title: Haemodynamic stability and pulmonary shunt during spontaneous breathing and mechanical ventilation in porcine lung collapse.
abstract: BACKGROUND
  We investigated the haemodynamic stability of a novel porcine model of lung collapse induced by negative pressure application (NPA). A secondary aim was to study whether pulmonary shunt correlates with cardiac output (CO).
  
  
  METHODS
  In 12 anaesthetized and relaxed supine piglets, lung collapse was induced by NPA (-50 kPa). Six animals resumed spontaneous breathing (SB) after 15 min; the other six animals were kept on mechanical ventilation (MV) at respiratory rate and tidal volume (V(T) ) that corresponded to SB. All animals were followed for 135 min with blood gas analysis and detailed haemodynamic monitoring.
  
  
  RESULTS
  Haemodynamics and gas exchange were stable in both groups during the experiment with arterial oxygen tension (PaO(2) )/inspired fraction of oxygen (FiO(2) ) and pulmonary artery occlusion pressure being higher, venous admixture (Q(va) /Q(t) ) and pulmonary perfusion pressure being lower in the SB group. CO was similar in both groups, showing slight decrease over time in the SB group. During MV, Q(va) /Q(t)  increased with CO (slope: 4.3 %min/l; P < 0.001), but not so during SB (slope: 0.55 %min/l; P = 0.16).
  
  
  CONCLUSIONS
  This porcine lung collapse model is reasonably stable in terms of haemodynamics for at least 2 h irrespective of the mode of ventilation. SB achieves higher PaO(2) /FiO(2)  and lower Q(va) /Q(t)  compared with MV. During SB, Q(va) /Q(t)  seems to be less, if at all, affected by CO compared with MV.
authors.affiliation: Department of Surgical Sciences, Anaesthesiology and Critical Care Medicine, Uppsala University, Uppsala, Sweden. laszlo.vimlati@surgsci.uu.se
authors.forename: L
authors.initials: L
authors.lastname: Vimláti
authors.forename: A
authors.initials: A
authors.lastname: Larsson
authors.forename: G
authors.initials: G
authors.lastname: Hedenstierna
authors.forename: M
authors.initials: M
authors.lastname: Lichtwarck-Aschoff
mesh_terms: D000465:Algorithms; D000818:Animals; D019540:Area Under Curve; D001794:Blood Pressure / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology; D045422:Continuous Positive Airway Pressure; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology*; D011175:Positive-Pressure Respiration; D001261:Pulmonary Atelectasis / Q000503:physiopathology*; D011659:Pulmonary Gas Exchange; D011669:Pulmonary Wedge Pressure / Q000502:physiology; D012119:Respiration; D012121:Respiration, Artificial; D013318:Stroke Volume / Q000502:physiology; D013552:Swine; D013815:Thermodilution