Evaluation of alveolar dead space in pulmonary embolism by using functional images

Ventilation studies with Xe-133 gas and Kr-81m gas, and perfusion imagings with Tc-99m MAA were performed in 32 patients for diagnosing pulmonary embolism. Alveolar dead space on functional image was studied. V dot/Q dot ratios were greately increased in the embolic regions within lungs, in which ventilation persisted despite no or decreased blood flow. Therefore, functional image of V dot/Q dot ratios could determine areas of wasted ventilation optically. We could also make laminal display of V dot/Q dot image by reconstruction of singl photon emission CT with continuous inhalation of Kr-81m gas and intravenous injection of Tc-99m albumin microsphere. Few cases showed reduction of %FEV1.0 and many cases were hypoxic hypocapnia. The size and number of alveolar dead space on functional image were not always related to the results of arterial blood gas analysis. It is considered that these findings resulted from the presence of intrapulmonary shunts in the embolic regions. (author)