[Quantitative regional alveolar volume and specific ventilation (V/VA) in healthy subjects measured with positron...

We have measured quantitative regional alveolar volume and specific ventilation in healthy subjects by Nitrogen-13 gas and Positron Emission Tomography. Studies have proceeded in the supine position. Subjects have rebreathed N-13 gas in closed circuit. After radioactivity has reached equilibrium, Scan was carried out. During equilibrium, we have taken radioactive gas from the closed circuit to make quantitative alveolar volume and we have measured the radioactivity by well counter. This value means radioactivity in unit of thoracic volume. Well counts/PET counts denote alveolar volume/thoracic volume. After equilibrium, RI has been washed out by air, during the washout phase we have 3 sequential images. Using these sequential images, we have fitted RI activity in the washout phase monoexponential curve. Index of the monoexponential curve means -V/V, if we do not consider rebreathing from dead space. The data shows a large alveolar volume in the ventral region compared to that in the dorsal region, and also a high V/V in the dorsal region compared to that in the ventral region. It seems that the error of V/V in healthy subjects due to rebreathing from dead space is about 8%.