The effect of lung stretch during sleep on respiratory mechanics and variability in asthma
Campana, Lisa M.
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Both obesity and sleep are two conditions which reduce lung volume and limit deep breaths. A lack of lung stretch may alter airway smooth muscle leading to bronchoconstriction in asthma. We hypothesize that inducing dynamic changes in lung volume during sleep would reduce airway resistance in asthma. Furthermore, we hypothesized those with asthma would have increased variability of resistance during sleep as compared to healthy controls, possibly leading to nocturnal arousals. Overweight and obese subjects were studied during sleep on two nights, one baseline and one with bi-level positive airway pressure (BPAP) applied through a nasal mask. Forced oscillations were used to measure respiratory system resistance (Rrs ) and reactance (Xrs ) throughout the night and epiglottic pressure was used to separate upper airway from lower airway resistance (Rup, Rlow). Ten controls and 10 asthma subjects were studied. Rrs, Rup, and Rlow, are larger (p<0.01) and Xrs is more negative (p<0.02) in the asthma group as compared to healthy. When on BP AP, Rrs and Rup are decreased (p<0.001) and Xrs increased (p<0.01). No changes in R1ow were found with BPAP. Despite a limited effect on Rlow, high baseline Rrs was observed in the asthma group (driven primarily by the upper airway) which reduced when BP AP was applied. Mean Rrs is larger in those with astluna, but overall variability is smaller. With BP AP, both the mean and variability ofRrs decreases. Furthermore, increased variability of Rrs is found preceding arousals from sleep, particularly in those with astluna. On BPAP, variability of Rrs is greatly reduced and is no longer a predictor of arousals. We conclude that the upper airway is a large component ofRrs during sleep and that larger changes in lung volume may be required to reduce R1ow· Although BP AP does little to modulate Rlow, we found important reductions in the variability ofRrs. Those with astluna may be more likely to stay in a low resistance state when on BP AP, given the reduction in mean and variability ofRrs· Furthermore, BP AP alleviates highly variable periods of Rrs, possibly reducing the number of arousals and preventing nocturnal astluna exacerbations.
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