Regional uptake of radioactive oxygen, carbon monoxide and carbon dioxide in the lungs of patients with mitral stenosis.

HE inhalation of radioactive oxygen (0 ir ') with external chest counting allows the measurement of regional ventilation and oxygen uptake in the lung. 1 The subject inhales a measured volume of air containing a minute amount of oxygen-15 and holds his breath for 10 to 15 seconds. The initial peak counting rate is determined by the ventilation of the core of lung tissue between the counters, and the subsequent fall of counts during apnea is related to the oxygen uptake. By combining oxygen-15 with carbon to form labeled carbon monoxide, the transfer of which is diffusion limited, measurements of regional diffusing capacity per unit of lung volume can be made. 2 Oxygen-15-labeled carbon dioxide, which diffuses very rapidly, allows measurement of regional blood flow per unit lung volume. 3 The present paper reports the results obtained by applying these technics to patients with mitral stenosis and the conclusions drawn about the regional distribution of pulmonary blood flow in this disease. Methods Oxygen-15 was prepared by deuteron bombardment of nitrogen molecules in the Medical Research Council cyclotron at Hammersmith Hospital. The target gas, 3 per cent of oxygen in nitrogen, was circulated through the bombardment box and passed rapidly to the adjoining laboratory using a continuous flow system. This gas was diluted in a secondary system so that the final radioactivity was about 5 mc./L. of air. The radioactivity was monitored continuously in a re-entrant ionization chamber. For oxygen measurements this gas was used unaltered, but by use of 2 furnaces all the oxygen could be converted to either carbon monoxide or dioxide as desired. Carbon monoxide was made by passing the radioactive gas from the cyclotron over heated charcoal at 900 C. and removing the small proportion of carbon dioxide in a sodalime absorber. Carbon dioxide was made by passing the oxygen-15 over heated charcoal at 450 C, and converting residual monoxide to dioxide by passing the mixture over copper oxide at 900 C. The completeness of chemical conversion was checked frequently using a mass spectrometer to measure oxygen and carbon dioxide and an infra red analyzer to measure carbon monoxide. Oxygen-15 has a half-life of only 2 minutes and the maximum radiation dose to the blood or to any part of the body for 6 breaths of 1 L. each was calculated to be less than 400 millirads. This dose is comparable with that given to the lung …