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Surfactant disaturated-phosphatidylcholine kinetics in acute respiratory distress syndrome by stable isotopes and a two compartment model

Paola E Cogo1* email, Gianna Maria Toffolo2* email, Carlo Ori3* email, Andrea Vianello4* email, Marco Chierici2* email, Antonina Gucciardi1* email, Claudio Cobelli2* email, Aldo Baritussio5* email and Virgilio P Carnielli6,7* email

Department of Pediatrics, University of Padova, Padova, Italy

Department of Information Engineering, University of Padova, Italy

Department of Pharmacology, Anaesthesia and Critical Care, University of Padova, Padova, Italy

Respiratory Unit, General Medical Hospital, Padova, Italy

Department of Medical and Surgical Sciences, University of Padova, Padova, Italy

Neonatal Division, Salesi Children's Hospital, Ancona, Italy

Nutrition Unit, Institute of Child Health and Great Ormond Street Hospital, London, UK

author email corresponding author email* Contributed equally

Respiratory Research 2007, 8:13doi:10.1186/1465-9921-8-13

Published: 21 February 2007

Abstract

Background

In patients with acute respiratory distress syndrome (ARDS), it is well known that only part of the lungs is aerated and surfactant function is impaired, but the extent of lung damage and changes in surfactant turnover remain unclear. The objective of the study was to evaluate surfactant disaturated-phosphatidylcholine turnover in patients with ARDS using stable isotopes.

Methods

We studied 12 patients with ARDS and 7 subjects with normal lungs. After the tracheal instillation of a trace dose of 13C-dipalmitoyl-phosphatidylcholine, we measured the 13C enrichment over time of palmitate residues of disaturated-phosphatidylcholine isolated from tracheal aspirates. Data were interpreted using a model with two compartments, alveoli and lung tissue, and kinetic parameters were derived assuming that, in controls, alveolar macrophages may degrade between 5 and 50% of disaturated-phosphatidylcholine, the rest being lost from tissue. In ARDS we assumed that 5–100% of disaturated-phosphatidylcholine is degraded in the alveolar space, due to release of hydrolytic enzymes. Some of the kinetic parameters were uniquely determined, while others were identified as lower and upper bounds.

Results

In ARDS, the alveolar pool of disaturated-phosphatidylcholine was significantly lower than in controls (0.16 ± 0.04 vs. 1.31 ± 0.40 mg/kg, p < 0.05). Fluxes between tissue and alveoli and de novo synthesis of disaturated-phosphatidylcholine were also significantly lower, while mean resident time in lung tissue was significantly higher in ARDS than in controls. Recycling was 16.2 ± 3.5 in ARDS and 31.9 ± 7.3 in controls (p = 0.08).

Conclusion

In ARDS the alveolar pool of surfactant is reduced and disaturated-phosphatidylcholine turnover is altered.


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