The Effect of Simulated Obstructive Apneas on Mechanical Characteristics of Lower Airways in Individuals with Asthma

Increased negative intrathoracic pressure that occurs during pharyngeal obstruction can increase thoracic fluid volume that may contribute to lower airway narrowing in individuals with obstructive sleep apnea (OSA) and asthma. Our previous study showed that fluid accumulation in the thorax induced by simulated OSA can increase total respiratory resistance. However, the effect of fluid shift on lower airway narrowing has not been investigated. To examine the effect of fluid accumulation in the thorax on the resistance of the lower airway. Non-asthma participants and individuals with (un)controlled asthma were recruited and underwent a single-day experiment. A catheter with six pressure sensors was inserted through the nose to continuously measure pressure at different sites of the airway, while a pneumotachograph was attached to a mouthpiece to record airflow. To simulate obstructive apneas, participants performed 25 Mueller maneuvers (MMs) while lying supine. Using the recordings of pressure sensor and airflow, total respiratory (R_T), lower respiratory components (R_L), and upper airway (R_UA) resistances were calculated before and after MMs. Generalized estimation equation method was used to find the predictors of R_L among variables including age, sex, body mass index, and the effect of MMs and asthma. Eighteen participants were included. Performing MMs significantly increased R_T (2.23 ± 2.08 cmH₂O/L/s, p = 0.003) and R_L (1.52 ± 2.00 cmH₂O/L/s, p = 0.023) in participants with asthma, while only R_L was increased in non-asthma group (1.96 ± 1.73 cmH₂O/L/s, p = 0.039). We found the model with age, and the effect of MMs and asthma severity generated the highest correlation (R² = 0.69, p < 0.001). We provide evidence that fluid accumulation in the thorax caused by excessive intrathoracic pressure increases R_L in both non-asthma and asthma groups. The changes in R_L were related to age, having asthma and the effect of simulated OSA. This can explain the interrelationship between OSA and asthma.