Abstract
Sleep apnea (SA), a condition associated with increased cardiovascular risk, has been traditionally associated with obesity and aging. However, in patients with fluid-retaining states, such as congestive heart failure and end-stage renal disease, both prevalence and severity of SA are increased. Recently, fluid shift has been recognized to play an important role in the pathophysiology of SA, since the fluid retained in the legs during the day shifts rostrally while recumbent, leading to edema of upper airways. Such simple physics, observed even in healthy individuals, has great impact in patients with fluid overload. Correction of the excess fluid volume has risen as a potential target therapy to improve SA, by attenuation of nocturnal fluid shift. Such strategy has gained special attention, since the standard treatment for SA, the positive airway pressure, has low compliance rates among its users and has failed to reduce cardiovascular outcomes. This review focuses on the pathophysiology of edema and fluid shift, and summarizes the most relevant findings of studies that investigated the impact of treating volume overload on SA. We aim to expand horizons in the treatment of SA by calling attention to a potentially reversible condition, which is commonly underestimated in clinical practice.
Highlights
Sleep apnea (SA) is a condition characterized by repeated episodes of complete or partial airflow cessation during sleep, typically referred as apnea and hypopnea
Transpharyngeal trousers for 15 min resistance and PCO2 increased in patients with obstructive sleep apnea (OSA), while the opposite occured in central sleep apnea (CSA)-dominant patients
The proof of concept that fluid overload can impact in the severity of OSA in patient on dialysis was demonstrated by Lyons and coworkers, who showed that apnea–hypopnea index (AHI) fell by 36% after removal of an average of 2.2 L by ultrafiltration alone in end-stage renal disease (ESRD) patients [62]
Summary
Sleep apnea (SA) is a condition characterized by repeated episodes of complete or partial airflow cessation during sleep, typically referred as apnea and hypopnea. The apnea–hypopnea index (AHI), defined as the total number of episodes of apnea and hypopnea per hour of sleep, is routinely used to diagnose SA and to classify it as mild (AHI between 5 and 15), Abbreviations: AHI, apnea–hypopnea index; CHF, congestive heart failure; CKD, chronic kidney disease; CPAP, continuous positive airway pressure; CSA, central sleep apnea; EABV, effective arterial blood volume; ESRD, end-stage renal disease; LBPP, lower body positive pressure; OSA, obstructive sleep apnea; PCWP, pulmonary capillary wedge pressure; SA, sleep apnea. The prevalence of SA increases over time, since obesity, one of the most important risk factors, has increased in general population. More recent data suggest that more than 20% of adults have mild SA and up to 7% have moderate or severe SA [11]
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