Regional lung spirometry

Abstract

Forty consenting patients took part in a study to determine lobar, segmental and regional lung volumes and flows as reflected by changes in lung radioactivity measured by nuclear medicine techniques. Two hundred MBq of the gaseous radioisotope 133 Xe were injected into a re-breathing circuit spirometer with an 8 litre capacity and an equilibrium activity of 25 MBq/litre. A posterior dynamic acquisition of 400 frames at 0.125 seconds per frame for the determination of lung volumes and flows was completed, followed by a gas washout period. The acquisition recorded both tidal breathing and 3-6 cycles of maximal inhalation and exhalation after homogenous mixing of the radioactive Xenon inside the lungs and the spirometer, but before significant diffusion of the tracer into the blood. The conversion from millilitres to counts was accomplished by matching a representative breath cycle on the spirometric graph with the same cycle on the radioactivity curve generated on the processed scintigram of the whole lung. A change in volume was hence matched to a change in radioactivity, and a specific radioactivity per millilitre of lung volume was calculated. A region of interest was drawn on the scintigram over a lung lobe or segment. The regional radioactivity change represented a regional breath cycle in this area, with regional volume and flow changes. Spirometric parameters such as lobar vital capacity, tidal volume, residual volume and forced expiratory volume after 1 second were derived by using the previously calculated radioactivity per millilitre of lung volume. Total lung volumes and flows derived from radioactivity changes were compared to the concurrent volumes and flows measured on the attached spirometer, and a close correlation was found.