title: Effects of Altered Intra-abdominal Pressure on the Upper Airway Collapsibility in a Porcine Model.
abstract: BACKGROUND
  Obstructive sleep apnea is strongly associated with obesity, particularly abdominal obesity common in centrally obese males. Previous studies have demonstrated that intra-abdominal pressure (IAP) is increased in morbid obesity, and tracheal traction forces may influence pharyngeal airway collapsibility. This study aimed to investigate that whether IAP plays a role in the mechanism of upper airway (UA) collapsibility via IAP-related caudal tracheal traction.
  
  
  METHODS
  An abdominal wall lifting (AWL) system and graded CO2pneumoperitoneum pressure was applied to four supine, anesthetized Guizhou miniature pigs and its effects on tracheal displacement (TD) and airflow dynamics of UA were studied. Individual run data in 3 min obtained before and after AWL and obtained before and after graded pneumoperitoneum pressure were analyzed. Differences between baseline and AWL/graded pneumoperitoneum pressure data of each pig were examined using a Student's t-test or analysis of variance.
  
  
  RESULTS
  Application of AWL resulted in decreased IAP and significant caudal TD. The average displacement amplitude was 0.44 mm (P < 0.001). There were three subjects showed increased tidal volume (TV) (P < 0.01) and peak inspiratory airflow (P < 0.01); however, the change of flow limitation inspiratory UA resistance (Rua) was not significant. Experimental increased IAP by pneumoperitoneum resulted in significant cranial TD. The average displacement amplitude was 1.07 mm (P < 0.001) when IAP was 25 cmH2O compared to baseline. There were three subjects showed reduced Rua while the TV increased (P < 0.01). There was one subject had decreased TV and elevated Rua (P < 0.001).
  
  
  CONCLUSIONS
  Decreased IAP significantly increased caudal TD, and elevated IAP significantly increased cranial TD. However, the mechanism of UA collapsibility appears primarily mediated by changes in lung volume rather than tracheal traction effect. TV plays an independent role in the mechanism of UA collapsibility.
authors.forename: Shu-Lin
authors.initials: SL
authors.lastname: Ren
authors.forename: Yan-Ru
authors.initials: YR
authors.lastname: Li
authors.affiliation: Department of General Surgery, Beijing Tongren Hospital, Capital Medical University, Beijing 100730, China.
authors.forename: Ji-Xiang
authors.initials: JX
authors.lastname: Wu
authors.forename: Jing-Ying
authors.initials: JY
authors.lastname: Ye
authors.forename: Rachel
authors.initials: R
authors.lastname: Jen
mesh_terms: D000403:Airway Resistance / Q000502:physiology; D000818:Animals; D005260:Female; D008176:Lung Volume Measurements; D009767:Obesity, Morbid / Q000503:physiopathology*; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology; D013552:Swine; D013990:Tidal Volume / Q000502:physiology; D014132:Trachea / Q000502:physiology