Pulmonary perfusion quantified by electron-beam computed tomography: effects of hypoxia and inhaled NO

Patients with acute lung injury may benefit from the manipulation of pulmonary blood flow using inhaled nitric oxide (iNO) to optimise ventilation/perfusion matching. Current techniques for studying changes in regional pulmonary perfusion are difficult to apply clinically. This study therefore investigated the potential of electron-beam computed tomography (EBCT) to quantify the effects of hypoxia and iNO on regional pulmonary perfusion in five healthy subjects. Contrast-enhanced sections were obtained sequentially under conditions of normoxia, hypoxia (fractional concentration of oxygen in inspired gas (FI,O2) 0.12) and hypoxia, with iNO (14.8 parts per million (ppm)) administered during inspiration in the supine position. Regions of interest were placed along the nondependent to dependent axis and values for relative perfusion derived. Under normoxic conditions a vertical gradient of perfusion existed, which became less apparent due to increased perfusion in nondependent regions after the induction of hypoxia (FI,O2 0.12). The addition of iNO (FI,O2 0.12 and NO 14.8 ppm) increased perfusion in all regions of the lung section, suggesting redistribution of pulmonary perfusion from other regions of the lung. Absolute values of perfusion were comparable to those documented with existing techniques. The use of a high spatial-resolution technique confirmed the presence of marked perfusion heterogeneity between anatomically close regions of lung.