title: Spontaneous breathing affects the spatial ventilation and perfusion distribution during mechanical ventilatory support.
abstract: OBJECTIVE
  In acute respiratory failure, gas exchange improves with spontaneous breathing during airway pressure release ventilation (APRV). The mechanisms for this improvement are not fully clear. We have shown that APRV with spontaneous breathing reopens nonaerated lung tissue in dorsal juxtadiaphragmatic regions. We hypothesized that spontaneous breathing during APRV may redistribute ventilation and perfusion toward these reopened regions.
  
  
  METHODS
  Prospective, randomized, controlled study.
  
  
  METHODS
  Animal research laboratory
  
  
  METHODS
  Twenty controlled mechanically ventilated pigs.
  
  
  METHODS
  Lung injury was induced by injection of oleic acid into the central circulation; thereafter, pigs were randomized to APRV with or without spontaneous breathing. To induce spontaneous breathing during APRV with spontaneous breathing, the mechanical respiratory rate was decreased by 50% in this group.
  
  
  RESULTS
  We measured respiratory mechanics, hemodynamics, gas exchange including the multiple inert gas elimination technique, and the spatial ventilation and perfusion distribution using single photon emission tomography. At similar minute ventilation and airway pressures, shunt remained stable during APRV with spontaneous breathing, whereas it increased during APRV without spontaneous breathing during the 2-hr study period (p = .006). Single photon emission tomography showed more ventilation (p < .001) and pulmonary blood (p < .025) flow in dorsal, juxtadiaphragmatic lung regions when spontaneous breathing was present.
  
  
  CONCLUSIONS
  The beneficial effects of spontaneous breathing on intrapulmonary shunt and oxygenation are explained both by increased ventilation of aerated dependent lung tissue and by opening up nonaerated tissue so that ventilation is distributed to a larger share of the lung. Redistribution of perfusion is possibly secondary to the altered ventilation. The overall effect is a more efficient use of available lung tissue for gas exchange.
authors.affiliation: Department of Clinical Physiology, Universities of Göttingen and Bonn, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Neumann
authors.forename: Hermann
authors.initials: H
authors.lastname: Wrigge
authors.forename: Jörg
authors.initials: J
authors.lastname: Zinserling
authors.forename: Jose
authors.initials: J
authors.lastname: Hinz
authors.forename: Enn
authors.initials: E
authors.lastname: Maripuu
authors.forename: Lars G
authors.initials: LG
authors.lastname: Andersson
authors.forename: Christian
authors.initials: C
authors.lastname: Putensen
authors.forename: Göran
authors.initials: G
authors.lastname: Hedenstierna
mesh_terms: D000818:Animals; D001794:Blood Pressure; D045422:Continuous Positive Airway Pressure; D011652:Pulmonary Circulation; D011659:Pulmonary Gas Exchange; D011877:Radionuclide Imaging; D012119:Respiration; D012128:Respiratory Distress Syndrome / Q000000981:diagnostic imaging / Q000503:physiopathology*; D013552:Swine; D014692:Ventilation-Perfusion Ratio