understood, researchers hypothesize that OSA-induced hypoxemia and elevated autonomic arousals might have short- and long-term effects on cardiac rhythm, blood pressure, intracranial pressure, and blood flow that could predispose patients to stroke.[2, 16] The apparent reciprocal relationship between stroke and OSA warrants special attention in patients with stroke, OSA, or both.

References

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