Effect of rostral fluid shift on pharyngeal resistance in men with and without obstructive sleep apnea

Background: Obstructive sleep apnea (OSA) relates to overnight rostral fluid shift, possibly because fluid accumulation around the pharynx increases pharyngeal resistance (R-ph). 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 15 min or control, then crossed over. Leg fluid volume (LFV) and R-ph 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, R-ph increased significantly more during LBPP in the OSA group (-0.38 +/- 2.87 vs. 2.52 +/- 2.94 cmH(2)O/l/s, p = 0.016). Change in R-ph 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. (C) 2013 Elsevier B.V. All rights reserved.