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 lun g during xenon (Xe) washin is a function of regional (V) over dot (increasi ng RD) and (Q) over dot (decreasing RD). We studied five anesthetized, para lyzed, mechanically ventilated, supine sheep. Four 2.5-mm-thick computed to mography (CT) images were simultaneously acquired immediately cephalad to t he diaphragm at end inspiration for each breath during 3 min of Xe breathin g. 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, an d the ratio of CV(Q) over dot to CV(V) over dot = 3.5 +/- 1.1. CV(Q) over d ot (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 +/- 0.0 9) was not, (V) over dot/(Q) over dot distributions also displayed scale de pendence: 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 me asurements made with CT and Xe also demonstrate vertically oriented and iso gravitational heterogeneity, which are described using other methodologies. Sequential images acquired by CT during Xe breathing can be used to determ ine both regional (V) over dot and (Q) over dot noninvasively with high spa tial resolution.