Abstract
BACKGROUND AND OBJECTIVE: ARDS is characterized by bilateral pulmonary infiltrates and refractory hypoxemia attributed to V/Q mismatch. We used dynamic CT to characterize changes in lung composition, regional perfusion and tissue distribution in patients with ARDS in comparison with healthy subjects. METHODS: The Fick principle was applied to serial attenuation measurements constructed from sequential CT images acquired during the passage of a bolus of iodinated contrast medium in healthy subjects (n=3) and patients with ARDS (n=11). Perfusion was calculated by the Mullani-Gould method and mapped throughout both lungs. Gradients of perfusion and tissue density against vertical height were constructed. RESULTS: In comparison with normal individuals, the tissue component of lungs from patients with ARDS was significantly increased (P<0.05). Blood fraction was unchanged. There was a discernable gradient in tissue density from non dependent to dependent regions in the patients with ARDS that was significantly different from controls. The proportion of perfusion applied to consolidated areas (i.e. shunt) correlated significantly (P<0.05) with the severity of hypoxaemia. CONCLUSIONS: In patients with ARDS there are changes in both lung composition and the distribution of tissue and perfusion that may account in part for the physiological changes that define the syndrome.