| Abstract: | We describe a technique to obtain non-invasively regional pulmonary ventilation–perfusion ratios (V˙A/Q˙) using single photon emission computed tomography (SPECT) and continuous infusion of 133Xe. Single photon transmission tomography was used for attenuation correction, for delineation of the lungs and for V˙A/Q˙ calculations. Data are presented for six normal subjects and compared to those for two patients with moderate chronic obstructive pulmonary disease (COPD). The mean V˙A/Q˙ for the whole lung of the normal subjects ranged from 0·49 to 0·65, group mean 0·56 ± 0·07 (1 SD), and there was no significant difference between the right and left lung. The consistently too low V˙A/Q˙ values are related to the inability to measure regional blood volume and the low resolution of the scintillation camera, giving an under-estimation of tracer input. For the normal subjects, the dispersion of V˙A/Q˙, as defined by the standard deviation of the individual distribution functions, ranged from 0·12 to 0·19. One of the patients was characterized by a low mean V˙A/Q˙ of 0·35, and the other patient had a wide dispersion (SD) of V˙A/Q˙ of 0·37. In the normal subjects, a consistent V˙A/Q˙ gradient was found only in the ventrodorsal direction. 133Xe and SPECT can be used to obtain meaningful biological information regarding ventilation/perfusion relationships of potential clinical value. |
