Nocturnal Rostral Fluid Shift

Abstract

Background— Obstructive sleep apnea (OSA) and central sleep apnea are common in patients with heart failure. We hypothesized that in such patients, severity of OSA is related to overnight rostral leg fluid displacement and increase in neck circumference, severity of central sleep apnea is related to overnight rostral fluid displacement and to sleep P co 2 , and continuous positive airway pressure alleviates OSA in association with prevention of fluid accumulation in the neck. Methods and Results— In 57 patients with heart failure (ejection fraction ≤45%), we measured change in leg fluid volume and neck circumference before and after polysomnography, and we measured transcutaneous P co 2 during polysomnography. Patients were divided into an obstructive-dominant group (≥50% of apneas and hypopneas obstructive) and a central-dominant group (>50% of events central). Patients with OSA received continuous positive airway pressure. In obstructive-dominant patients, there were inverse relationships between overnight change in leg fluid volume and both the overnight change in neck circumference ( r =−0.780, P <0.001) and the apnea-hypopnea index ( r =−0.881, P <0.001) but not transcutaneous P co 2 . In central-dominant patients, the overnight reduction in leg fluid volume correlated inversely with the apnea-hypopnea index ( r =−0.919, P <0.001) and the overnight change in neck circumference ( r =−0.568, P =0.013) and directly with transcutaneous P co 2 ( r =0.569, P =0.009). Continuous positive airway pressure alleviated OSA in association with prevention of the overnight increase in neck circumference ( P <0.001). Conclusions— Our findings suggest that nocturnal rostral fluid shift is a unifying concept contributing to the pathogenesis of both OSA and central sleep apnea in patients with heart failure.