title: Brain versus lung: hierarchy of feedback loops in single-ventricle patients with superior cavopulmonary connection.
abstract: BACKGROUND
  CO2 vasodilates and O2 vasoconstricts the cerebral vascular bed; the opposite is true in the lungs. When the brain and lungs are connected exclusively in series, which feedback loop predominates is unknown. The circulation of the superior cavopulmonary connection (SCPC) provides a unique physiology to answer this question.
  
  
  RESULTS
  To determine cerebral and pulmonary blood flow and to establish the hierarchy of cerebral and pulmonary feedback mechanisms, 12 intubated, ventilated, single-ventricle patients in SCPC physiology (age 2.2+/-0.5 years) underwent magnetic resonance imaging velocity mapping of their jugular veins and aorta in room air, hypercarbia, and 100% O2. Flows in these vessels and arterial blood gases were measured. With 22+/-6 torr CO2 (Pco2) increased from 40 to 63 mm Hg, P<0.01), flow to the brain and lungs increased (1.5 to 2.7 L/min per m2, P=0.0003), Po2 improved (48 to 60 mm Hg, P=0.0004), and cardiac index increased (4.3 to 5.4 L/min per m2, P=0.0003). The increased cardiac index accounted for the increased cerebral and pulmonary blood flow (R=0.73, P=0.02) and cerebral O2 transport increased by 80% (P=0.0005) while preserving body O2 delivery. Hyperoxia did not change cerebral and pulmonary blood flow; Po2 increased 94% (P=0.01).
  
  
  CONCLUSIONS
  The cerebral CO2 feedback loop predominates over the pulmonary one when they directly compete with each other. CO2 has a major impact on flow distribution whereas O2 has little impact. Increased CO2 improves cerebral oxygenation in SCPC patients. This may provide a clue in determining neurological sequelae in SC physiology and may influence timing of Fontan completion.
authors.affiliation: Division of Cardiology, Department of Pediatrics, The Children's Hospital of Philadelphia, The University of Pennsylvania School of Medicine, Philadelphia, Pa 19104, USA. fogel@email.chop.edu
authors.forename: Mark A
authors.initials: MA
authors.lastname: Fogel
authors.forename: Suzanne
authors.initials: S
authors.lastname: Durning
authors.forename: Gil
authors.initials: G
authors.lastname: Wernovsky
authors.forename: Avrum N
authors.initials: AN
authors.lastname: Pollock
authors.forename: J William
authors.initials: JW
authors.lastname: Gaynor
authors.forename: Susan
authors.initials: S
authors.lastname: Nicolson
mesh_terms: D001011:Aorta / Q000503:physiopathology; D002245:Carbon Dioxide / Q000008:administration & dosage / Q000097:blood; D002560:Cerebrovascular Circulation; D002675:Child, Preschool; D025461:Feedback, Physiological / Q000502:physiology*; D005260:Female; D018729:Fontan Procedure; D006352:Heart Ventricles / Q000002:abnormalities* / Q000601:surgery; D018056:Hemorheology; D006801:Humans; D007223:Infant; D007601:Jugular Veins / Q000503:physiopathology; D008279:Magnetic Resonance Imaging; D008297:Male; D009928:Organ Specificity; D010100:Oxygen / Q000008:administration & dosage / Q000097:blood; D011446:Prospective Studies; D011651:Pulmonary Artery / Q000601:surgery; D011652:Pulmonary Circulation; D014661:Vasoconstriction; D014664:Vasodilation; D014682:Vena Cava, Inferior / Q000601:surgery; D014683:Vena Cava, Superior / Q000601:surgery
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen