title: The Diaphragm Acts as a Brake during Expiration to Prevent Lung Collapse.
abstract: The diaphragm is the major inspiratory muscle and is assumed to relax during expiration. However, electrical postinspiratory activity has been observed. Whether there is an expiratory diaphragmatic contraction that preserves lung patency has yet to be explored.
  
  
  
  We hypothesized the occurrence of an expiratory diaphragmatic contraction directed at stabilizing peripheral airways and preventing or reducing cyclic expiratory lung collapse.
  
  
  
  Mild acute respiratory distress syndrome was induced in 10 anesthetized, spontaneously breathing pigs. Lung volume was decreased by lowering end-expiratory airway pressure in a stepwise manner. We recorded the diaphragmatic electric activity during expiration, dynamic computed tomographic scans, and respiratory mechanics. In five pigs, the same protocol was repeated during mechanical ventilation after muscle paralysis.
  
  
  
  Diaphragmatic electric activity during expiration increased by decreasing end-expiratory lung volume during spontaneous breathing. This enhanced the diaphragm muscle force, to a greater extent with lower lung volume, indicating a diaphragmatic electromechanical coupling during spontaneous expiration. In turn, the resulting diaphragmatic contraction delayed and reduced the expiratory collapse and increased lung aeration compared with mechanical ventilation with muscle paralysis and absence of diaphragmatic activity.
  
  
  
  The diaphragm is an important regulator of expiration. Its expiratory activity seems to preserve lung volume and to protect against lung collapse. The loss of diaphragmatic expiratory contraction during mechanical ventilation and muscle paralysis may be a contributing factor to unsuccessful respiratory support.
authors.affiliation: 1 Hedenstierna Laboratory, Department of Surgical Sciences.|2 Department of Emergency and Organ Transplant, University of Bari, Bari, Italy.
authors.forename: Mariangela
authors.identifier: 0000-0001-5668-7399
authors.initials: M
authors.lastname: Pellegrini
authors.affiliation: 3 Hedenstierna Laboratory, Department of Medical Sciences, and.
authors.forename: Göran
authors.initials: G
authors.lastname: Hedenstierna
authors.affiliation: 1 Hedenstierna Laboratory, Department of Surgical Sciences.
authors.forename: Agneta
authors.initials: A
authors.lastname: Roneus
authors.affiliation: 4 Section of Radiology, Department of Surgical Sciences, Uppsala University, Uppsala, Sweden; and.
authors.forename: Monica
authors.initials: M
authors.lastname: Segelsjö
authors.affiliation: 1 Hedenstierna Laboratory, Department of Surgical Sciences.
authors.forename: Anders
authors.initials: A
authors.lastname: Larsson
authors.affiliation: 1 Hedenstierna Laboratory, Department of Surgical Sciences.|2 Department of Emergency and Organ Transplant, University of Bari, Bari, Italy.
authors.forename: Gaetano
authors.identifier: 0000-0001-6834-6399
authors.initials: G
authors.lastname: Perchiazzi
mesh_terms: D000818:Animals; D003964:Diaphragm / Q000502:physiology*; D004195:Disease Models, Animal; D045853:Exhalation / Q000502:physiology*; D008168:Lung / Q000000981:diagnostic imaging / Q000503:physiopathology; D001261:Pulmonary Atelectasis / Q000503:physiopathology / Q000517:prevention & control*; D012121:Respiration, Artificial; D012128:Respiratory Distress Syndrome / Q000000981:diagnostic imaging / Q000503:physiopathology*; D013552:Swine; D014057:Tomography, X-Ray Computed
keywords: assisted mechanical ventilation; computed tomography imaging; lung collapse; mild acute respiratory distress syndrome; spontaneous breathing