The effect of lung stretch during sleep on airway mechanics in overweight and obese asthma

Both obesity and sleep reduce lung volume and limit deep breaths, possibly contributing to asthma. We hypothesize that increasing lung volume dynamically during sleep would reduce airway resistance in asthma. Asthma (n = 10) and control (n = 10) subjects were studied during sleep at baseline and with increased lung volume via bi-level positive airway pressure (BPAP). Using forced oscillations, respiratory system resistance (Rrs) and reactance (Xrs) were measured during sleep and Rrs was partitioned to upper and lower airway resistance (Rup, Rlow) using an epiglottic pressure catheter. Rrs and Rup increased with sleep (p < 0.01) and Xrs was decreased in REM (p = 0.02) as compared to wake. Rrs, Rup, and Rlow, were larger (p < 0.01) and Xrs was decreased (p < 0.02) in asthma. On BPAP, Rrs and Rup were decreased (p < 0.001) and Xrs increased (p < 0.01), but Rlow was unchanged. High Rup was observed in asthma, which reduced with BPAP. We conclude that the upper airway is a major component of Rrs and larger lung volume changes may be required to alter Rlow.

► Sleep and obesity cause reductions in lung volume, contributing to asthma.
► Increases in lung volume during sleep may reduce airway resistance.
► Resistance was quantified during sleep on and off positive airway pressure (PAP).
► Upper airway resistance was reduced with Bi-level PAP.
► Upper airway resistance is a large component of total resistance, particularly in asthma.