Determination of regional ventilation and perfusion in the lung using xenon and computed tomography

We propose a model to measure both regional ventilation ((V) over dot) and perfusion ((Q) over dot) in which the regional radiodensity (RD) in the lung during xenon (Xe) washin is a function of regional (V) over dot (increasing RD) and (Q) over dot (decreasing RD). We studied five anesthetized, paralyzed, mechanically ventilated, supine sheep. Four 2.5-mm-thick computed tomography (CT) images were simultaneously acquired immediately cephalad to the diaphragm at end inspiration for each breath during 3 min of Xe breathing. Observed changes in RD during Xe washin were used to determine regional (V) over dot and (Q) over dot. For 16 mm(3), displayed more variance than (V) over dot: the coefficient of variance of (Q) over dot (CV(Q) over dot) = 1.58 +/- 0.23, the CV of (V) over dot (CV(V) over dot) = 0.46 +/- 0.07, and the ratio of CV(Q) over dot to CV(V) over dot = 3.5 +/- 1.1. CV(Q) over dot (1.21 +/- 0.37) and the ratio of CV(Q) over dot to CV(V) over dot (2.4 +/- 1.2) were smaller at 1,000-mm(3) scale, but CV(V) over dot (0.53 +/- 0.09) was not, (V) over dot/(Q) over dot distributions also displayed scale dependence: log SD of (V) over dot and log SD of (Q) over dot were 0.79 +/- 0.05 and 0.85 +/- 0.10 for 16-mm(3) and 0.69 +/- 0.20 and 0.67 +/- 0.10 for 1,000-mm(3) regions of lung, respectively. (V) over dot and (Q) over dot measurements made with CT and Xe also demonstrate vertically oriented and isogravitational heterogeneity, which are described using other methodologies. Sequential images acquired by CT during Xe breathing can be used to determine both regional (V) over dot and (Q) over dot noninvasively with high spatial resolution.