Uneven perfusion and ventilation within lung regions studied with nitrogen-13

Abstract The clearance of nitrogen-13 ( 13 N) from the upper, mid and lower zones was measured with a gamma camera during spontaneous breathing in 10 seated subjects. The clearance was monitored after (a) an intravenous injection of 13 N dissolved in saline and (b) equilibration with 13 N gas in closed circuit. Subjects breathed air first, and then a 30 or 11% oxygen mixture. For any region, the time for 90% elimination (T 90 )_was related to the volume expired by the whole lung during that time ( Ve 90 ). For the mid and lower zones, the clearance was faster ( Ve 90 smaller) after intravenous 13 N than after equilibration with 13 N gas. This difference persisted when 3-% or 11% oxygen was inspired. For the lung overall, the physiological dead space for a mean tidal volume of 884 ml was 277 ml for intravenous 13 N clearance, and 384 ml for 13 N clearance after equilibration. The conclusion drawn for this study are (1) ventilation in relation to volume is uneven within lung regions (2) intraregional perfusion in relation to volume is also uneven (3) at a local level the well-ventilated units are better perfused (4) these inhomogeneities are not affected by raising or lowering the inspired oxygen concentration.