British Journal of Anaesthesia, 2001, Vol. 87, No. 3 459-468
© 2001 The Board of Management and Trustees of the British Journal of Anaesthesia
Laboratory Investigations |
Temporal dynamics of lung aeration determined by dynamic CT in a porcine model of ARDS
Departments of 1Anaesthesiology and 2Radiology, Johannes Gutenberg-University Mainz, Langenbeckstr. 1, D-55131 Mainz, Germany*Corresponding author: Department of Anaesthesiology, Johannes Gutenberg-University, Mainz, Langenbeckstr. 1, D-55131 Mainz, Germany
We used dynamic CT to identify two different time constants of lung aeration and their individual contribution to the total increase in cross-sectional lung area in healthy and experimentally damaged lungs. In five healthy pigs, inflation and deflation between 0 and 50 cm H2O was imposed during dynamic (250 ms/image) CT acquisition, and repeated after experimental lung injury by saline lavage. The fractional areas of density ranges, which represent aerated lung parenchyma, were determined planimetrically, and their time for expansion during the manoeuvre was fitted using a bi-exponential model. Thus, two compartments, their sizes, i.e. their relative contributions to lung area aerated by the manoeuvre, and their specific time constants (
) were sought. Healthy lungs were characterized best by a one-compartmental behaviour with one only, both during inflation (median =0.5 s; range 0.4–0.6 s) and deflation (1.2 s; 1.1–1.3 s). In damaged lungs two compartments were found both during inspiration and expiration, with 86% (78–87%) of the recruitable lung area following a short of 0.5 s (0.5–0.6), and 14% (13–22%) following a longer of 9.1 s (8–16.8 s) during inflation. During expiration, damaged lungs had a short of 0.8 s (0.5–1.0 s) for 94% (84–100%) of deflated lung area, and a longer of 26.5 s (7.1–34.3 s) for 6% (0–16%). We conclude that dynamic CT indicates the relative size and temporal behaviour of functional compartments in normal and abnormal lungs. Our findings suggest that after lung damage, cyclic ventilation with inspiratory periods of <10 s duration will not achieve maximum recruitment for a chosen inspiratory pressure. In ARDS, the short expiratory predisposes to atelectasis formation if expiratory times are >1 s.
Br J Anaesth 2001; 87: 459–68
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