Unilateral lung function. Comparison of the lateral position test with radionuclide ventilation-perfusion studies

Twenty-seven patients underwent studies of unilateral lung function by the lateral-position test (LPT) and by computer-analyzed radionuclide imaging of ventilation and perfusion. The patients were divided into two groups, symmetric or asymmetric, on the basis of the physical examination of the chest and the chest radiograph. In patients with symmetry, the estimate of unilateral lung function by the LPT and isotopic estimates for unilateral lung volume, unilateral distribution of tidal volume, and unilateral perfusion, agreed within 2 percent, 4 percent, and 3 percent, respectively. In patients with asymmetry, the differences were 9 percent, 8 percent, and 13 percent. In settings of marked unilateral ventilation-perfusion imbalance, the LPT primarily reflected ventilation. Prediction of unilateral ventilatory function based upon the LPT and spirometric measurements agreed closely with unilateral ventilation determined isotopically by 133xenon, even in the presence of chronic obstructive lung disease. Our results confirm that the LPT provides valid information about unilateral lung function.