Comparison of ventilation/perfusion lung-imaging and dead-space measurements in airway disease.

1. Nineteen patients (three normal subjects, at 16 patients with chronic airway disease) were investigated with radionuclide lung-imaging and pulmonary function tests. 2. There was a statistically significant correlation between the ratio of residual volume to total lung capacity and alveolar dead-space ventilation for nitrogen as a percentage of alveolar ventilation (an index of gas mixing inefficiency); rs = 0.54, P less than 0.05. 3. There were statistically significant associations between an abnormal ventilation or perfusion radionuclide lung image and (a) the ratio of residual volume to total lung capacity and (b) the alveolar dead-space ventilation for nitrogen as a percentage of alveolar ventilation. 4. The radionuclide counts from the posterior images were normalized for lung size and injected dose; perfusion counts were then subtracted from ventilation counts at locations from the top to the bottom of the lungs. 5. There was a statistically significant association between low ventilation minus perfusion areas and arterial hypoxia. 6. There was a statistically significant association between high ventilation minus perfusion areas and an increased alveolar dead-space ventilation for carbon dioxide as a percentage of alveolar ventilation.