Changes in lung composition and regional perfusion and tissue distribution in patients with ARDS

Abstract

Background & objective ARDS is characterised by bilateral pulmonary infiltrates and refractory hypoxemia attributed to V/Q mismatch. We used dynamic CT to characterise changes in lung composition, regional perfusion and tissue distribution in patients with ARDS in comparison to 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 to 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 (ie 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.

Gas exchange and ventilation–perfusion relationships in the lung

“…Examples of clinical conditions with hypoxaemia due to large intrapulmonary shunts are extensive atelectasis, severe pneumonia and ARDS. In these conditions, the shunt might exceed 50% of total lung blood flow [13,[16][17][18][19]]. …”

“…Several studies have shown that arterial hypoxaemia in these patients is mostly caused by shunt blood flow that might exceed 50% of cardiac output [13,[16][17][18][19]. Low V9A/Q9 regions are either absent or a lesser cause of low PaO 2 [16,17].…”

Imaging in acute lung injury and acute respiratory distress syndrome

“…First, Dakin et al [17] performed a sequence of 15 cardiac-gated single-slice CT scans while infusing intravenous contrast in 11 ALI/ARDS patients. First, Dakin et al [17] performed a sequence of 15 cardiac-gated single-slice CT scans while infusing intravenous contrast in 11 ALI/ARDS patients.…”

Noninvasive Quantitative Assessment of Pulmonary Blood Flow with 18F-FDG PET

“…Key Words: acute lung injury; PET; 18 Assessment of lung perfusion is critical for evaluating the pathophysiology of gas exchange abnormalities and can be performed noninvasively with several imaging tools: SPECT (1), PET (2-4), 4-dimensional CT (5,6), and MR imaging (7,8). PET is particularly attractive because of its high sensitivity and ability to track many other lung pathophysiologic processes (in addition to perfusion), such as ventilation (9,10), ventilation-to-perfusion ratio (11,12), and inflammation (13,14).…”