title: The Effect of Compartmental Asymmetry on the Monitoring of Pulmonary Mechanics and Lung Volumes.
abstract: BACKGROUND
  Esophageal pressure measurement for computation of transpulmonary pressure (Ptp) has begun to be incorporated into clinical use for evaluating forces across the lungs. Gaps exist in our understanding of how esophageal pressure (and therefore Ptp), a value measured at a single site, responds when respiratory system compartments are asymmetrically affected by whole-lung atelectasis or unilateral injury as well as changes in chest wall compliance. We reasoned that Ptpwould track with aerated volume changes as estimated by functional residual capacity (FRC) and tidal volume. We examined this hypothesis in the setting of asymmetric lungs and changes in intra-abdominal pressure.
  
  
  METHODS
  This study was conducted in the animal laboratory of a university-affiliated hospital. Models of unilateral atelectasis and unilateral and bilateral lung injury exposed to intra-abdominal hypertension (IAH) in 10 deeply sedated mechanically ventilated swine. Atelectasis was created by balloon occlusion of the left main bronchus. Unilateral lung injury was induced by saline lavage of isolated right lung. Diffuse lung injury was induced by saline lavage of both lungs. The peritoneum was insufflated with air to create a model of pressure-regulated IAH. We measured esophageal pressures, airway pressures, FRC by gas dilution, and oxygenation.
  
  
  RESULTS
  FRC was reduced by IAH in normal lungs (P < .001) and both asymmetric lung pathologies (P < .001). Ptpat end-expiration was decreased by IAH in bilateral (P = .001) and unilateral lung injury (P = .003) as well as unilateral atelectasis (P = .019). In the setting of both lung injury models, end-expiratory Ptpshowed a moderate correlation in tracking with FRC.
  
  
  CONCLUSIONS
  Ptptracks with aerated lung volume in the setting of thoracic asymmetry and changes in intra-abdominal pressure. However, used alone, it cannot distinguish the relative contributions of air-space distention and recruitment of lung units.
authors: University of Minnesota, Minneapolis, Minnesota and Regions Hospital, Saint Paul, Minnesota.
authors: Joseph C
authors: JC
authors: Keenan
authors: University of Minnesota, Minneapolis, Minnesota and Regions Hospital, Saint Paul, Minnesota.
authors: Gustavo A
authors: GA
authors: Cortes-Puentes
authors: Hennepin County Medical Center, Minneapolis, Minnesota.
authors: Alexander B
authors: AB
authors: Adams
authors: University of Minnesota, Minneapolis, Minnesota and Regions Hospital, Saint Paul, Minnesota.
authors: David J
authors: DJ
authors: Dries
authors: University of Minnesota, Minneapolis, Minnesota and Regions Hospital, Saint Paul, Minnesota.
authors: John J
authors: JJ
authors: Marini
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D004947:Esophagus / Q000503:physiopathology; D005652:Functional Residual Capacity; D059325:Intra-Abdominal Hypertension / Q000150:complications; D008168:Lung / Q000503:physiopathology; D008170:Lung Compliance; D055370:Lung Injury / Q000209:etiology / Q000503:physiopathology*; D000072277:Maximal Respiratory Pressures / Q000379:methods*; D010101:Oxygen Consumption; D011312:Pressure; D001261:Pulmonary Atelectasis / Q000209:etiology / Q000503:physiopathology*; D012121:Respiration, Artificial / Q000379:methods*; D015656:Respiratory Mechanics / Q000502:physiology*; D013552:Swine
keywords: animal model; esophageal pressure; functional residual capacity; intra-abdominal hypertension; lung injury; mechanical ventilation