[Determination of regional ventilation-perfusion ratio with xenon-133].

Knowledge of the regional ventilation/perfusion ratio is of great interest for the diagnosis and therapy of disorders of pulmonary function. By injecting intravenously a bolus of Xe-133 during breathholding and by recording the influx of activity into the lung with a scintillation camera and analogue tape storage, the regional perfusion of the lungs can be determined, using the count-rate increase per unit time. Once the maximum count-rate is reached the patient is allowed to breathe normally. The slope of the count-rate decrease over the lungs is a measure of ventilation. The regional ventilation/perfusion ratio is calculated by dividing these two indices. Regional disturbances of the ratio are the most frequent cause of hypoxia. The demonstration of such disturbances are therefore of significance in the diagnosis and therapeutic control of pulmonary diseases.