title: Right atrial pressure as a measure of ventricular constraint arising from positive end-expiratory pressure during mechanical ventilation of the neonatal lamb.
abstract: OBJECTIVE
  By constraining the heart, the chest wall, lungs, and pericardium limit diastolic filling and thus have a major role in determining cardiac output. Although intermittent positive pressure ventilation and the application of positive end-expiratory pressure amplifies this constraint, no clinical method exists to assess the impact that positive end-expiratory pressure has on ventricular constraint in the newborn. In this study, we tested the hypothesis that a change in right atrial pressure (Pra) reflects the change in ventricular constraint associated with a change in airway pressure.
  
  
  METHODS
  Experimental, comparative animal study.
  
  
  METHODS
  Ritchie Centre for Baby Health Research cardiovascular laboratory. SUBJECTS Neonatal (4-wk-old, n = 6) and newborn (3-day-old, n = 6) Merino/Border-Leicester cross lambs.
  
  
  METHODS
  Lambs were anesthetized (alpha-chloralose and ketamine), ventilated, and instrumented to record Pra, thoracic inferior vena caval pressure (Pivc, saline-filled catheters), and pericardial pressure (Pper, liquid-containing balloon).
  
  
  RESULTS
  Changes (Delta) in Pra, Pivc, and Pper were assessed while airway pressure was rapidly reduced from four set levels of continuous positive airway pressure (2.5, 5, 7.5, and 15 cm H2O) to atmospheric pressure. A strong linear relationship was observed between DeltaPra and DeltaPper (DeltaPra = 0.90 DeltaPper - 0.02, r =.98), and between DeltaPivc and DeltaPper (DeltaPivc = 0.86 DeltaPper - 0.02, r =.98) in both the 4-wk-old lambs and the 3-day-old lambs.
  
  
  CONCLUSIONS
  Our experiments demonstrate that, in the newborn and neonatal lamb, DeltaPra provides an accurate measure of the change in ventricular constraint that accompanies a change in airway pressure, and thus may provide a means of quantifying the magnitude of ventricular constraint imposed by positive end-expiratory pressure and mechanical ventilation during neonatal intensive care.
authors.affiliation: Clinic of Neonatology, Department of Gynecology and Obstetrics, University Hospital, Zurich, Switzerland.
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Fauchère
authors.forename: Adrian M
authors.initials: AM
authors.lastname: Walker
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Grant
mesh_terms: D000367:Age Factors; D000403:Airway Resistance; D000818:Animals; D000831:Animals, Newborn; D001274:Atmospheric Pressure; D016280:Atrial Function, Right; D001795:Blood Pressure Determination / Q000379:methods* / Q000592:standards; D002302:Cardiac Output; D003971:Diastole; D004195:Disease Models, Animal; D006801:Humans; D007231:Infant, Newborn; D016014:Linear Models; D008991:Monitoring, Physiologic / Q000379:methods* / Q000592:standards; D010496:Pericardium / Q000503:physiopathology; D011175:Positive-Pressure Respiration / Q000009:adverse effects* / Q000379:methods*; D012127:Respiratory Distress Syndrome, Newborn / Q000503:physiopathology* / Q000628:therapy*; D012756:Sheep; D014682:Vena Cava, Inferior / Q000503:physiopathology; D016276:Ventricular Function; D017725:Ventricular Pressure