Background: Obstructive sleep apnea (OSA) relates to overnight rostral fluid shift, possibly because fluid accumulation around the pharynx increases pharyngeal resistance (Rph). We hypothesised that Rph will increase more in men with than without OSA in response to rostral fluid redistribution.
Methods: Seventeen men with, and 12 without OSA were randomized to lower body positive pressure (LBPP) for 15min or control, then crossed over. Leg fluid volume (LFV) and Rph were measured before and after each period.
Results: LBPP displaced similar amounts of fluid from the legs in both groups. However, compared to the non-OSA group, Rph increased significantly more during LBPP in the OSA group (-0.38±2.87 vs. 2.52±2.94cmH2O/l/s, p=0.016). Change in Rph during LBPP correlated directly with baseline Rph in the OSA group, but inversely in the non-OSA group.
Conclusion: OSA patients have increased susceptibility to pharyngeal obstruction in response to rostral fluid redistribution, which could predispose to pharyngeal collapse during sleep.
Keywords: Obstructive sleep apnea; Rostral fluid shift; Upper airway.
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