title: New insights into the aspects of pulmonary diffusing capacity in Fontan patients.
abstract: BACKGROUND
  Patients with a functionally univentricular heart, palliated a.m. Fontan, consequently have non-pulsatile pulmonary blood flow and are known to have a reduced pulmonary diffusing capacity. However, the cause of this reduction remains unclear. We aimed to assess the possible determinants in the aetiology of a reduced diffusing capacity and also to assess whether it could be increased. Furthermore, we aimed to search for predictors of a reduced diffusing capacity.
  
  
  METHODS
  A total of 87 Fontan patients (mean age 16.3 ± 7.6 years) performed advanced pulmonary function tests and maximal cycle ergometer tests. A total of 10 Fontan patients and nine matched controls performed a supine pulmonary function test after a supine rest.
  
  
  RESULTS
  In the sitting pulmonary function test, the mean z-scores were: diffusing capacity, 2.38 ± 1.20; pulmonary capillary blood volume, 2.04 ± 0.80; and alveolar capillary membrane diffusing capacity, 0.14 ± 0.84. In the supine compared with the sitting pulmonary function test, the diffusing capacity increased by 51.7 ± 11.9% in the Fontan group and by 23.3 ± 17.7% in the control group (p < 0.001); moreover, the pulmonary capillary blood volume increased by 48.3 ± 17.4% in the Fontan group and by 20.2 ± 13.9% in the control group (p = 0.001). In a multiple linear regression analysis including the explanatory variables of surgical data and exercise data at rest and peak exercise, the resting cardiac index was an independent predictor of the diffusing capacity (regression coefficient: 0.18, p < 0.001).
  
  
  CONCLUSIONS
  The pulmonary diffusing capacity was reduced in Fontan patients because of a reduced pulmonary capillary blood volume, whereas the alveolar capillary membrane diffusing capacity was preserved. The diffusing capacity was highly increasable in Fontan patients compared with controls, and the resting cardiac index was an independent predictor of the diffusing capacity.
authors.affiliation: 1 Department of Cardiology, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Lars
authors.initials: L
authors.lastname: Idorn
authors.affiliation: 2 Department of Paediatrics and Adolescent Medicine, Section of Paediatric Pulmonary Service, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Birgitte
authors.initials: B
authors.lastname: Hanel
authors.affiliation: 1 Department of Cardiology, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Annette S
authors.initials: AS
authors.lastname: Jensen
authors.affiliation: 3 Department of Paediatrics and Adolescent Medicine, Section of Pediatric Cardiology, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Klaus
authors.initials: K
authors.lastname: Juul
authors.affiliation: 3 Department of Paediatrics and Adolescent Medicine, Section of Pediatric Cardiology, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Jesper I
authors.initials: JI
authors.lastname: Reimers
authors.affiliation: 2 Department of Paediatrics and Adolescent Medicine, Section of Paediatric Pulmonary Service, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Kim G
authors.initials: KG
authors.lastname: Nielsen
authors.affiliation: 1 Department of Cardiology, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Lars
authors.initials: L
authors.lastname: Søndergaard
mesh_terms: D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D002648:Child; D005080:Exercise Test; D005260:Female; D018729:Fontan Procedure; D006330:Heart Defects, Congenital / Q000503:physiopathology / Q000601:surgery*; D006801:Humans; D016014:Linear Models; D008297:Male; D011187:Posture / Q000502:physiology; D011653:Pulmonary Diffusing Capacity / Q000502:physiology*; D012129:Respiratory Function Tests; D016683:Supine Position / Q000502:physiology; D055815:Young Adult